diff --git a/internal/lsp/cache/load.go b/internal/lsp/cache/load.go
index 12a09b6..0d07070 100644
--- a/internal/lsp/cache/load.go
+++ b/internal/lsp/cache/load.go
@@ -16,6 +16,7 @@
 
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/event"
+	"golang.org/x/tools/internal/gocommand"
 	"golang.org/x/tools/internal/lsp/debug/tag"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/packagesinternal"
@@ -91,70 +92,14 @@
 	defer done()
 
 	cleanup := func() {}
-	wdir := s.view.rootURI.Filename()
 
-	var modFile string
-	var modURI span.URI
-	var modContent []byte
-	switch {
-	case s.workspaceMode()&usesWorkspaceModule != 0:
-		var (
-			tmpDir span.URI
-			err    error
-		)
-		tmpDir, cleanup, err = s.tempWorkspaceModule(ctx)
-		if err != nil {
-			return err
-		}
-		wdir = tmpDir.Filename()
-		modURI = span.URIFromPath(filepath.Join(wdir, "go.mod"))
-		modContent, err = ioutil.ReadFile(modURI.Filename())
-		if err != nil {
-			return err
-		}
-	case s.workspaceMode()&tempModfile != 0:
-		// -modfile is unsupported when there are > 1 modules in the workspace.
-		if len(s.modules) != 1 {
-			panic(fmt.Sprintf("unsupported use of -modfile, expected 1 module, got %v", len(s.modules)))
-		}
-		var mod *moduleRoot
-		for _, m := range s.modules { // range to access the only element
-			mod = m
-		}
-		modURI = mod.modURI
-		modFH, err := s.GetFile(ctx, mod.modURI)
-		if err != nil {
-			return err
-		}
-		modContent, err = modFH.Read()
-		if err != nil {
-			return err
-		}
-		var sumFH source.FileHandle
-		if mod.sumURI != "" {
-			sumFH, err = s.GetFile(ctx, mod.sumURI)
-			if err != nil {
-				return err
-			}
-		}
-		var tmpURI span.URI
-		tmpURI, cleanup, err = tempModFile(modFH, sumFH)
-		if err != nil {
-			return err
-		}
-		modFile = tmpURI.Filename()
-	}
-
-	cfg := s.config(ctx, wdir)
-	packagesinternal.SetModFile(cfg, modFile)
-	modMod, err := s.needsModEqualsMod(ctx, modURI, modContent)
+	_, inv, cleanup, err := s.goCommandInvocation(ctx, source.ForTypeChecking, &gocommand.Invocation{
+		WorkingDir: s.view.rootURI.Filename(),
+	})
 	if err != nil {
 		return err
 	}
-	if modMod {
-		packagesinternal.SetModFlag(cfg, "mod")
-	}
-
+	cfg := s.config(ctx, inv)
 	pkgs, err := packages.Load(cfg, query...)
 	cleanup()
 
