diff --git a/internal/lsp/cache/check.go b/internal/lsp/cache/check.go
index 1b79ddf..5940651 100644
--- a/internal/lsp/cache/check.go
+++ b/internal/lsp/cache/check.go
@@ -21,6 +21,7 @@
 	"golang.org/x/tools/go/ast/astutil"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/event"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
@@ -485,18 +486,16 @@
 			continue
 		}
 		direct := !strings.Contains(diag.Message, "error while importing")
-		args, err := source.MarshalArgs(pkg.compiledGoFiles[0].URI, direct, matches[1])
+		title := fmt.Sprintf("go get package %v", matches[1])
+		cmd, err := command.NewGoGetPackageCommand(title, command.GoGetPackageArgs{
+			URI:        protocol.URIFromSpanURI(pkg.compiledGoFiles[0].URI),
+			AddRequire: direct,
+			Pkg:        matches[1],
+		})
 		if err != nil {
 			return err
 		}
-		diag.SuggestedFixes = append(diag.SuggestedFixes, source.SuggestedFix{
-			Title: fmt.Sprintf("go get package %v", matches[1]),
-			Command: &protocol.Command{
-				Title:     fmt.Sprintf("go get package %v", matches[1]),
-				Command:   source.CommandGoGetPackage.ID(),
-				Arguments: args,
-			},
-		})
+		diag.SuggestedFixes = append(diag.SuggestedFixes, source.SuggestedFixFromCommand(cmd))
 	}
 	return nil
 }
diff --git a/internal/lsp/cache/mod.go b/internal/lsp/cache/mod.go
index d47efe3..99f9a22 100644
--- a/internal/lsp/cache/mod.go
+++ b/internal/lsp/cache/mod.go
@@ -15,6 +15,7 @@
 	"golang.org/x/mod/module"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/gocommand"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
@@ -285,7 +286,12 @@
 	disabledByGOPROXY := strings.Contains(goCmdError, "disabled by GOPROXY=off")
 	shouldAddDep := strings.Contains(goCmdError, "to add it")
 	if innermost != nil && (disabledByGOPROXY || shouldAddDep) {
-		args, err := source.MarshalArgs(fh.URI(), false, []string{fmt.Sprintf("%v@%v", innermost.Path, innermost.Version)})
+		title := fmt.Sprintf("Download %v@%v", innermost.Path, innermost.Version)
+		cmd, err := command.NewAddDependencyCommand(title, command.DependencyArgs{
+			URI:        protocol.URIFromSpanURI(fh.URI()),
+			AddRequire: false,
+			GoCmdArgs:  []string{fmt.Sprintf("%v@%v", innermost.Path, innermost.Version)},
+		})
 		if err != nil {
 			return nil
 		}
@@ -294,19 +300,12 @@
 			msg = fmt.Sprintf("%v@%v has not been downloaded", innermost.Path, innermost.Version)
 		}
 		return &source.Diagnostic{
-			URI:      fh.URI(),
-			Range:    rng,
-			Severity: protocol.SeverityError,
-			Message:  msg,
-			Source:   source.ListError,
-			SuggestedFixes: []source.SuggestedFix{{
-				Title: fmt.Sprintf("Download %v@%v", innermost.Path, innermost.Version),
-				Command: &protocol.Command{
-					Title:     source.CommandAddDependency.Title,
-					Command:   source.CommandAddDependency.ID(),
-					Arguments: args,
-				},
-			}},
+			URI:            fh.URI(),
+			Range:          rng,
+			Severity:       protocol.SeverityError,
+			Message:        msg,
+			Source:         source.ListError,
+			SuggestedFixes: []source.SuggestedFix{source.SuggestedFixFromCommand(cmd)},
 		}
 	}
 	diagSource := source.ListError
diff --git a/internal/lsp/cache/mod_tidy.go b/internal/lsp/cache/mod_tidy.go
index 59f131c..e8a8547 100644
--- a/internal/lsp/cache/mod_tidy.go
+++ b/internal/lsp/cache/mod_tidy.go
@@ -18,6 +18,7 @@
 	"golang.org/x/mod/modfile"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/gocommand"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/diff"
 	"golang.org/x/tools/internal/lsp/protocol"
@@ -172,13 +173,15 @@
 	if err != nil {
 		return nil
 	}
-	args, err := source.MarshalArgs(protocol.URIFromSpanURI(fh.URI()))
-	if err != nil {
-		return nil
-	}
-
+	// TODO(rFindley): we shouldn't really need to call three constructors here.
+	//                 Reconsider this.
+	args := command.URIArg{protocol.URIFromSpanURI(fh.URI())}
 	switch {
 	case isInconsistentVendor:
+		cmd, err := command.NewVendorCommand("Run go mod vendor", args)
+		if err != nil {
+			return nil
+		}
 		return &source.Diagnostic{
 			URI:      fh.URI(),
 			Range:    rng,
@@ -186,17 +189,18 @@
 			Source:   source.ListError,
 			Message: `Inconsistent vendoring detected. Please re-run "go mod vendor".
 See https://github.com/golang/go/issues/39164 for more detail on this issue.`,
-			SuggestedFixes: []source.SuggestedFix{{
-				Title: source.CommandVendor.Title,
-				Command: &protocol.Command{
-					Command:   source.CommandVendor.ID(),
-					Title:     source.CommandVendor.Title,
-					Arguments: args,
-				},
-			}},
+			SuggestedFixes: []source.SuggestedFix{source.SuggestedFixFromCommand(cmd)},
 		}
 
 	case isGoSumUpdates:
+		tidyCmd, err := command.NewTidyCommand("Run go mod tidy", args)
+		if err != nil {
+			return nil
+		}
+		updateCmd, err := command.NewUpdateGoSumCommand("Update go.sum", args)
+		if err != nil {
+			return nil
+		}
 		return &source.Diagnostic{
 			URI:      fh.URI(),
 			Range:    rng,
@@ -204,22 +208,8 @@
 			Source:   source.ListError,
 			Message:  `go.sum is out of sync with go.mod. Please update it or run "go mod tidy".`,
 			SuggestedFixes: []source.SuggestedFix{
-				{
-					Title: source.CommandTidy.Title,
-					Command: &protocol.Command{
-						Command:   source.CommandTidy.ID(),
-						Title:     source.CommandTidy.Title,
-						Arguments: args,
-					},
-				},
-				{
-					Title: source.CommandUpdateGoSum.Title,
-					Command: &protocol.Command{
-						Command:   source.CommandUpdateGoSum.ID(),
-						Title:     source.CommandUpdateGoSum.Title,
-						Arguments: args,
-					},
-				},
+				source.SuggestedFixFromCommand(tidyCmd),
+				source.SuggestedFixFromCommand(updateCmd),
 			},
 		}
 	}
@@ -385,24 +375,22 @@
 	if err != nil {
 		return nil, err
 	}
-	args, err := source.MarshalArgs(m.URI, onlyDiagnostic, req.Mod.Path)
+	title := fmt.Sprintf("Remove dependency: %s", req.Mod.Path)
+	cmd, err := command.NewRemoveDependencyCommand(title, command.RemoveDependencyArgs{
+		URI:            protocol.URIFromSpanURI(m.URI),
+		OnlyDiagnostic: onlyDiagnostic,
+		ModulePath:     req.Mod.Path,
+	})
 	if err != nil {
 		return nil, err
 	}
 	return &source.Diagnostic{
-		URI:      m.URI,
-		Range:    rng,
-		Severity: protocol.SeverityWarning,
-		Source:   source.ModTidyError,
-		Message:  fmt.Sprintf("%s is not used in this module", req.Mod.Path),
-		SuggestedFixes: []source.SuggestedFix{{
-			Title: fmt.Sprintf("Remove dependency: %s", req.Mod.Path),
-			Command: &protocol.Command{
-				Title:     source.CommandRemoveDependency.Title,
-				Command:   source.CommandRemoveDependency.ID(),
-				Arguments: args,
-			},
-		}},
+		URI:            m.URI,
+		Range:          rng,
+		Severity:       protocol.SeverityWarning,
+		Source:         source.ModTidyError,
+		Message:        fmt.Sprintf("%s is not used in this module", req.Mod.Path),
+		SuggestedFixes: []source.SuggestedFix{source.SuggestedFixFromCommand(cmd)},
 	}, nil
 }
 
@@ -459,24 +447,22 @@
 			return nil, err
 		}
 	}
-	args, err := source.MarshalArgs(pm.Mapper.URI, !req.Indirect, []string{req.Mod.Path + "@" + req.Mod.Version})
+	title := fmt.Sprintf("Add %s to your go.mod file", req.Mod.Path)
+	cmd, err := command.NewAddDependencyCommand(title, command.DependencyArgs{
+		URI:        protocol.URIFromSpanURI(pm.Mapper.URI),
+		AddRequire: !req.Indirect,
+		GoCmdArgs:  []string{req.Mod.Path + "@" + req.Mod.Version},
+	})
 	if err != nil {
 		return nil, err
 	}
 	return &source.Diagnostic{
-		URI:      pm.Mapper.URI,
-		Range:    rng,
-		Severity: protocol.SeverityError,
-		Source:   source.ModTidyError,
-		Message:  fmt.Sprintf("%s is not in your go.mod file", req.Mod.Path),
-		SuggestedFixes: []source.SuggestedFix{{
-			Title: fmt.Sprintf("Add %s to your go.mod file", req.Mod.Path),
-			Command: &protocol.Command{
-				Title:     source.CommandAddDependency.Title,
-				Command:   source.CommandAddDependency.ID(),
-				Arguments: args,
-			},
-		}},
+		URI:            pm.Mapper.URI,
+		Range:          rng,
+		Severity:       protocol.SeverityError,
+		Source:         source.ModTidyError,
+		Message:        fmt.Sprintf("%s is not in your go.mod file", req.Mod.Path),
+		SuggestedFixes: []source.SuggestedFix{source.SuggestedFixFromCommand(cmd)},
 	}, nil
 }
 
diff --git a/internal/lsp/cmd/workspace.go b/internal/lsp/cmd/workspace.go
index 88531a7..a099599 100644
--- a/internal/lsp/cmd/workspace.go
+++ b/internal/lsp/cmd/workspace.go
@@ -9,6 +9,7 @@
 	"flag"
 	"fmt"
 
