// Copyright 2023 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 regtest

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"go/token"
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"reflect"
	"regexp"
	"sort"
	"strings"
	"testing"

	"github.com/google/go-cmp/cmp"
	"golang.org/x/tools/go/expect"
	"golang.org/x/tools/gopls/internal/hooks"
	"golang.org/x/tools/gopls/internal/lsp/cache"
	"golang.org/x/tools/gopls/internal/lsp/debug"
	"golang.org/x/tools/gopls/internal/lsp/fake"
	"golang.org/x/tools/gopls/internal/lsp/lsprpc"
	"golang.org/x/tools/gopls/internal/lsp/protocol"
	"golang.org/x/tools/gopls/internal/lsp/safetoken"
	"golang.org/x/tools/gopls/internal/lsp/source"
	"golang.org/x/tools/gopls/internal/lsp/tests"
	"golang.org/x/tools/gopls/internal/lsp/tests/compare"
	"golang.org/x/tools/internal/diff"
	"golang.org/x/tools/internal/jsonrpc2"
	"golang.org/x/tools/internal/jsonrpc2/servertest"
	"golang.org/x/tools/internal/testenv"
	"golang.org/x/tools/txtar"
)

var update = flag.Bool("update", false, "if set, update test data during marker tests")

// RunMarkerTests runs "marker" tests in the given test data directory.
// (In practice: ../../regtest/marker/testdata)
//
// A marker test uses the '//@' marker syntax of the x/tools/go/expect package
// to annotate source code with various information such as locations and
// arguments of LSP operations to be executed by the test. The syntax following
// '@' is parsed as a comma-separated list of ordinary Go function calls, for
// example
//
//	//@foo(a, "b", 3),bar(0)
//
// and delegates to a corresponding function to perform LSP-related operations.
// See the Marker types documentation below for a list of supported markers.
//
// Each call argument is converted to the type of the corresponding parameter of
// the designated function. The conversion logic may use the surrounding context,
// such as the position or nearby text. See the Argument conversion section below
// for the full set of special conversions. As a special case, the blank
// identifier '_' is treated as the zero value of the parameter type.
//
// The test runner collects test cases by searching the given directory for
// files with the .txt extension. Each file is interpreted as a txtar archive,
// which is extracted to a temporary directory. The relative path to the .txt
// file is used as the subtest name. The preliminary section of the file
// (before the first archive entry) is a free-form comment.
//
// These tests were inspired by (and in many places copied from) a previous
// iteration of the marker tests built on top of the packagestest framework.
// Key design decisions motivating this reimplementation are as follows:
//   - The old tests had a single global session, causing interaction at a
//     distance and several awkward workarounds.
//   - The old tests could not be safely parallelized, because certain tests
//     manipulated the server options
//   - Relatedly, the old tests did not have a logic grouping of assertions into
//     a single unit, resulting in clusters of files serving clusters of
//     entangled assertions.
//   - The old tests used locations in the source as test names and as the
//     identity of golden content, meaning that a single edit could change the
//     name of an arbitrary number of subtests, and making it difficult to
//     manually edit golden content.
//   - The old tests did not hew closely to LSP concepts, resulting in, for
//     example, each marker implementation doing its own position
//     transformations, and inventing its own mechanism for configuration.
//   - The old tests had an ad-hoc session initialization process. The regtest
//     environment has had more time devoted to its initialization, and has a
//     more convenient API.
//   - The old tests lacked documentation, and often had failures that were hard
//     to understand. By starting from scratch, we can revisit these aspects.
//
// # Special files
//
// There are three types of file within the test archive that are given special
// treatment by the test runner:
//   - "flags": this file is treated as a whitespace-separated list of flags
//     that configure the MarkerTest instance. For example, -min_go=go1.18 sets
//     the minimum required Go version for the test.
//     TODO(rfindley): support flag values containing whitespace.
//   - "settings.json": this file is parsed as JSON, and used as the
//     session configuration (see gopls/doc/settings.md)
//   - "env": this file is parsed as a list of VAR=VALUE fields specifying the
//     editor environment.
//   - Golden files: Within the archive, file names starting with '@' are
//     treated as "golden" content, and are not written to disk, but instead are