diff --git a/internal/lsp/cache/mod.go b/internal/lsp/cache/mod.go
index 736b56b..f95590f 100644
--- a/internal/lsp/cache/mod.go
+++ b/internal/lsp/cache/mod.go
@@ -238,7 +238,7 @@
 		for _, req := range pm.File.Require {
 			inv.Args = append(inv.Args, req.Mod.Path)
 		}
-		stdout, err := snapshot.RunGoCommandDirect(ctx, inv)
+		stdout, err := snapshot.RunGoCommandDirect(ctx, source.Normal, inv)
 		if err != nil {
 			return &modWhyData{err: err}
 		}
@@ -336,7 +336,7 @@
 			// (see golang/go#38711).
 			inv.ModFlag = "readonly"
 		}
-		stdout, err := snapshot.RunGoCommandDirect(ctx, inv)
+		stdout, err := snapshot.RunGoCommandDirect(ctx, source.Normal, inv)
 		if err != nil {
 			return &modUpgradeData{err: err}
 		}
diff --git a/internal/lsp/cache/mod_tidy.go b/internal/lsp/cache/mod_tidy.go
index 375fddc..9e92287 100644
--- a/internal/lsp/cache/mod_tidy.go
+++ b/internal/lsp/cache/mod_tidy.go
@@ -57,9 +57,6 @@
 	if fh.Kind() != source.Mod {
 		return nil, fmt.Errorf("%s is not a go.mod file", fh.URI())
 	}
-	if s.workspaceMode()&tempModfile == 0 {
-		return nil, source.ErrTmpModfileUnsupported
-	}
 	if handle := s.getModTidyHandle(fh.URI()); handle != nil {
 		return handle.tidy(ctx, s)
 	}
@@ -118,7 +115,7 @@
 			Args:       []string{"tidy"},
 			WorkingDir: filepath.Dir(fh.URI().Filename()),
 		}
-		tmpURI, inv, cleanup, err := snapshot.goCommandInvocation(ctx, true, inv)
+		tmpURI, inv, cleanup, err := snapshot.goCommandInvocation(ctx, source.WriteTemporaryModFile, inv)
 		if err != nil {
 			return &modTidyData{err: err}
 		}
diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index 34d78a1..27b8ba1 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -182,18 +182,16 @@
 // TODO(rstambler): go/packages requires that we do not provide overlays for
 // multiple modules in on config, so buildOverlay needs to filter overlays by
 // module.
-func (s *snapshot) config(ctx context.Context, dir string) *packages.Config {
+func (s *snapshot) config(ctx context.Context, inv *gocommand.Invocation) *packages.Config {
 	s.view.optionsMu.Lock()
-	env := s.view.options.EnvSlice()
-	buildFlags := append([]string{}, s.view.options.BuildFlags...)
 	verboseOutput := s.view.options.VerboseOutput
 	s.view.optionsMu.Unlock()
 
 	cfg := &packages.Config{
 		Context:    ctx,
-		Dir:        dir,
-		Env:        append(append([]string{}, env...), "GO111MODULE="+s.view.go111module),
-		BuildFlags: buildFlags,
+		Dir:        inv.WorkingDir,
+		Env:        inv.Env,
+		BuildFlags: inv.BuildFlags,
 		Mode: packages.NeedName |
 			packages.NeedFiles |
 			packages.NeedCompiledGoFiles |
@@ -213,6 +211,8 @@
 		},
 		Tests: true,
 	}
+	packagesinternal.SetModFile(cfg, inv.ModFile)
+	packagesinternal.SetModFlag(cfg, inv.ModFlag)
 	// We want to type check cgo code if go/types supports it.
 	if typesinternal.SetUsesCgo(&types.Config{}) {
 		cfg.Mode |= packages.LoadMode(packagesinternal.TypecheckCgo)
@@ -221,8 +221,8 @@
 	return cfg
 }
 
-func (s *snapshot) RunGoCommandDirect(ctx context.Context, inv *gocommand.Invocation) (*bytes.Buffer, error) {
-	_, inv, cleanup, err := s.goCommandInvocation(ctx, false, inv)
+func (s *snapshot) RunGoCommandDirect(ctx context.Context, mode source.InvocationMode, inv *gocommand.Invocation) (*bytes.Buffer, error) {
+	_, inv, cleanup, err := s.goCommandInvocation(ctx, mode, inv)
 	if err != nil {
 		return nil, err
 	}
@@ -231,8 +231,8 @@
 	return s.view.session.gocmdRunner.Run(ctx, *inv)
 }
 
-func (s *snapshot) RunGoCommandPiped(ctx context.Context, inv *gocommand.Invocation, stdout, stderr io.Writer) error {
-	_, inv, cleanup, err := s.goCommandInvocation(ctx, true, inv)
+func (s *snapshot) RunGoCommandPiped(ctx context.Context, mode source.InvocationMode, inv *gocommand.Invocation, stdout, stderr io.Writer) error {
+	_, inv, cleanup, err := s.goCommandInvocation(ctx, mode, inv)
 	if err != nil {
 		return err
 	}
@@ -240,16 +240,49 @@
 	return s.view.session.gocmdRunner.RunPiped(ctx, *inv, stdout, stderr)
 }
 