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/tool"
@@ -82,7 +83,11 @@
 		return err
 	}
 	defer conn.terminate(ctx)
-	params := &protocol.ExecuteCommandParams{Command: source.CommandGenerateGoplsMod.ID()}
+	cmd, err := command.NewGenerateGoplsModCommand("", command.URIArg{})
+	if err != nil {
+		return err
+	}
+	params := &protocol.ExecuteCommandParams{Command: cmd.Command, Arguments: cmd.Arguments}
 	if _, err := conn.ExecuteCommand(ctx, params); err != nil {
 		return fmt.Errorf("executing server command: %v", err)
 	}
diff --git a/internal/lsp/code_action.go b/internal/lsp/code_action.go
index b796433..1ab91fb 100644
--- a/internal/lsp/code_action.go
+++ b/internal/lsp/code_action.go
@@ -13,6 +13,7 @@
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/imports"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/mod"
 	"golang.org/x/tools/internal/lsp/protocol"
@@ -264,7 +265,7 @@
 		}
 		// If the suggested fix for the diagnostic is expected to be separate,
 		// see if there are any supported commands available.
-		if analyzer.Command != nil {
+		if analyzer.Fix != "" {
 			action, err := diagnosticToCommandCodeAction(ctx, snapshot, srcErr, &diag, protocol.QuickFix)
 			if err != nil {
 				return nil, nil, err
@@ -362,7 +363,7 @@
 		if !a.IsEnabled(snapshot.View()) {
 			continue
 		}
-		if a.Command == nil {
+		if a.Fix == "" {
 			event.Error(ctx, "convenienceFixes", fmt.Errorf("no suggested fixes for convenience analyzer %s", a.Analyzer.Name))
 			continue
 		}
@@ -399,10 +400,14 @@
 	if analyzer == nil {
 		return nil, fmt.Errorf("no convenience analyzer for source %s", sd.Source)
 	}
-	if analyzer.Command == nil {
-		return nil, fmt.Errorf("no command for convenience analyzer %s", analyzer.Analyzer.Name)
+	if analyzer.Fix == "" {
+		return nil, fmt.Errorf("no fix for convenience analyzer %s", analyzer.Analyzer.Name)
 	}
-	jsonArgs, err := source.MarshalArgs(sd.URI, sd.Range)
+	cmd, err := command.NewApplyFixCommand(sd.Message, command.ApplyFixArgs{
+		URI:   protocol.URIFromSpanURI(sd.URI),
+		Range: sd.Range,
+		Fix:   analyzer.Fix,
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -414,11 +419,7 @@
 		Title:       sd.Message,
 		Kind:        kind,
 		Diagnostics: diagnostics,
-		Command: &protocol.Command{
-			Command:   analyzer.Command.ID(),
-			Title:     sd.Message,
-			Arguments: jsonArgs,
-		},
+		Command:     &cmd,
 	}, nil
 }
 
@@ -430,10 +431,6 @@
 	if err != nil {
 		return nil, err
 	}
-	jsonArgs, err := source.MarshalArgs(uri, rng)
-	if err != nil {
-		return nil, err
-	}
 	_, pgf, err := source.GetParsedFile(ctx, snapshot, fh, source.NarrowestPackage)
 	if err != nil {
 		return nil, errors.Errorf("getting file for Identifier: %w", err)
@@ -442,22 +439,36 @@
 	if err != nil {
 		return nil, err
 	}
-	var commands []*source.Command
+	puri := protocol.URIFromSpanURI(uri)
+	var commands []protocol.Command
 	if _, ok, _ := source.CanExtractFunction(snapshot.FileSet(), srng, pgf.Src, pgf.File); ok {
-		commands = append(commands, source.CommandExtractFunction)
+		cmd, err := command.NewApplyFixCommand("Extract to function", command.ApplyFixArgs{
+			URI:   puri,
+			Fix:   source.ExtractFunction,
+			Range: rng,
+		})
+		if err != nil {
+			return nil, err
+		}
+		commands = append(commands, cmd)
 	}
 	if _, _, ok, _ := source.CanExtractVariable(srng, pgf.File); ok {
-		commands = append(commands, source.CommandExtractVariable)
+		cmd, err := command.NewApplyFixCommand("Extract variable", command.ApplyFixArgs{
+			URI:   puri,
+			Fix:   source.ExtractVariable,
+			Range: rng,
+		})
+		if err != nil {
+			return nil, err
+		}
+		commands = append(commands, cmd)
 	}
 	var actions []protocol.CodeAction
-	for _, command := range commands {
+	for _, cmd := range commands {
 		actions = append(actions, protocol.CodeAction{
-			Title: command.Title,
-			Kind:  protocol.RefactorExtract,
-			Command: &protocol.Command{
-				Command:   command.ID(),
-				Arguments: jsonArgs,
-			},
+			Title:   cmd.Title,
+			Kind:    protocol.RefactorExtract,
+			Command: &cmd,
 		})
 	}
 	return actions, nil
@@ -574,17 +585,13 @@
 		return nil, nil
 	}
 
-	jsonArgs, err := source.MarshalArgs(uri, tests, benchmarks)
+	cmd, err := command.NewTestCommand("Run tests and benchmarks", protocol.URIFromSpanURI(uri), tests, benchmarks)
 	if err != nil {
 		return nil, err
 	}
 	return []protocol.CodeAction{{
-		Title: source.CommandTest.Name,
-		Kind:  protocol.GoTest,
-		Command: &protocol.Command{
-			Title:     source.CommandTest.Title,
-			Command:   source.CommandTest.ID(),
-			Arguments: jsonArgs,
-		},
+		Title:   cmd.Title,
+		Kind:    protocol.GoTest,
+		Command: &cmd,
 	}}, nil
 }
diff --git a/internal/lsp/code_lens.go b/internal/lsp/code_lens.go
index b1c6ba5..6e371fc 100644
--- a/internal/lsp/code_lens.go
+++ b/internal/lsp/code_lens.go
@@ -10,6 +10,7 @@
 	"sort"
 
 	"golang.org/x/tools/internal/event"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/mod"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
@@ -21,26 +22,26 @@
 	if !ok {
 		return nil, err
 	}
-	var lensFuncs map[string]source.LensFunc
+	var lenses map[command.Command]source.LensFunc
 	switch fh.Kind() {
 	case source.Mod:
-		lensFuncs = mod.LensFuncs()
+		lenses = mod.LensFuncs()
 	case source.Go:
-		lensFuncs = source.LensFuncs()
+		lenses = source.LensFuncs()
 	default:
 		// Unsupported file kind for a code lens.
 		return nil, nil
 	}
 	var result []protocol.CodeLens
-	for lens, lf := range lensFuncs {
-		if !snapshot.View().Options().Codelenses[lens] {
+	for cmd, lf := range lenses {
+		if !snapshot.View().Options().Codelenses[string(cmd)] {
 			continue
 		}
 		added, err := lf(ctx, snapshot, fh)
 		// Code lens is called on every keystroke, so we should just operate in
 		// a best-effort mode, ignoring errors.
 		if err != nil {
-			event.Error(ctx, fmt.Sprintf("code lens %s failed", lens), err)
+			event.Error(ctx, fmt.Sprintf("code lens %s failed", cmd), err)
 			continue
 		}
 		result = append(result, added...)
diff --git a/internal/lsp/command.go b/internal/lsp/command.go
index 8b1b8e0..a11b8b3 100644
--- a/internal/lsp/command.go
+++ b/internal/lsp/command.go
@@ -18,6 +18,7 @@
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/gocommand"
 	"golang.org/x/tools/internal/lsp/cache"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
@@ -37,12 +38,12 @@
 		return nil, fmt.Errorf("%s is not a supported command", params.Command)
 	}
 
-	cmd := &commandHandler{
+	handler := &commandHandler{
 		ctx:    ctx,
 		s:      s,
 		params: params,
 	}
-	return cmd.dispatch()
+	return command.Dispatch(params, handler)
 }
 
 type commandHandler struct {
@@ -114,106 +115,12 @@
 	return runcmd()
 }
 
-func (c *commandHandler) dispatch() (interface{}, error) {
-	switch c.params.Command {
-	case source.CommandFillStruct.ID(), source.CommandUndeclaredName.ID(),
-		source.CommandExtractVariable.ID(), source.CommandExtractFunction.ID():
-		var uri protocol.DocumentURI
-		var rng protocol.Range
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &rng); err != nil {
-			return nil, err
-		}
-		err := c.ApplyFix(uri, rng)
-		return nil, err
-	case source.CommandTest.ID():
-		var uri protocol.DocumentURI
-		var tests, benchmarks []string
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &tests, &benchmarks); err != nil {
-			return nil, err
-		}
-		err := c.RunTests(uri, tests, benchmarks)
-		return nil, err
-	case source.CommandGenerate.ID():
-		var uri protocol.DocumentURI
-		var recursive bool
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &recursive); err != nil {
-			return nil, err
-		}
-		err := c.Generate(uri, recursive)
-		return nil, err
-	case source.CommandRegenerateCgo.ID():
-		var uri protocol.DocumentURI
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri); err != nil {
-			return nil, err
-		}
-		return nil, c.RegenerateCgo(uri)
-	case source.CommandTidy.ID():
-		var uri protocol.DocumentURI
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri); err != nil {
-			return nil, err
-		}
-		return nil, c.Tidy(uri)
-	case source.CommandVendor.ID():
-		var uri protocol.DocumentURI
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri); err != nil {
-			return nil, err
-		}
-		return nil, c.Vendor(uri)
-	case source.CommandUpdateGoSum.ID():
-		var uri protocol.DocumentURI
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri); err != nil {
-			return nil, err
-		}
-		return nil, c.UpdateGoSum(uri)
-	case source.CommandCheckUpgrades.ID():
-		var uri protocol.DocumentURI
-		var modules []string
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &modules); err != nil {
-			return nil, err
-		}
-		return nil, c.CheckUpgrades(uri, modules)
-	case source.CommandAddDependency.ID(), source.CommandUpgradeDependency.ID():
-		var uri protocol.DocumentURI
-		var goCmdArgs []string
-		var addRequire bool
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &addRequire, &goCmdArgs); err != nil {
-			return nil, err
-		}
-		return nil, c.GoGetModule(uri, addRequire, goCmdArgs)
-	case source.CommandRemoveDependency.ID():
-		var uri protocol.DocumentURI
-		var modulePath string
-		var onlyDiagnostic bool
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &onlyDiagnostic, &modulePath); err != nil {
-			return nil, err
-		}
-		return nil, c.RemoveDependency(modulePath, uri, onlyDiagnostic)
-	case source.CommandGoGetPackage.ID():
-		var uri protocol.DocumentURI
-		var pkg string
-		var addRequire bool
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri, &addRequire, &pkg); err != nil {
-			return nil, err
-		}
-		return nil, c.GoGetPackage(uri, addRequire, pkg)
-	case source.CommandToggleDetails.ID():
-		var uri protocol.DocumentURI
-		if err := source.UnmarshalArgs(c.params.Arguments, &uri); err != nil {
-			return nil, err
-		}
-		return nil, c.GCDetails(uri)
-	case source.CommandGenerateGoplsMod.ID():
-		return nil, c.GenerateGoplsMod()
-	}
-	return nil, fmt.Errorf("unsupported command: %s", c.params.Command)
-}
-
-func (c *commandHandler) ApplyFix(uri protocol.DocumentURI, rng protocol.Range) error {
+func (c *commandHandler) ApplyFix(args command.ApplyFixArgs) error {
 	return c.run(commandConfig{
 		// Note: no progress here. Applying fixes should be quick.
-		forURI: uri,
+		forURI: args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		edits, err := source.ApplyFix(ctx, c.params.Command, deps.snapshot, deps.fh, rng)
+		edits, err := source.ApplyFix(ctx, args.Fix, deps.snapshot, deps.fh, args.Range)
 		if err != nil {
 			return err
 		}
@@ -232,24 +139,24 @@
 	})
 }
 
-func (c *commandHandler) RegenerateCgo(uri protocol.DocumentURI) error {
+func (c *commandHandler) RegenerateCgo(args command.URIArg) error {
 	return c.run(commandConfig{
-		progress: source.CommandRegenerateCgo.Title,
+		progress: "Regenerating Cgo",
 	}, func(ctx context.Context, deps commandDeps) error {
 		mod := source.FileModification{
-			URI:    uri.SpanURI(),
+			URI:    args.URI.SpanURI(),
 			Action: source.InvalidateMetadata,
 		}
 		return c.s.didModifyFiles(c.ctx, []source.FileModification{mod}, FromRegenerateCgo)
 	})
 }
 
-func (c *commandHandler) CheckUpgrades(uri protocol.DocumentURI, modules []string) error {
+func (c *commandHandler) CheckUpgrades(args command.CheckUpgradesArgs) error {
 	return c.run(commandConfig{
-		forURI:   uri,
-		progress: source.CommandCheckUpgrades.Title,
+		forURI:   args.URI,
+		progress: "Checking for upgrades",
 	}, func(ctx context.Context, deps commandDeps) error {
-		upgrades, err := c.s.getUpgrades(ctx, deps.snapshot, uri.SpanURI(), modules)
+		upgrades, err := c.s.getUpgrades(ctx, deps.snapshot, args.URI.SpanURI(), args.Modules)
 		if err != nil {
 			return err
 		}
@@ -260,70 +167,78 @@
 	})
 }
 
-func (c *commandHandler) GoGetModule(uri protocol.DocumentURI, addRequire bool, goCmdArgs []string) error {
+func (c *commandHandler) AddDependency(args command.DependencyArgs) error {
+	return c.GoGetModule(args)
+}
+
+func (c *commandHandler) UpgradeDependency(args command.DependencyArgs) error {
+	return c.GoGetModule(args)
+}
+
+func (c *commandHandler) GoGetModule(args command.DependencyArgs) error {
 	return c.run(commandConfig{
 		requireSave: true,
 		progress:    "Running go get",
-		forURI:      uri,
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		return runGoGetModule(ctx, deps.snapshot, uri.SpanURI(), addRequire, goCmdArgs)
+		return runGoGetModule(ctx, deps.snapshot, args.URI.SpanURI(), args.AddRequire, args.GoCmdArgs)
 	})
 }
 
 // TODO(rFindley): UpdateGoSum, Tidy, and Vendor could probably all be one command.
 
-func (c *commandHandler) UpdateGoSum(uri protocol.DocumentURI) error {
+func (c *commandHandler) UpdateGoSum(args command.URIArg) error {
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandUpdateGoSum.Title,
-		forURI:      uri,
+		progress:    "Updating go.sum",
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, uri.SpanURI(), "list", []string{"all"})
+		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, args.URI.SpanURI(), "list", []string{"all"})
 	})
 }
 
-func (c *commandHandler) Tidy(uri protocol.DocumentURI) error {
+func (c *commandHandler) Tidy(args command.URIArg) error {
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandTidy.Title,
-		forURI:      uri,
+		progress:    "Running go mod tidy",
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, uri.SpanURI(), "mod", []string{"tidy"})
+		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, args.URI.SpanURI(), "mod", []string{"tidy"})
 	})
 }
 
-func (c *commandHandler) Vendor(uri protocol.DocumentURI) error {
+func (c *commandHandler) Vendor(args command.URIArg) error {
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandVendor.Title,
-		forURI:      uri,
+		progress:    "Running go mod vendor",
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, uri.SpanURI(), "mod", []string{"vendor"})
+		return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, args.URI.SpanURI(), "mod", []string{"vendor"})
 	})
 }
 
-func (c *commandHandler) RemoveDependency(modulePath string, uri protocol.DocumentURI, onlyDiagnostic bool) error {
+func (c *commandHandler) RemoveDependency(args command.RemoveDependencyArgs) error {
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandRemoveDependency.Title,
-		forURI:      uri,
+		progress:    "Removing dependency",
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
 		// If the module is tidied apart from the one unused diagnostic, we can
 		// run `go get module@none`, and then run `go mod tidy`. Otherwise, we
 		// must make textual edits.
 		// TODO(rstambler): In Go 1.17+, we will be able to use the go command
 		// without checking if the module is tidy.
-		if onlyDiagnostic {
-			if err := runGoGetModule(ctx, deps.snapshot, uri.SpanURI(), false, []string{modulePath + "@none"}); err != nil {
+		if args.OnlyDiagnostic {
+			if err := runGoGetModule(ctx, deps.snapshot, args.URI.SpanURI(), false, []string{args.ModulePath + "@none"}); err != nil {
 				return err
 			}
-			return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, uri.SpanURI(), "mod", []string{"tidy"})
+			return runSimpleGoCommand(ctx, deps.snapshot, source.UpdateUserModFile|source.AllowNetwork, args.URI.SpanURI(), "mod", []string{"tidy"})
 		}
 		pm, err := deps.snapshot.ParseMod(ctx, deps.fh)
 		if err != nil {
 			return err
 		}
-		edits, err := dropDependency(deps.snapshot, pm, modulePath)
+		edits, err := dropDependency(deps.snapshot, pm, args.ModulePath)
 		if err != nil {
 			return err
 		}
@@ -375,14 +290,22 @@
 	return source.ToProtocolEdits(pm.Mapper, diff)
 }
 
-func (c *commandHandler) RunTests(uri protocol.DocumentURI, tests, benchmarks []string) error {
+func (c *commandHandler) Test(uri protocol.DocumentURI, tests, benchmarks []string) error {
+	return c.RunTests(command.RunTestsArgs{
+		URI:        uri,
+		Tests:      tests,
+		Benchmarks: benchmarks,
+	})
+}
+
+func (c *commandHandler) RunTests(args command.RunTestsArgs) error {
 	return c.run(commandConfig{
 		async:       true,
-		progress:    source.CommandTest.Title,
+		progress:    "Running go test",
 		requireSave: true,
-		forURI:      uri,
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		if err := c.runTests(ctx, deps.snapshot, deps.work, uri, tests, benchmarks); err != nil {
+		if err := c.runTests(ctx, deps.snapshot, deps.work, args.URI, args.Tests, args.Benchmarks); err != nil {
 			if err := c.s.client.ShowMessage(ctx, &protocol.ShowMessageParams{
 				Type:    protocol.Error,
 				Message: fmt.Sprintf("Running tests failed: %v", err),
@@ -472,22 +395,26 @@
 	})
 }
 
-func (c *commandHandler) Generate(uri protocol.DocumentURI, recursive bool) error {
+func (c *commandHandler) Generate(args command.GenerateArgs) error {
+	title := "Running go generate ."
+	if args.Recursive {
+		title = "Running go generate ./..."
+	}
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandGenerate.Title,
-		forURI:      uri,
+		progress:    title,
+		forURI:      args.Dir,
 	}, func(ctx context.Context, deps commandDeps) error {
 		er := &eventWriter{ctx: ctx, operation: "generate"}
 
 		pattern := "."
-		if recursive {
+		if args.Recursive {
 			pattern = "./..."
 		}
 		inv := &gocommand.Invocation{
 			Verb:       "generate",
 			Args:       []string{"-x", pattern},
-			WorkingDir: uri.SpanURI().Filename(),
+			WorkingDir: args.Dir.SpanURI().Filename(),
 		}
 		stderr := io.MultiWriter(er, workDoneWriter{deps.work})
 		if err := deps.snapshot.RunGoCommandPiped(ctx, source.Normal, inv, er, stderr); err != nil {
@@ -497,22 +424,22 @@
 	})
 }
 
-func (c *commandHandler) GoGetPackage(puri protocol.DocumentURI, addRequire bool, pkg string) error {
+func (c *commandHandler) GoGetPackage(args command.GoGetPackageArgs) error {
 	return c.run(commandConfig{
-		forURI:   puri,
-		progress: source.CommandGoGetPackage.Title,
+		forURI:   args.URI,
+		progress: "Running go get",
 	}, func(ctx context.Context, deps commandDeps) error {
-		uri := puri.SpanURI()
+		uri := args.URI.SpanURI()
 		stdout, err := deps.snapshot.RunGoCommandDirect(ctx, source.WriteTemporaryModFile|source.AllowNetwork, &gocommand.Invocation{
 			Verb:       "list",
-			Args:       []string{"-f", "{{.Module.Path}}@{{.Module.Version}}", pkg},
+			Args:       []string{"-f", "{{.Module.Path}}@{{.Module.Version}}", args.Pkg},
 			WorkingDir: filepath.Dir(uri.Filename()),
 		})
 		if err != nil {
 			return err
 		}
 		ver := strings.TrimSpace(stdout.String())
-		return runGoGetModule(ctx, deps.snapshot, uri, addRequire, []string{ver})
+		return runGoGetModule(ctx, deps.snapshot, uri, args.AddRequire, []string{ver})
 	})
 }
 
@@ -563,12 +490,16 @@
 }
 
 func (c *commandHandler) GCDetails(uri protocol.DocumentURI) error {
+	return c.ToggleGCDetails(command.URIArg{URI: uri})
+}
+
+func (c *commandHandler) ToggleGCDetails(args command.URIArg) error {
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandToggleDetails.Title,
-		forURI:      uri,
+		progress:    "Toggling GC Details",
+		forURI:      args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		pkgDir := span.URIFromPath(filepath.Dir(uri.SpanURI().Filename()))
+		pkgDir := span.URIFromPath(filepath.Dir(args.URI.SpanURI().Filename()))
 		c.s.gcOptimizationDetailsMu.Lock()
 		if _, ok := c.s.gcOptimizationDetails[pkgDir]; ok {
 			delete(c.s.gcOptimizationDetails, pkgDir)
@@ -582,10 +513,11 @@
 	})
 }
 
-func (c *commandHandler) GenerateGoplsMod() error {
+func (c *commandHandler) GenerateGoplsMod(args command.URIArg) error {
+	// TODO: go back to using URI
 	return c.run(commandConfig{
 		requireSave: true,
-		progress:    source.CommandGenerateGoplsMod.Title,
+		progress:    "Generating gopls.mod",
 	}, func(ctx context.Context, deps commandDeps) error {
 		views := c.s.session.Views()
 		if len(views) != 1 {
diff --git a/internal/lsp/command/command_gen.go b/internal/lsp/command/command_gen.go
index d3dbfd5..2bd2170 100644
--- a/internal/lsp/command/command_gen.go
+++ b/internal/lsp/command/command_gen.go
@@ -16,6 +16,44 @@
 	"golang.org/x/tools/internal/lsp/protocol"
 )
 
+const (
+	AddDependency     Command = "add_dependency"
+	ApplyFix          Command = "apply_fix"
+	CheckUpgrades     Command = "check_upgrades"
+	GCDetails         Command = "gc_details"
+	Generate          Command = "generate"
+	GenerateGoplsMod  Command = "generate_gopls_mod"
+	GoGetPackage      Command = "go_get_package"
+	RegenerateCgo     Command = "regenerate_cgo"
+	RemoveDependency  Command = "remove_dependency"
+	RunTests          Command = "run_tests"
+	Test              Command = "test"
+	Tidy              Command = "tidy"
+	ToggleGCDetails   Command = "toggle_gc_details"
+	UpdateGoSum       Command = "update_go_sum"
+	UpgradeDependency Command = "upgrade_dependency"
+	Vendor            Command = "vendor"
+)
+
+var Commands = []Command{
+	AddDependency,
+	ApplyFix,
+	CheckUpgrades,
+	GCDetails,
+	Generate,
+	GenerateGoplsMod,
+	GoGetPackage,
+	RegenerateCgo,
+	RemoveDependency,
+	RunTests,
+	Test,
+	Tidy,
+	ToggleGCDetails,
+	UpdateGoSum,
+	UpgradeDependency,
+	Vendor,
+}
+
 func Dispatch(params *protocol.ExecuteCommandParams, s Interface) (interface{}, error) {
 	switch params.Command {
 	case "gopls.add_dependency":
@@ -25,6 +63,13 @@
 		}
 		err := s.AddDependency(a0)
 		return nil, err
+	case "gopls.apply_fix":
+		var a0 ApplyFixArgs
+		if err := UnmarshalArgs(params.Arguments, &a0); err != nil {
+			return nil, err
+		}
+		err := s.ApplyFix(a0)
+		return nil, err
 	case "gopls.check_upgrades":
 		var a0 CheckUpgradesArgs
 		if err := UnmarshalArgs(params.Arguments, &a0); err != nil {
@@ -33,7 +78,7 @@
 		err := s.CheckUpgrades(a0)
 		return nil, err
 	case "gopls.gc_details":
-		var a0 URIArg
+		var a0 protocol.DocumentURI
 		if err := UnmarshalArgs(params.Arguments, &a0); err != nil {
 			return nil, err
 		}
@@ -97,6 +142,13 @@
 		}
 		err := s.Tidy(a0)
 		return nil, err
+	case "gopls.toggle_gc_details":
+		var a0 URIArg
+		if err := UnmarshalArgs(params.Arguments, &a0); err != nil {
+			return nil, err
+		}
+		err := s.ToggleGCDetails(a0)
+		return nil, err
 	case "gopls.update_go_sum":
 		var a0 URIArg
 		if err := UnmarshalArgs(params.Arguments, &a0); err != nil {
@@ -134,6 +186,18 @@
 	}, nil
 }
 