-func (s *snapshot) goCommandInvocation(ctx context.Context, allowTempModfile bool, inv *gocommand.Invocation) (tmpURI span.URI, updatedInv *gocommand.Invocation, cleanup func(), err error) {
+func (s *snapshot) goCommandInvocation(ctx context.Context, mode source.InvocationMode, inv *gocommand.Invocation) (tmpURI span.URI, updatedInv *gocommand.Invocation, cleanup func(), err error) {
 	s.view.optionsMu.Lock()
-	env := s.view.options.EnvSlice()
+	inv.Env = append(append(append([]string{}, s.view.options.EnvSlice()...), inv.Env...), "GO111MODULE="+s.view.go111module)
+	inv.BuildFlags = append([]string{}, s.view.options.BuildFlags...)
 	s.view.optionsMu.Unlock()
-
 	cleanup = func() {} // fallback
-	inv.Env = append(append(append([]string{}, env...), inv.Env...), "GO111MODULE="+s.view.go111module)
 
-	modURI := s.GoModForFile(ctx, span.URIFromPath(inv.WorkingDir))
-	if allowTempModfile && s.workspaceMode()&tempModfile != 0 {
+	var modURI span.URI
+	if s.workspaceMode()&moduleMode != 0 {
+		// Select the module context to use.
+		// If we're type checking, we need to use the workspace context, meaning
+		// the main (workspace) module. Otherwise, we should use the module for
+		// the passed-in working dir.
+		if mode == source.ForTypeChecking {
+			if s.workspaceMode()&usesWorkspaceModule == 0 {
+				var mod *moduleRoot
+				for _, m := range s.modules { // range to access the only element
+					mod = m
+				}
+				modURI = mod.modURI
+			} else {
+				var tmpDir span.URI
+				var err error
+				tmpDir, cleanup, err = s.tempWorkspaceModule(ctx)
+				if err != nil {
+					return "", nil, cleanup, err
+				}
+				inv.WorkingDir = tmpDir.Filename()
+				modURI = span.URIFromPath(filepath.Join(tmpDir.Filename(), "go.mod"))
+			}
+		} else {
+			modURI = s.GoModForFile(ctx, span.URIFromPath(inv.WorkingDir))
+		}
+	}
+
+	wantTempMod := mode != source.UpdateUserModFile
+	needTempMod := mode == source.WriteTemporaryModFile
+	tempMod := wantTempMod && s.workspaceMode()&tempModfile != 0
+	if needTempMod && !tempMod {
+		return "", nil, cleanup, source.ErrTmpModfileUnsupported
+	}
+
+	if tempMod {
 		if modURI == "" {
 			return "", nil, cleanup, fmt.Errorf("no go.mod file found in %s", inv.WorkingDir)
 		}
diff --git a/internal/lsp/command.go b/internal/lsp/command.go
index 80e762c..134d3fd 100644
--- a/internal/lsp/command.go
+++ b/internal/lsp/command.go
@@ -265,7 +265,7 @@
 	}
 	snapshot, release := view.Snapshot(ctx)
 	defer release()
-	_, err = snapshot.RunGoCommandDirect(ctx, &gocommand.Invocation{
+	_, err = snapshot.RunGoCommandDirect(ctx, source.UpdateUserModFile, &gocommand.Invocation{
 		Verb:       verb,
 		Args:       args,
 		WorkingDir: filepath.Dir(uri.SpanURI().Filename()),
@@ -296,7 +296,7 @@
 			Args:       []string{pkgPath, "-v", "-count=1", "-run", fmt.Sprintf("^%s$", funcName)},
 			WorkingDir: filepath.Dir(uri.SpanURI().Filename()),
 		}
-		if err := snapshot.RunGoCommandPiped(ctx, inv, out, out); err != nil {
+		if err := snapshot.RunGoCommandPiped(ctx, source.Normal, inv, out, out); err != nil {
 			if errors.Is(err, context.Canceled) {
 				return err
 			}
@@ -312,7 +312,7 @@
 			Args:       []string{pkgPath, "-v", "-run=^$", "-bench", fmt.Sprintf("^%s$", funcName)},
 			WorkingDir: filepath.Dir(uri.SpanURI().Filename()),
 		}
-		if err := snapshot.RunGoCommandPiped(ctx, inv, out, out); err != nil {
+		if err := snapshot.RunGoCommandPiped(ctx, source.Normal, inv, out, out); err != nil {
 			if errors.Is(err, context.Canceled) {
 				return err
 			}
@@ -367,7 +367,7 @@
 		WorkingDir: dir.Filename(),
 	}
 	stderr := io.MultiWriter(er, workDoneWriter{work})
-	if err := snapshot.RunGoCommandPiped(ctx, inv, er, stderr); err != nil {
+	if err := snapshot.RunGoCommandPiped(ctx, source.Normal, inv, er, stderr); err != nil {
 		return err
 	}
 	return nil
diff --git a/internal/lsp/source/gc_annotations.go b/internal/lsp/source/gc_annotations.go
index 0a0d2b5..8bf8ad7 100644
--- a/internal/lsp/source/gc_annotations.go
+++ b/internal/lsp/source/gc_annotations.go
@@ -46,7 +46,7 @@
 		},
 		WorkingDir: pkgDir.Filename(),
 	}
-	_, err = snapshot.RunGoCommandDirect(ctx, inv)
+	_, err = snapshot.RunGoCommandDirect(ctx, Normal, inv)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/lsp/source/view.go b/internal/lsp/source/view.go
index 2f3a212..8a12e0c 100644
--- a/internal/lsp/source/view.go
+++ b/internal/lsp/source/view.go
@@ -84,11 +84,11 @@
 