+func NewApplyFixCommand(title string, a0 ApplyFixArgs) (protocol.Command, error) {
+	args, err := MarshalArgs(a0)
+	if err != nil {
+		return protocol.Command{}, err
+	}
+	return protocol.Command{
+		Title:     title,
+		Command:   "gopls.apply_fix",
+		Arguments: args,
+	}, nil
+}
+
 func NewCheckUpgradesCommand(title string, a0 CheckUpgradesArgs) (protocol.Command, error) {
 	args, err := MarshalArgs(a0)
 	if err != nil {
@@ -146,7 +210,7 @@
 	}, nil
 }
 
-func NewGCDetailsCommand(title string, a0 URIArg) (protocol.Command, error) {
+func NewGCDetailsCommand(title string, a0 protocol.DocumentURI) (protocol.Command, error) {
 	args, err := MarshalArgs(a0)
 	if err != nil {
 		return protocol.Command{}, err
@@ -254,6 +318,18 @@
 	}, nil
 }
 
+func NewToggleGCDetailsCommand(title string, a0 URIArg) (protocol.Command, error) {
+	args, err := MarshalArgs(a0)
+	if err != nil {
+		return protocol.Command{}, err
+	}
+	return protocol.Command{
+		Title:     title,
+		Command:   "gopls.toggle_gc_details",
+		Arguments: args,
+	}, nil
+}
+
 func NewUpdateGoSumCommand(title string, a0 URIArg) (protocol.Command, error) {
 	args, err := MarshalArgs(a0)
 	if err != nil {
diff --git a/internal/lsp/command/commandmeta/meta.go b/internal/lsp/command/commandmeta/meta.go
index 5c5e57c..70b1fe2 100644
--- a/internal/lsp/command/commandmeta/meta.go
+++ b/internal/lsp/command/commandmeta/meta.go
@@ -31,6 +31,10 @@
 	Result types.Type
 }
 
+func (c *Command) ID() string {
+	return command.ID(c.Name)
+}
+
 type Field struct {
 	Name    string
 	Doc     string
@@ -44,14 +48,18 @@
 func Load() (*packages.Package, []*Command, error) {
 	pkgs, err := packages.Load(
 		&packages.Config{
-			Mode: packages.NeedTypes | packages.NeedTypesInfo | packages.NeedSyntax | packages.NeedDeps,
+			Mode:       packages.NeedTypes | packages.NeedTypesInfo | packages.NeedSyntax | packages.NeedImports | packages.NeedDeps,
+			BuildFlags: []string{"-tags=generate"},
 		},
 		"golang.org/x/tools/internal/lsp/command",
 	)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, fmt.Errorf("packages.Load: %v", err)
 	}
 	pkg := pkgs[0]
+	if len(pkg.Errors) > 0 {
+		return pkg, nil, pkg.Errors[0]
+	}
 
 	// For a bit of type safety, use reflection to get the interface name within
 	// the package scope.
@@ -138,7 +146,10 @@
 			obj2 := s.Field(i)
 			pkg2 := pkg
 			if obj2.Pkg() != pkg2.Types {
-				pkg2 = pkg.Imports[obj2.Pkg().Path()]
+				pkg2, ok = pkg.Imports[obj2.Pkg().Path()]
+				if !ok {
+					return nil, fmt.Errorf("missing import for %q: %q", pkg.ID, obj2.Pkg().Path())
+				}
 			}
 			node2, err := findField(pkg2, obj2.Pos())
 			if err != nil {
@@ -160,7 +171,7 @@
 //
 // The doc comment should be of the form: "MethodName: Title\nDocumentation"
 func splitDoc(text string) (title, doc string) {
-	docParts := strings.SplitN(doc, "\n", 2)
+	docParts := strings.SplitN(text, "\n", 2)
 	titleParts := strings.SplitN(docParts[0], ":", 2)
 	if len(titleParts) > 1 {
 		title = strings.TrimSpace(titleParts[1])
@@ -177,7 +188,7 @@
 	for i := range words {
 		words[i] = strings.ToLower(words[i])
 	}
-	return "gopls." + strings.Join(words, "_")
+	return strings.Join(words, "_")
 }
 
 // splitCamel splits s into words, according to camel-case word boundaries.
diff --git a/internal/lsp/command/generate/generate.go b/internal/lsp/command/generate/generate.go
index d31b437..eb24bbd 100644
--- a/internal/lsp/command/generate/generate.go
+++ b/internal/lsp/command/generate/generate.go
@@ -34,10 +34,22 @@
 	{{end}}
 )
 
+const (
+{{- range .Commands}}
+	{{.MethodName}} Command = "{{.Name}}"
+{{- end}}
+)
+
+var Commands = []Command {
+{{- range .Commands}}
+	{{.MethodName}},
+{{- end}}
+}
+
 func Dispatch(params *protocol.ExecuteCommandParams, s Interface) (interface{}, error) {
 	switch params.Command {
 	{{- range .Commands}}
-	case "{{.Name}}":
+	case "{{.ID}}":
 		{{- if .Args -}}
 			{{- range $i, $v := .Args}}
 		var a{{$i}} {{typeString $v.Type}}
@@ -61,7 +73,7 @@
 	}
 	return protocol.Command{
 		Title: title,
-		Command: "{{.Name}}",
+		Command: "{{.ID}}",
 		Arguments: args,
 	}, nil
 }
@@ -76,7 +88,7 @@
 func Generate() ([]byte, error) {
 	pkg, cmds, err := commandmeta.Load()
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("loading command data: %v", err)
 	}
 	qf := func(p *types.Package) string {
 		if p == pkg.Types {
diff --git a/internal/lsp/command/interface.go b/internal/lsp/command/interface.go
index 4f068fa..bc08526 100644
--- a/internal/lsp/command/interface.go
+++ b/internal/lsp/command/interface.go
@@ -28,11 +28,17 @@
 //     is considered the command 'Title'.
 //     TODO(rFindley): reconsider this -- Title may be unnecessary.
 type Interface interface {
+	// ApplyFix: Apply a fix
+	//
+	// Applies a fix to a region of source code.
+	ApplyFix(ApplyFixArgs) error
 	// Test: Run test(s) (legacy)
 	//
-	// Deprecated: use gopls.run_tests.
+	// Runs `go test` for a specific set of test or benchmark functions.
 	Test(protocol.DocumentURI, []string, []string) error
 
+	// TODO: deprecate Test in favor of RunTests below.
+
 	// Test: Run test(s)
 	//
 	// Runs `go test` for a specific set of test or benchmark functions.
@@ -91,7 +97,14 @@
 	// GCDetails: Toggle gc_details
 	//
 	// Toggle the calculation of gc annotations.
-	GCDetails(URIArg) error
+	GCDetails(protocol.DocumentURI) error
+
+	// TODO: deprecate GCDetails in favor of ToggleGCDetails below.
+
+	// ToggleGCDetails: Toggle gc_details
+	//
+	// Toggle the calculation of gc annotations.
+	ToggleGCDetails(URIArg) error
 
 	// GenerateGoplsMod: Generate gopls.mod
 	//
@@ -111,9 +124,8 @@
 }
 
 type GenerateArgs struct {
-	// URI is any file within the directory to generate. Usually this is the file
-	// containing the '//go:generate' directive.
-	URI protocol.DocumentURI
+	// Dir is the directory to generate.
+	Dir protocol.DocumentURI
 
 	// Recursive controls whether to generate recursively (go generate ./...)
 	Recursive bool
@@ -121,6 +133,12 @@
 
 // TODO(rFindley): document the rest of these once the docgen is fleshed out.
 
+type ApplyFixArgs struct {
+	Fix   string
+	URI   protocol.DocumentURI
+	Range protocol.Range
+}
+
 type URIArg struct {
 	URI protocol.DocumentURI
 }
@@ -143,6 +161,7 @@
 }
 
 type GoGetPackageArgs struct {
-	URI protocol.DocumentURI
-	Pkg string
+	URI        protocol.DocumentURI
+	Pkg        string
+	AddRequire bool
 }
diff --git a/internal/lsp/command/util.go b/internal/lsp/command/util.go
index c81aaf6..5915b9b 100644
--- a/internal/lsp/command/util.go
+++ b/internal/lsp/command/util.go
@@ -9,6 +9,17 @@
 	"fmt"
 )
 
+// ID returns the command name for use in the LSP.
+func ID(name string) string {
+	return "gopls." + name
+}
+
+type Command string
+
+func (c Command) ID() string {
+	return ID(string(c))
+}
+
 // MarshalArgs encodes the given arguments to json.RawMessages. This function
 // is used to construct arguments to a protocol.Command.
 //
diff --git a/internal/lsp/fake/editor.go b/internal/lsp/fake/editor.go
index 9bd2028..ea77ffa 100644
--- a/internal/lsp/fake/editor.go
+++ b/internal/lsp/fake/editor.go
@@ -15,8 +15,8 @@
 	"sync"
 
 	"golang.org/x/tools/internal/jsonrpc2"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
-	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
 	errors "golang.org/x/xerrors"
 )
@@ -892,18 +892,22 @@
 // path. It does not report any resulting file changes as a watched file
 // change, so must be followed by a call to Workdir.CheckForFileChanges once
 // the generate command has completed.
+// TODO(rFindley): this shouldn't be necessary anymore. Delete it.
 func (e *Editor) RunGenerate(ctx context.Context, dir string) error {
 	if e.Server == nil {
 		return nil
 	}
 	absDir := e.sandbox.Workdir.AbsPath(dir)
-	jsonArgs, err := source.MarshalArgs(span.URIFromPath(absDir), false)
+	cmd, err := command.NewGenerateCommand("", command.GenerateArgs{
+		Dir:       protocol.URIFromSpanURI(span.URIFromPath(absDir)),
+		Recursive: false,
+	})
 	if err != nil {
 		return err
 	}
 	params := &protocol.ExecuteCommandParams{
-		Command:   source.CommandGenerate.ID(),
-		Arguments: jsonArgs,
+		Command:   cmd.Command,
+		Arguments: cmd.Arguments,
 	}
 	if _, err := e.ExecuteCommand(ctx, params); err != nil {
 		return fmt.Errorf("running generate: %v", err)
diff --git a/internal/lsp/lsp_test.go b/internal/lsp/lsp_test.go
index 2318b04..2b82891 100644
--- a/internal/lsp/lsp_test.go
+++ b/internal/lsp/lsp_test.go
@@ -40,6 +40,7 @@
 	diagnostics map[span.URI][]*source.Diagnostic
 	ctx         context.Context
 	normalizers []tests.Normalizer
+	editRecv    chan map[span.URI]string
 }
 
 func testLSP(t *testing.T, datum *tests.Data) {
@@ -85,17 +86,19 @@
 		t.Fatal(err)
 	}
 	r := &runner{
-		server:      NewServer(session, testClient{}),
 		data:        datum,
 		ctx:         ctx,
 		normalizers: tests.CollectNormalizers(datum.Exported),
+		editRecv:    make(chan map[span.URI]string, 1),
 	}
+	r.server = NewServer(session, testClient{runner: r})
 	tests.Run(t, r, datum)
 }
 
 // testClient stubs any client functions that may be called by LSP functions.
 type testClient struct {
 	protocol.Client
+	runner *runner
 }
 
 // Trivially implement PublishDiagnostics so that we can call
@@ -104,6 +107,15 @@
 	return nil
 }
 
+func (c testClient) ApplyEdit(ctx context.Context, params *protocol.ApplyWorkspaceEditParams) (*protocol.ApplyWorkspaceEditResponse, error) {
+	res, err := applyTextDocumentEdits(c.runner, params.Edit.DocumentChanges)
+	if err != nil {
+		return nil, err
+	}
+	c.runner.editRecv <- res
+	return &protocol.ApplyWorkspaceEditResponse{Applied: true}, nil
+}
+
 func (r *runner) CallHierarchy(t *testing.T, spn span.Span, expectedCalls *tests.CallHierarchyResult) {
 	mapper, err := r.data.Mapper(spn.URI())
 	if err != nil {
@@ -468,13 +480,6 @@
 		t.Fatal(err)
 	}
 
-	snapshot, release := view.Snapshot(r.ctx)
-	defer release()
-
-	fh, err := snapshot.GetVersionedFile(r.ctx, uri)
-	if err != nil {
-		t.Fatal(err)
-	}
 	m, err := r.data.Mapper(uri)
 	if err != nil {
 		t.Fatal(err)
@@ -533,14 +538,14 @@
 	}
 	var res map[span.URI]string
 	if cmd := action.Command; cmd != nil {
-		edits, err := source.ApplyFix(r.ctx, cmd.Command, snapshot, fh, rng)
+		_, err := r.server.ExecuteCommand(r.ctx, &protocol.ExecuteCommandParams{
+			Command:   action.Command.Command,
+			Arguments: action.Command.Arguments,
+		})
 		if err != nil {
 			t.Fatalf("error converting command %q to edits: %v", action.Command.Command, err)
 		}
-		res, err = applyTextDocumentEdits(r, edits)
-		if err != nil {
-			t.Fatal(err)
-		}
+		res = <-r.editRecv
 	} else {
 		res, err = applyTextDocumentEdits(r, action.Edit.DocumentChanges)
 		if err != nil {
@@ -559,18 +564,6 @@
 
 func (r *runner) FunctionExtraction(t *testing.T, start span.Span, end span.Span) {
 	uri := start.URI()
-	view, err := r.server.session.ViewOf(uri)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	snapshot, release := view.Snapshot(r.ctx)
-	defer release()
-
-	fh, err := snapshot.GetVersionedFile(r.ctx, uri)
-	if err != nil {
-		t.Fatal(err)
-	}
 	m, err := r.data.Mapper(uri)
 	if err != nil {
 		t.Fatal(err)
@@ -597,14 +590,14 @@
 	if len(actions) == 0 || len(actions) > 1 {
 		t.Fatalf("unexpected number of code actions, want 1, got %v", len(actions))
 	}
-	edits, err := source.ApplyFix(r.ctx, actions[0].Command.Command, snapshot, fh, rng)
+	_, err = r.server.ExecuteCommand(r.ctx, &protocol.ExecuteCommandParams{
+		Command:   actions[0].Command.Command,
+		Arguments: actions[0].Command.Arguments,
+	})
 	if err != nil {
 		t.Fatal(err)
 	}
-	res, err := applyTextDocumentEdits(r, edits)
-	if err != nil {
-		t.Fatal(err)
-	}
+	res := <-r.editRecv
 	for u, got := range res {
 		want := string(r.data.Golden("functionextraction_"+tests.SpanName(spn), u.Filename(), func() ([]byte, error) {
 			return []byte(got), nil
diff --git a/internal/lsp/mod/code_lens.go b/internal/lsp/mod/code_lens.go
index 88ffe84..f66a3e1 100644
--- a/internal/lsp/mod/code_lens.go
+++ b/internal/lsp/mod/code_lens.go
@@ -11,17 +11,18 @@
 	"path/filepath"
 
 	"golang.org/x/mod/modfile"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
 )
 
 // LensFuncs returns the supported lensFuncs for go.mod files.
-func LensFuncs() map[string]source.LensFunc {
-	return map[string]source.LensFunc{
-		source.CommandUpgradeDependency.Name: upgradeLenses,
-		source.CommandTidy.Name:              tidyLens,
-		source.CommandVendor.Name:            vendorLens,
+func LensFuncs() map[command.Command]source.LensFunc {
+	return map[command.Command]source.LensFunc{
+		command.UpgradeDependency: upgradeLenses,
+		command.Tidy:              tidyLens,
+		command.Vendor:            vendorLens,
 	}
 }
 
@@ -34,19 +35,31 @@
 		// Nothing to upgrade.
 		return nil, nil
 	}
-	upgradeTransitiveArgs, err := source.MarshalArgs(fh.URI(), false, []string{"-u", "all"})
-	if err != nil {
-		return nil, err
-	}
 	var requires []string
 	for _, req := range pm.File.Require {
 		requires = append(requires, req.Mod.Path)
 	}
-	checkUpgradeArgs, err := source.MarshalArgs(fh.URI(), requires)
+	uri := protocol.URIFromSpanURI(fh.URI())
+	checkUpgrade, err := command.NewCheckUpgradesCommand("Check for upgrades", command.CheckUpgradesArgs{
+		URI:     uri,
+		Modules: requires,
+	})
 	if err != nil {
 		return nil, err
 	}
-	upgradeDirectArgs, err := source.MarshalArgs(fh.URI(), false, requires)
+	upgradeTransitive, err := command.NewUpgradeDependencyCommand("Upgrade transitive dependencies", command.DependencyArgs{
+		URI:        uri,
+		AddRequire: false,
+		GoCmdArgs:  []string{"-u", "all"},
+	})
+	if err != nil {
+		return nil, err
+	}
+	upgradeDirect, err := command.NewUpgradeDependencyCommand("Upgrade direct dependencies", command.DependencyArgs{
+		URI:        uri,
+		AddRequire: false,
+		GoCmdArgs:  requires,
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -57,30 +70,9 @@
 	}
 
 	return []protocol.CodeLens{
-		{
-			Range: rng,
-			Command: protocol.Command{
-				Title:     "Check for upgrades",
-				Command:   source.CommandCheckUpgrades.ID(),
-				Arguments: checkUpgradeArgs,
-			},
-		},
-		{
-			Range: rng,
-			Command: protocol.Command{
-				Title:     "Upgrade transitive dependencies",
-				Command:   source.CommandUpgradeDependency.ID(),
-				Arguments: upgradeTransitiveArgs,
-			},
-		},
-		{
-			Range: rng,
-			Command: protocol.Command{
-				Title:     "Upgrade direct dependencies",
-				Command:   source.CommandUpgradeDependency.ID(),
-				Arguments: upgradeDirectArgs,
-			},
-		},
+		{Range: rng, Command: checkUpgrade},
+		{Range: rng, Command: upgradeTransitive},
+		{Range: rng, Command: upgradeDirect},
 	}, nil
 }
 
@@ -93,7 +85,8 @@
 		// Nothing to vendor.
 		return nil, nil
 	}
-	goModArgs, err := source.MarshalArgs(fh.URI())
+	uri := protocol.URIFromSpanURI(fh.URI())
+	cmd, err := command.NewTidyCommand("Run go mod tidy", command.URIArg{URI: uri})
 	if err != nil {
 		return nil, err
 	}
@@ -102,12 +95,8 @@
 		return nil, err
 	}
 	return []protocol.CodeLens{{
-		Range: rng,
-		Command: protocol.Command{
-			Title:     source.CommandTidy.Title,
-			Command:   source.CommandTidy.ID(),
-			Arguments: goModArgs,
-		},
+		Range:   rng,
+		Command: cmd,
 	}}, nil
 }
 
@@ -120,25 +109,19 @@
 	if err != nil {
 		return nil, err
 	}
-	goModArgs, err := source.MarshalArgs(fh.URI())
+	title := "Create vendor directory"
+	uri := protocol.URIFromSpanURI(fh.URI())
+	cmd, err := command.NewVendorCommand(title, command.URIArg{URI: uri})
 	if err != nil {
 		return nil, err
 	}
 	// Change the message depending on whether or not the module already has a
 	// vendor directory.
-	title := "Create vendor directory"
 	vendorDir := filepath.Join(filepath.Dir(fh.URI().Filename()), "vendor")
 	if info, _ := os.Stat(vendorDir); info != nil && info.IsDir() {
 		title = "Sync vendor directory"
 	}
-	return []protocol.CodeLens{{
-		Range: rng,
-		Command: protocol.Command{
-			Title:     title,
-			Command:   source.CommandVendor.ID(),
-			Arguments: goModArgs,
-		},
-	}}, nil
+	return []protocol.CodeLens{{Range: rng, Command: cmd}}, nil
 }
 
 func moduleStmtRange(fh source.FileHandle, pm *source.ParsedModule) (protocol.Range, error) {
diff --git a/internal/lsp/mod/diagnostics.go b/internal/lsp/mod/diagnostics.go
index dcd641e..041bf72 100644
--- a/internal/lsp/mod/diagnostics.go
+++ b/internal/lsp/mod/diagnostics.go
@@ -11,6 +11,7 @@
 	"fmt"
 