 	// RunGoCommandPiped runs the given `go` command, writing its output
 	// to stdout and stderr. Verb, Args, and WorkingDir must be specified.
-	RunGoCommandPiped(ctx context.Context, inv *gocommand.Invocation, stdout, stderr io.Writer) error
+	RunGoCommandPiped(ctx context.Context, mode InvocationMode, inv *gocommand.Invocation, stdout, stderr io.Writer) error
 
 	// RunGoCommandDirect runs the given `go` command. Verb, Args, and
 	// WorkingDir must be specified.
-	RunGoCommandDirect(ctx context.Context, inv *gocommand.Invocation) (*bytes.Buffer, error)
+	RunGoCommandDirect(ctx context.Context, mode InvocationMode, inv *gocommand.Invocation) (*bytes.Buffer, error)
 
 	// RunProcessEnvFunc runs fn with the process env for this snapshot's view.
 	// Note: the process env contains cached module and filesystem state.
@@ -169,6 +169,24 @@
 	WidestPackage
 )
 
+// InvocationMode represents the goal of a particular go command invocation.
+type InvocationMode int
+
+const (
+	// Normal is appropriate for commands that might be run by a user and don't
+	// deliberately modify go.mod files, e.g. `go test`.
+	Normal = iota
+	// UpdateUserModFile is for commands that intend to update the user's real
+	// go.mod file, e.g. `go mod tidy` in response to a user's request to tidy.
+	UpdateUserModFile
+	// WriteTemporaryModFile is for commands that need information from a
+	// modified version of the user's go.mod file, e.g. `go mod tidy` used to
+	// generate diagnostics.
+	WriteTemporaryModFile
+	// ForTypeChecking is for packages.Load.
+	ForTypeChecking
+)
+
 // View represents a single workspace.
 // This is the level at which we maintain configuration like working directory
 // and build tags.