 	"golang.org/x/tools/internal/event"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
@@ -65,24 +66,22 @@
 			return nil, err
 		}
 		// Upgrade to the exact version we offer the user, not the most recent.
-		args, err := source.MarshalArgs(fh.URI(), false, []string{req.Mod.Path + "@" + ver})
+		title := fmt.Sprintf("Upgrade to %v", ver)
+		cmd, err := command.NewUpgradeDependencyCommand(title, command.DependencyArgs{
+			URI:        protocol.URIFromSpanURI(fh.URI()),
+			AddRequire: false,
+			GoCmdArgs:  []string{req.Mod.Path + "@" + ver},
+		})
 		if err != nil {
 			return nil, err
 		}
 		diagnostics = append(diagnostics, &source.Diagnostic{
-			URI:      fh.URI(),
-			Range:    rng,
-			Severity: protocol.SeverityInformation,
-			Source:   source.UpgradeNotification,
-			Message:  fmt.Sprintf("%v can be upgraded", req.Mod.Path),
-			SuggestedFixes: []source.SuggestedFix{{
-				Title: fmt.Sprintf("Upgrade to %v", ver),
-				Command: &protocol.Command{
-					Title:     fmt.Sprintf("Upgrade to %v", ver),
-					Command:   source.CommandUpgradeDependency.ID(),
-					Arguments: args,
-				},
-			}},
+			URI:            fh.URI(),
+			Range:          rng,
+			Severity:       protocol.SeverityInformation,
+			Source:         source.UpgradeNotification,
+			Message:        fmt.Sprintf("%v can be upgraded", req.Mod.Path),
+			SuggestedFixes: []source.SuggestedFix{source.SuggestedFixFromCommand(cmd)},
 		})
 	}
 
diff --git a/internal/lsp/source/api_json.go b/internal/lsp/source/api_json.go
index 8a13428..1da2ccd 100755
--- a/internal/lsp/source/api_json.go
+++ b/internal/lsp/source/api_json.go
@@ -577,37 +577,37 @@
 					Keys: []EnumKey{
 						{
 							Name:    "\"gc_details\"",
-							Doc:     "gc_details controls calculation of gc annotations.\n",
+							Doc:     "Toggle the calculation of gc annotations.",
 							Default: "false",
 						},
 						{
 							Name:    "\"generate\"",
-							Doc:     "generate runs `go generate` for a given directory.\n",
+							Doc:     "Runs `go generate` for a given directory.",
 							Default: "true",
 						},
 						{
 							Name:    "\"regenerate_cgo\"",
-							Doc:     "regenerate_cgo regenerates cgo definitions.\n",
+							Doc:     "Regenerates cgo definitions.",
 							Default: "true",
 						},
 						{
 							Name:    "\"test\"",
-							Doc:     "test runs `go test` for a specific test function.\n",
+							Doc:     "Runs `go test` for a specific set of test or benchmark functions.",
 							Default: "false",
 						},
 						{
 							Name:    "\"tidy\"",
-							Doc:     "tidy runs `go mod tidy` for a module.\n",
+							Doc:     "Runs `go mod tidy` for a module.",
 							Default: "true",
 						},
 						{
 							Name:    "\"upgrade_dependency\"",
-							Doc:     "upgrade_dependency upgrades a dependency.\n",
+							Doc:     "Upgrades a dependency in the go.mod file for a module.",
 							Default: "true",
 						},
 						{
 							Name:    "\"vendor\"",
-							Doc:     "vendor runs `go mod vendor` for a module.\n",
+							Doc:     "Runs `go mod vendor` for a module.",
 							Default: "true",
 						},
 					},
@@ -675,124 +675,119 @@
 		{
 			Command: "gopls.add_dependency",
 			Title:   "Add dependency",
-			Doc:     "add_dependency adds a dependency.\n",
+			Doc:     "Adds a dependency to the go.mod file for a module.",
+		},
+		{
+			Command: "gopls.apply_fix",
+			Title:   "Apply a fix",
+			Doc:     "Applies a fix to a region of source code.",
 		},
 		{
 			Command: "gopls.check_upgrades",
 			Title:   "Check for upgrades",
-			Doc:     "check_upgrades checks for module upgrades.\n",
-		},
-		{
-			Command: "gopls.extract_function",
-			Title:   "Extract to function",
-			Doc:     "extract_function extracts statements to a function.\n",
-		},
-		{
-			Command: "gopls.extract_variable",
-			Title:   "Extract to variable",
-			Doc:     "extract_variable extracts an expression to a variable.\n",
-		},
-		{
-			Command: "gopls.fill_struct",
-			Title:   "Fill struct",
-			Doc:     "fill_struct is a gopls command to fill a struct with default\nvalues.\n",
+			Doc:     "Checks for module upgrades.",
 		},
 		{
 			Command: "gopls.gc_details",
 			Title:   "Toggle gc_details",
-			Doc:     "gc_details controls calculation of gc annotations.\n",
+			Doc:     "Toggle the calculation of gc annotations.",
 		},
 		{
 			Command: "gopls.generate",
 			Title:   "Run go generate",
-			Doc:     "generate runs `go generate` for a given directory.\n",
+			Doc:     "Runs `go generate` for a given directory.",
 		},
 		{
 			Command: "gopls.generate_gopls_mod",
 			Title:   "Generate gopls.mod",
-			Doc:     "generate_gopls_mod (re)generates the gopls.mod file.\n",
+			Doc:     "(Re)generate the gopls.mod file for a workspace.",
 		},
 		{
 			Command: "gopls.go_get_package",
 			Title:   "go get package",
-			Doc:     "go_get_package runs `go get` to fetch a package.\n",
+			Doc:     "Runs `go get` to fetch a package.",
 		},
 		{
 			Command: "gopls.regenerate_cgo",
 			Title:   "Regenerate cgo",
-			Doc:     "regenerate_cgo regenerates cgo definitions.\n",
+			Doc:     "Regenerates cgo definitions.",
 		},
 		{
 			Command: "gopls.remove_dependency",
 			Title:   "Remove dependency",
-			Doc:     "remove_dependency removes a dependency.\n",
+			Doc:     "Removes a dependency from the go.mod file of a module.",
+		},
+		{
+			Command: "gopls.run_tests",
+			Title:   "Run test(s)",
+			Doc:     "Runs `go test` for a specific set of test or benchmark functions.",
 		},
 		{
 			Command: "gopls.test",
-			Title:   "Run test(s)",
-			Doc:     "test runs `go test` for a specific test function.\n",
+			Title:   "Run test(s) (legacy)",
+			Doc:     "Runs `go test` for a specific set of test or benchmark functions.",
 		},
 		{
 			Command: "gopls.tidy",
 			Title:   "Run go mod tidy",
-			Doc:     "tidy runs `go mod tidy` for a module.\n",
+			Doc:     "Runs `go mod tidy` for a module.",
 		},
 		{
-			Command: "gopls.undeclared_name",
-			Title:   "Undeclared name",
-			Doc:     "undeclared_name adds a variable declaration for an undeclared\nname.\n",
+			Command: "gopls.toggle_gc_details",
+			Title:   "Toggle gc_details",
+			Doc:     "Toggle the calculation of gc annotations.",
 		},
 		{
 			Command: "gopls.update_go_sum",
 			Title:   "Update go.sum",
-			Doc:     "update_go_sum updates the go.sum file for a module.\n",
+			Doc:     "Updates the go.sum file for a module.",
 		},
 		{
 			Command: "gopls.upgrade_dependency",
 			Title:   "Upgrade dependency",
-			Doc:     "upgrade_dependency upgrades a dependency.\n",
+			Doc:     "Upgrades a dependency in the go.mod file for a module.",
 		},
 		{
 			Command: "gopls.vendor",
 			Title:   "Run go mod vendor",
-			Doc:     "vendor runs `go mod vendor` for a module.\n",
+			Doc:     "Runs `go mod vendor` for a module.",
 		},
 	},
 	Lenses: []*LensJSON{
 		{
 			Lens:  "gc_details",
 			Title: "Toggle gc_details",
-			Doc:   "gc_details controls calculation of gc annotations.\n",
+			Doc:   "Toggle the calculation of gc annotations.",
 		},
 		{
 			Lens:  "generate",
 			Title: "Run go generate",
-			Doc:   "generate runs `go generate` for a given directory.\n",
+			Doc:   "Runs `go generate` for a given directory.",
 		},
 		{
 			Lens:  "regenerate_cgo",
 			Title: "Regenerate cgo",
-			Doc:   "regenerate_cgo regenerates cgo definitions.\n",
+			Doc:   "Regenerates cgo definitions.",
 		},
 		{
 			Lens:  "test",
-			Title: "Run test(s)",
-			Doc:   "test runs `go test` for a specific test function.\n",
+			Title: "Run test(s) (legacy)",
+			Doc:   "Runs `go test` for a specific set of test or benchmark functions.",
 		},
 		{
 			Lens:  "tidy",
 			Title: "Run go mod tidy",
-			Doc:   "tidy runs `go mod tidy` for a module.\n",
+			Doc:   "Runs `go mod tidy` for a module.",
 		},
 		{
 			Lens:  "upgrade_dependency",
 			Title: "Upgrade dependency",
-			Doc:   "upgrade_dependency upgrades a dependency.\n",
+			Doc:   "Upgrades a dependency in the go.mod file for a module.",
 		},
 		{
 			Lens:  "vendor",
 			Title: "Run go mod vendor",
-			Doc:   "vendor runs `go mod vendor` for a module.\n",
+			Doc:   "Runs `go mod vendor` for a module.",
 		},
 	},
 	Analyzers: []*AnalyzerJSON{
diff --git a/internal/lsp/source/code_lens.go b/internal/lsp/source/code_lens.go
index 1dd66b4..0ab857a 100644
--- a/internal/lsp/source/code_lens.go
+++ b/internal/lsp/source/code_lens.go
@@ -13,6 +13,7 @@
 	"regexp"
 	"strings"
 
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
 )
@@ -20,12 +21,12 @@
 type LensFunc func(context.Context, Snapshot, FileHandle) ([]protocol.CodeLens, error)
 
 // LensFuncs returns the supported lensFuncs for Go files.
-func LensFuncs() map[string]LensFunc {
-	return map[string]LensFunc{
-		CommandGenerate.Name:      goGenerateCodeLens,
-		CommandTest.Name:          runTestCodeLens,
-		CommandRegenerateCgo.Name: regenerateCgoLens,
-		CommandToggleDetails.Name: toggleDetailsCodeLens,
+func LensFuncs() map[command.Command]LensFunc {
+	return map[command.Command]LensFunc{
+		command.Generate:      goGenerateCodeLens,
+		command.Test:          runTestCodeLens,
+		command.RegenerateCgo: regenerateCgoLens,
+		command.GCDetails:     toggleDetailsCodeLens,
 	}
 }
 
@@ -41,34 +42,23 @@
 	if err != nil {
 		return nil, err
 	}
+	puri := protocol.URIFromSpanURI(fh.URI())
 	for _, fn := range fns.Tests {
-		jsonArgs, err := MarshalArgs(fh.URI(), []string{fn.Name}, nil)
+		cmd, err := command.NewTestCommand("run test", puri, []string{fn.Name}, nil)
 		if err != nil {
 			return nil, err
 		}
-		codeLens = append(codeLens, protocol.CodeLens{
-			Range: protocol.Range{Start: fn.Rng.Start, End: fn.Rng.Start},
-			Command: protocol.Command{
-				Title:     "run test",
-				Command:   CommandTest.ID(),
-				Arguments: jsonArgs,
-			},
-		})
+		rng := protocol.Range{Start: fn.Rng.Start, End: fn.Rng.Start}
+		codeLens = append(codeLens, protocol.CodeLens{Range: rng, Command: cmd})
 	}
 
 	for _, fn := range fns.Benchmarks {
-		jsonArgs, err := MarshalArgs(fh.URI(), nil, []string{fn.Name})
+		cmd, err := command.NewTestCommand("run benchmark", puri, nil, []string{fn.Name})
 		if err != nil {
 			return nil, err
 		}
-		codeLens = append(codeLens, protocol.CodeLens{
-			Range: protocol.Range{Start: fn.Rng.Start, End: fn.Rng.Start},
-			Command: protocol.Command{
-				Title:     "run benchmark",
-				Command:   CommandTest.ID(),
-				Arguments: jsonArgs,
-			},
-		})
+		rng := protocol.Range{Start: fn.Rng.Start, End: fn.Rng.Start}
+		codeLens = append(codeLens, protocol.CodeLens{Range: rng, Command: cmd})
 	}
 
 	if len(fns.Benchmarks) > 0 {
@@ -81,18 +71,15 @@
 		if err != nil {
 			return nil, err
 		}
-		args, err := MarshalArgs(fh.URI(), []string{}, fns.Benchmarks)
+		var benches []string
+		for _, fn := range fns.Benchmarks {
+			benches = append(benches, fn.Name)
+		}
+		cmd, err := command.NewTestCommand("run file benchmarks", puri, nil, benches)
 		if err != nil {
 			return nil, err
 		}
-		codeLens = append(codeLens, protocol.CodeLens{
-			Range: rng,
-			Command: protocol.Command{
-				Title:     "run file benchmarks",
-				Command:   CommandTest.ID(),
-				Arguments: args,
-			},
-		})
+		codeLens = append(codeLens, protocol.CodeLens{Range: rng, Command: cmd})
 	}
 	return codeLens, nil
 }
@@ -194,32 +181,18 @@
 			if err != nil {
 				return nil, err
 			}
-			dir := span.URIFromPath(filepath.Dir(fh.URI().Filename()))
-			nonRecursiveArgs, err := MarshalArgs(dir, false)
+			dir := protocol.URIFromSpanURI(span.URIFromPath(filepath.Dir(fh.URI().Filename())))
+			nonRecursiveCmd, err := command.NewGenerateCommand("run go generate", command.GenerateArgs{Dir: dir, Recursive: false})
 			if err != nil {
 				return nil, err
 			}
-			recursiveArgs, err := MarshalArgs(dir, true)
+			recursiveCmd, err := command.NewGenerateCommand("run go generate ./...", command.GenerateArgs{Dir: dir, Recursive: true})
 			if err != nil {
 				return nil, err
 			}
 			return []protocol.CodeLens{
-				{
-					Range: rng,
-					Command: protocol.Command{
-						Title:     "run go generate",
-						Command:   CommandGenerate.ID(),
-						Arguments: nonRecursiveArgs,
-					},
-				},
-				{
-					Range: rng,
-					Command: protocol.Command{
-						Title:     "run go generate ./...",
-						Command:   CommandGenerate.ID(),
-						Arguments: recursiveArgs,
-					},
-				},
+				{Range: rng, Command: recursiveCmd},
+				{Range: rng, Command: nonRecursiveCmd},
 			}, nil
 
 		}
@@ -245,20 +218,12 @@
 	if err != nil {
 		return nil, err
 	}
-	jsonArgs, err := MarshalArgs(fh.URI())
+	puri := protocol.URIFromSpanURI(fh.URI())
+	cmd, err := command.NewRegenerateCgoCommand("regenerate cgo definitions", command.URIArg{URI: puri})
 	if err != nil {
 		return nil, err
 	}
-	return []protocol.CodeLens{
-		{
-			Range: rng,
-			Command: protocol.Command{
-				Title:     "regenerate cgo definitions",
-				Command:   CommandRegenerateCgo.ID(),
-				Arguments: jsonArgs,
-			},
-		},
-	}, nil
+	return []protocol.CodeLens{{Range: rng, Command: cmd}}, nil
 }
 
 func toggleDetailsCodeLens(ctx context.Context, snapshot Snapshot, fh FileHandle) ([]protocol.CodeLens, error) {
@@ -270,16 +235,10 @@
 	if err != nil {
 		return nil, err
 	}
-	jsonArgs, err := MarshalArgs(fh.URI())
+	puri := protocol.URIFromSpanURI(fh.URI())
+	cmd, err := command.NewGCDetailsCommand("Toggle gc annotation details", puri)
 	if err != nil {
 		return nil, err
 	}
-	return []protocol.CodeLens{{
-		Range: rng,
-		Command: protocol.Command{
-			Title:     "Toggle gc annotation details",
-			Command:   CommandToggleDetails.ID(),
-			Arguments: jsonArgs,
-		},
-	}}, nil
+	return []protocol.CodeLens{{Range: rng, Command: cmd}}, nil
 }
diff --git a/internal/lsp/source/command.go b/internal/lsp/source/command.go
deleted file mode 100644
index 1edf154..0000000
--- a/internal/lsp/source/command.go
+++ /dev/null
@@ -1,243 +0,0 @@
-// Copyright 2020 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package source
-
-import (
-	"context"
-	"fmt"
-	"go/ast"
-	"go/token"
-	"go/types"
-
-	"golang.org/x/tools/go/analysis"
-	"golang.org/x/tools/internal/lsp/analysis/fillstruct"
-	"golang.org/x/tools/internal/lsp/analysis/undeclaredname"
-	"golang.org/x/tools/internal/lsp/protocol"
-	"golang.org/x/tools/internal/span"
-	errors "golang.org/x/xerrors"
-)
-
-type Command struct {
-	Title string
-	Name  string
-
-	// Async controls whether the command executes asynchronously.
-	Async bool
-}
-
-// CommandPrefix is the prefix of all command names gopls uses externally.
-const CommandPrefix = "gopls."
-
-// ID adds the CommandPrefix to the command name, in order to avoid
-// collisions with other language servers.
-func (c Command) ID() string {
-	return CommandPrefix + c.Name
-}
-
-// SuggestedFixFunc is a function used to get the suggested fixes for a given
-// gopls command, some of which are provided by go/analysis.Analyzers. Some of
-// the analyzers in internal/lsp/analysis are not efficient enough to include
-// suggested fixes with their diagnostics, so we have to compute them
-// separately. Such analyzers should provide a function with a signature of
-// SuggestedFixFunc.
-type SuggestedFixFunc func(fset *token.FileSet, rng span.Range, src []byte, file *ast.File, pkg *types.Package, info *types.Info) (*analysis.SuggestedFix, error)
-
-// Commands are the commands currently supported by gopls.
-var Commands = []*Command{
-	CommandAddDependency,
-	CommandCheckUpgrades,
-	CommandExtractFunction,
-	CommandExtractVariable,
-	CommandFillStruct,
-	CommandToggleDetails, // gc_details
-	CommandGenerate,
-	CommandGenerateGoplsMod,
-	CommandGoGetPackage,
-	CommandRegenerateCgo,
-	CommandRemoveDependency,
-	CommandTest,
-	CommandTidy,
-	CommandUndeclaredName,
-	CommandUpdateGoSum,
-	CommandUpgradeDependency,
-	CommandVendor,
-}
-
-var (
-	// CommandTest runs `go test` for a specific test function.
-	CommandTest = &Command{
-		Name:  "test",
-		Title: "Run test(s)",
-		Async: true,
-	}
-
-	// CommandGenerate runs `go generate` for a given directory.
-	CommandGenerate = &Command{
-		Name:  "generate",
-		Title: "Run go generate",
-	}
-
-	// CommandTidy runs `go mod tidy` for a module.
-	CommandTidy = &Command{
-		Name:  "tidy",
-		Title: "Run go mod tidy",
-	}
-
-	// CommandVendor runs `go mod vendor` for a module.
-	CommandVendor = &Command{
-		Name:  "vendor",
-		Title: "Run go mod vendor",
-	}
-
-	// CommandGoGetPackage runs `go get` to fetch a package.
-	CommandGoGetPackage = &Command{
-		Name:  "go_get_package",
-		Title: "go get package",
-	}
-
-	// CommandUpdateGoSum updates the go.sum file for a module.
-	CommandUpdateGoSum = &Command{
-		Name:  "update_go_sum",
-		Title: "Update go.sum",
-	}
-
-	// CommandCheckUpgrades checks for module upgrades.
-	CommandCheckUpgrades = &Command{
-		Name:  "check_upgrades",
-		Title: "Check for upgrades",
-	}
-
-	// CommandAddDependency adds a dependency.
-	CommandAddDependency = &Command{
-		Name:  "add_dependency",
-		Title: "Add dependency",
-	}
-
-	// CommandUpgradeDependency upgrades a dependency.
-	CommandUpgradeDependency = &Command{
-		Name:  "upgrade_dependency",
-		Title: "Upgrade dependency",
-	}
-
-	// CommandRemoveDependency removes a dependency.
-	CommandRemoveDependency = &Command{
-		Name:  "remove_dependency",
-		Title: "Remove dependency",
-	}
-
-	// CommandRegenerateCgo regenerates cgo definitions.
-	CommandRegenerateCgo = &Command{
-		Name:  "regenerate_cgo",
-		Title: "Regenerate cgo",
-	}
-
-	// CommandToggleDetails controls calculation of gc annotations.
-	CommandToggleDetails = &Command{
-		Name:  "gc_details",
-		Title: "Toggle gc_details",
-	}
-
-	// CommandFillStruct is a gopls command to fill a struct with default
-	// values.
-	CommandFillStruct = &Command{
-		Name:  "fill_struct",
-		Title: "Fill struct",
-	}
-
-	// CommandUndeclaredName adds a variable declaration for an undeclared
-	// name.
-	CommandUndeclaredName = &Command{
-		Name:  "undeclared_name",
-		Title: "Undeclared name",
-	}
-
-	// CommandExtractVariable extracts an expression to a variable.
-	CommandExtractVariable = &Command{
-		Name:  "extract_variable",
-		Title: "Extract to variable",
-	}
-
-	// CommandExtractFunction extracts statements to a function.
-	CommandExtractFunction = &Command{
-		Name:  "extract_function",
-		Title: "Extract to function",
-	}
-
-	// CommandGenerateGoplsMod (re)generates the gopls.mod file.
-	CommandGenerateGoplsMod = &Command{
-		Name:  "generate_gopls_mod",
-		Title: "Generate gopls.mod",
-	}
-)
-
-// suggestedFixes maps a suggested fix command id to its handler.
-var suggestedFixes = map[string]SuggestedFixFunc{
-	CommandFillStruct.ID():      fillstruct.SuggestedFix,
-	CommandUndeclaredName.ID():  undeclaredname.SuggestedFix,
-	CommandExtractVariable.ID(): extractVariable,
-	CommandExtractFunction.ID(): extractFunction,
-}
-
-// ApplyFix applies the command's suggested fix to the given file and
-// range, returning the resulting edits.
-func ApplyFix(ctx context.Context, cmdid string, snapshot Snapshot, fh VersionedFileHandle, pRng protocol.Range) ([]protocol.TextDocumentEdit, error) {
-	handler, ok := suggestedFixes[cmdid]
-	if !ok {
-		return nil, fmt.Errorf("no suggested fix function for %s", cmdid)
-	}
-	fset, rng, src, file, m, pkg, info, err := getAllSuggestedFixInputs(ctx, snapshot, fh, pRng)
-	if err != nil {
-		return nil, err
-	}
-	fix, err := handler(fset, rng, src, file, pkg, info)
-	if err != nil {
-		return nil, err
-	}
-	if fix == nil {
-		return nil, nil
-	}
-
-	var edits []protocol.TextDocumentEdit
-	for _, edit := range fix.TextEdits {
-		rng := span.NewRange(fset, edit.Pos, edit.End)
-		spn, err := rng.Span()
-		if err != nil {
-			return nil, err
-		}
-		clRng, err := m.Range(spn)
-		if err != nil {
-			return nil, err
-		}
-		edits = append(edits, protocol.TextDocumentEdit{
-			TextDocument: protocol.OptionalVersionedTextDocumentIdentifier{
-				Version: fh.Version(),
-				TextDocumentIdentifier: protocol.TextDocumentIdentifier{
-					URI: protocol.URIFromSpanURI(fh.URI()),
-				},
-			},
-			Edits: []protocol.TextEdit{
-				{
-					Range:   clRng,
-					NewText: string(edit.NewText),
-				},
-			},
-		})
-	}
-	return edits, nil
-}
-
-// getAllSuggestedFixInputs is a helper function to collect all possible needed
-// inputs for an AppliesFunc or SuggestedFixFunc.
-func getAllSuggestedFixInputs(ctx context.Context, snapshot Snapshot, fh FileHandle, pRng protocol.Range) (*token.FileSet, span.Range, []byte, *ast.File, *protocol.ColumnMapper, *types.Package, *types.Info, error) {
-	pkg, pgf, err := GetParsedFile(ctx, snapshot, fh, NarrowestPackage)
-	if err != nil {
-		return nil, span.Range{}, nil, nil, nil, nil, nil, errors.Errorf("getting file for Identifier: %w", err)
-	}
-	rng, err := pgf.Mapper.RangeToSpanRange(pRng)
-	if err != nil {
-		return nil, span.Range{}, nil, nil, nil, nil, nil, err
-	}
-	return snapshot.FileSet(), rng, pgf.Src, pgf.File, pgf.Mapper, pkg.GetTypes(), pkg.GetTypesInfo(), nil
-}
diff --git a/internal/lsp/source/fix.go b/internal/lsp/source/fix.go
new file mode 100644
index 0000000..3918355
--- /dev/null
+++ b/internal/lsp/source/fix.go
@@ -0,0 +1,112 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package source
+
+import (
+	"context"
+	"fmt"
+	"go/ast"
+	"go/token"
+	"go/types"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/internal/lsp/analysis/fillstruct"
+	"golang.org/x/tools/internal/lsp/analysis/undeclaredname"
+	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/span"
+	errors "golang.org/x/xerrors"
+)
+
+// SuggestedFixFunc is a function used to get the suggested fixes for a given
+// gopls command, some of which are provided by go/analysis.Analyzers. Some of
+// the analyzers in internal/lsp/analysis are not efficient enough to include
+// suggested fixes with their diagnostics, so we have to compute them
+// separately. Such analyzers should provide a function with a signature of
+// SuggestedFixFunc.
+type SuggestedFixFunc func(fset *token.FileSet, rng span.Range, src []byte, file *ast.File, pkg *types.Package, info *types.Info) (*analysis.SuggestedFix, error)
+
+const (
+	FillStruct      = "fill_struct"
+	UndeclaredName  = "undeclared_name"
+	ExtractVariable = "extract_variable"
+	ExtractFunction = "extract_function"
+)
+
+// suggestedFixes maps a suggested fix command id to its handler.
+var suggestedFixes = map[string]SuggestedFixFunc{
+	FillStruct:      fillstruct.SuggestedFix,
+	UndeclaredName:  undeclaredname.SuggestedFix,
+	ExtractVariable: extractVariable,
+	ExtractFunction: extractFunction,
+}
+
+func SuggestedFixFromCommand(cmd protocol.Command) SuggestedFix {
+	return SuggestedFix{
+		Title:   cmd.Title,
+		Command: &cmd,
+	}
+}
+
+// ApplyFix applies the command's suggested fix to the given file and
+// range, returning the resulting edits.
+func ApplyFix(ctx context.Context, fix string, snapshot Snapshot, fh VersionedFileHandle, pRng protocol.Range) ([]protocol.TextDocumentEdit, error) {
+	handler, ok := suggestedFixes[fix]
+	if !ok {
+		return nil, fmt.Errorf("no suggested fix function for %s", fix)
+	}
+	fset, rng, src, file, m, pkg, info, err := getAllSuggestedFixInputs(ctx, snapshot, fh, pRng)
+	if err != nil {
+		return nil, err
+	}
+	suggestion, err := handler(fset, rng, src, file, pkg, info)
+	if err != nil {
+		return nil, err
+	}
+	if suggestion == nil {
+		return nil, nil
+	}
+
+	var edits []protocol.TextDocumentEdit
+	for _, edit := range suggestion.TextEdits {
+		rng := span.NewRange(fset, edit.Pos, edit.End)
+		spn, err := rng.Span()
+		if err != nil {
+			return nil, err
+		}
+		clRng, err := m.Range(spn)
+		if err != nil {
+			return nil, err
+		}
+		edits = append(edits, protocol.TextDocumentEdit{
+			TextDocument: protocol.OptionalVersionedTextDocumentIdentifier{
+				Version: fh.Version(),
+				TextDocumentIdentifier: protocol.TextDocumentIdentifier{
+					URI: protocol.URIFromSpanURI(fh.URI()),
+				},
+			},
+			Edits: []protocol.TextEdit{
+				{
+					Range:   clRng,
+					NewText: string(edit.NewText),
+				},
+			},
+		})
+	}
+	return edits, nil
+}
+
+// getAllSuggestedFixInputs is a helper function to collect all possible needed
+// inputs for an AppliesFunc or SuggestedFixFunc.
+func getAllSuggestedFixInputs(ctx context.Context, snapshot Snapshot, fh FileHandle, pRng protocol.Range) (*token.FileSet, span.Range, []byte, *ast.File, *protocol.ColumnMapper, *types.Package, *types.Info, error) {
+	pkg, pgf, err := GetParsedFile(ctx, snapshot, fh, NarrowestPackage)
+	if err != nil {
+		return nil, span.Range{}, nil, nil, nil, nil, nil, errors.Errorf("getting file for Identifier: %w", err)
+	}
+	rng, err := pgf.Mapper.RangeToSpanRange(pRng)
+	if err != nil {
+		return nil, span.Range{}, nil, nil, nil, nil, nil, err
+	}
+	return snapshot.FileSet(), rng, pgf.Src, pgf.File, pgf.Mapper, pkg.GetTypes(), pkg.GetTypesInfo(), nil
+}
diff --git a/internal/lsp/source/options.go b/internal/lsp/source/options.go
index 1584162..6758984 100644
--- a/internal/lsp/source/options.go
+++ b/internal/lsp/source/options.go
@@ -53,6 +53,7 @@
 	"golang.org/x/tools/internal/lsp/analysis/simplifyslice"
 	"golang.org/x/tools/internal/lsp/analysis/undeclaredname"
 	"golang.org/x/tools/internal/lsp/analysis/unusedparams"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/diff"
 	"golang.org/x/tools/internal/lsp/diff/myers"
 	"golang.org/x/tools/internal/lsp/protocol"
@@ -70,7 +71,7 @@
 func DefaultOptions() *Options {
 	optionsOnce.Do(func() {
 		var commands []string
-		for _, c := range Commands {
+		for _, c := range command.Commands {
 			commands = append(commands, c.ID())
 		}
 		defaultOptions = &Options{
@@ -129,12 +130,12 @@
 						CompletionBudget: 100 * time.Millisecond,
 					},
 					Codelenses: map[string]bool{
-						CommandGenerate.Name:          true,
-						CommandRegenerateCgo.Name:     true,
-						CommandTidy.Name:              true,
-						CommandToggleDetails.Name:     false,
-						CommandUpgradeDependency.Name: true,
-						CommandVendor.Name:            true,
+						string(command.Generate):          true,
+						string(command.RegenerateCgo):     true,
+						string(command.Tidy):              true,
+						string(command.GCDetails):         false,
+						string(command.UpgradeDependency): true,
+						string(command.Vendor):            true,
 					},
 				},
 			},
@@ -676,8 +677,8 @@
 }
 
 func (o *Options) enableAllExperimentMaps() {
-	if _, ok := o.Codelenses[CommandToggleDetails.Name]; !ok {
-		o.Codelenses[CommandToggleDetails.Name] = true
+	if _, ok := o.Codelenses[string(command.GCDetails)]; !ok {
+		o.Codelenses[string(command.GCDetails)] = true
 	}
 	if _, ok := o.Analyses[unusedparams.Analyzer.Name]; !ok {
 		o.Analyses[unusedparams.Analyzer.Name] = true
@@ -1089,7 +1090,7 @@
 		undeclaredname.Analyzer.Name: {
 			Analyzer:   undeclaredname.Analyzer,
 			FixesError: undeclaredname.FixesError,
-			Command:    CommandUndeclaredName,
+			Fix:        UndeclaredName,
 			Enabled:    true,
 		},
 	}
@@ -1099,7 +1100,7 @@
 	return map[string]Analyzer{
 		fillstruct.Analyzer.Name: {
 			Analyzer: fillstruct.Analyzer,
-			Command:  CommandFillStruct,
+			Fix:      FillStruct,
 			Enabled:  true,
 		},
 	}
diff --git a/internal/lsp/source/util.go b/internal/lsp/source/util.go
index e559e5c..c1ba082 100644
--- a/internal/lsp/source/util.go
+++ b/internal/lsp/source/util.go
@@ -6,8 +6,6 @@
 
 import (
 	"context"
-	"encoding/json"
-	"fmt"
 	"go/ast"
 	"go/printer"
 	"go/token"
@@ -293,50 +291,6 @@
 	return nil, nil, errors.Errorf("no file for %s in package %s", uri, pkg.ID())
 }
 
-// MarshalArgs encodes the given arguments to json.RawMessages. This function
-// is used to construct arguments to a protocol.Command.
-//
-// Example usage:
-//
-//   jsonArgs, err := EncodeArgs(1, "hello", true, StructuredArg{42, 12.6})
-//
-func MarshalArgs(args ...interface{}) ([]json.RawMessage, error) {
-	var out []json.RawMessage
-	for _, arg := range args {
-		argJSON, err := json.Marshal(arg)
-		if err != nil {
-			return nil, err
-		}
-		out = append(out, argJSON)
-	}
-	return out, nil
-}
-
-// UnmarshalArgs decodes the given json.RawMessages to the variables provided
-// by args. Each element of args should be a pointer.
-//
-// Example usage:
-//
-//   var (
-//       num int
-//       str string
-//       bul bool
-//       structured StructuredArg
-//   )
-//   err := UnmarshalArgs(args, &num, &str, &bul, &structured)
-//
-func UnmarshalArgs(jsonArgs []json.RawMessage, args ...interface{}) error {
-	if len(args) != len(jsonArgs) {
-		return fmt.Errorf("DecodeArgs: expected %d input arguments, got %d JSON arguments", len(args), len(jsonArgs))
-	}
-	for i, arg := range args {
-		if err := json.Unmarshal(jsonArgs[i], arg); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
 // ImportPath returns the unquoted import path of s,
 // or "" if the path is not properly quoted.
 func ImportPath(s *ast.ImportSpec) string {
diff --git a/internal/lsp/source/view.go b/internal/lsp/source/view.go
index 90b25e1..964d631 100644
--- a/internal/lsp/source/view.go
+++ b/internal/lsp/source/view.go
@@ -505,11 +505,11 @@
 	// the value of the Staticcheck setting overrides this field.
 	Enabled bool
 
-	// Command is the name of the command used to invoke the suggested fixes
-	// for the analyzer. It is non-nil if we expect this analyzer to provide
-	// its fix separately from its diagnostics. That is, we should apply the
-	// analyzer's suggested fixes through a Command, not a TextEdit.
-	Command *Command
+	// Fix is the name of the suggested fix name used to invoke the suggested
+	// fixes for the analyzer. It is non-empty if we expect this analyzer to
+	// provide its fix separately from its diagnostics. That is, we should apply
+	// the analyzer's suggested fixes through a Command, not a TextEdit.
+	Fix string
 
 	// If this is true, then we can apply the suggested fixes
 	// as part of a source.FixAll codeaction.
diff --git a/internal/lsp/tests/tests.go b/internal/lsp/tests/tests.go
index c99086a..e46c199 100644
--- a/internal/lsp/tests/tests.go
+++ b/internal/lsp/tests/tests.go
@@ -26,6 +26,7 @@
 	"golang.org/x/tools/go/expect"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/go/packages/packagestest"
+	"golang.org/x/tools/internal/lsp/command"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/lsp/source/completion"
@@ -234,7 +235,7 @@
 		},
 		source.Sum: {},
 	}
-	o.UserOptions.Codelenses[source.CommandTest.Name] = true
+	o.UserOptions.Codelenses[string(command.Test)] = true
 	o.HoverKind = source.SynopsisDocumentation
 	o.InsertTextFormat = protocol.SnippetTextFormat
 	o.CompletionBudget = time.Minute