//     made available to test methods expecting an argument of type *Golden,
//     using the identifier following '@'. For example, if the first parameter of
//     Foo were of type *Golden, the test runner would convert the identifier a
//     in the call @foo(a, "b", 3) into a *Golden by collecting golden file
//     data starting with "@a/".
//
// # Marker types
//
// The following markers are supported within marker tests:
//
//   - complete(location, ...labels): specifies expected completion results at
//     the given location.
//
//   - diag(location, regexp): specifies an expected diagnostic matching the
//     given regexp at the given location. The test runner requires
//     a 1:1 correspondence between observed diagnostics and diag annotations
//
//   - def(src, dst location): perform a textDocument/definition request at
//     the src location, and check the the result points to the dst location.
//
//   - hover(src, dst location, g Golden): perform a textDocument/hover at the
//     src location, and checks that the result is the dst location, with hover
//     content matching "hover.md" in the golden data g.
//
//   - loc(name, location): specifies the name for a location in the source. These
//     locations may be referenced by other markers.
//
//   - rename(location, new, golden): specifies a renaming of the
//     identifier at the specified location to the new name.
//     The golden directory contains the transformed files.
//
//   - renameerr(location, new, wantError): specifies a renaming that
//     fails with an error that matches the expectation.
//
//   - suggestedfix(location, regexp, kind, golden): like diag, the location and
//     regexp identify an expected diagnostic. This diagnostic must
//     to have exactly one associated code action of the specified kind.
//     This action is executed for its editing effects on the source files.
//     Like rename, the golden directory contains the expected transformed files.
//
//   - refs(location, want ...location): executes a 'references' query at the
//     first location and asserts that the result is the set of 'want' locations.
//     The first want location must be the declaration (assumedly unique).
//
// # Argument conversion
//
// Marker arguments are first parsed by the go/expect package, which accepts
// the following tokens as defined by the Go spec:
//   - string, int64, float64, and rune literals
//   - true and false
//   - nil
//   - identifiers (type expect.Identifier)
//   - regular expressions, denoted the two tokens re"abc" (type *regexp.Regexp)
//
// These values are passed as arguments to the corresponding parameter of the
// test function. Additional value conversions may occur for these argument ->
// parameter type pairs:
//   - string->regexp: the argument is parsed as a regular expressions.
//   - string->location: the argument is converted to the location of the first
//     instance of the argument in the partial line preceding the note.
//   - regexp->location: the argument is converted to the location of the first
//     match for the argument in the partial line preceding the note. If the
//     regular expression contains exactly one subgroup, the position of the
//     subgroup is used rather than the position of the submatch.
//   - name->location: the argument is replaced by the named location.
//   - name->Golden: the argument is used to look up golden content prefixed by
//     @<argument>.
//   - {string,regexp,identifier}->wantError: a wantError type specifies
//     an expected error message, either in the form of a substring that
//     must be present, a regular expression that it must match, or an
//     identifier (e.g. foo) such that the archive entry @foo
//     exists and contains the exact expected error.
//
// # Example
//
// Here is a complete example:
//
//	-- a.go --
//	package a
//
//	const abc = 0x2a //@hover("b", "abc", abc),hover(" =", "abc", abc)
//	-- @abc/hover.md --
//	```go
//	const abc untyped int = 42
//	```
//
//	@hover("b", "abc", abc),hover(" =", "abc", abc)
//
// In this example, the @hover annotation tells the test runner to run the
// hoverMarker function, which has parameters:
//
//	(mark marker, src, dsc protocol.Location, g *Golden).
//
// The first argument holds the test context, including fake editor with open
// files, and sandboxed directory.
//
// Argument converters translate the "b" and "abc" arguments into locations by
// interpreting each one as a regular expression and finding the location of
// its first match on the preceding portion of the line, and the abc identifier
// into a dictionary of golden content containing "hover.md". Then the
// hoverMarker method executes a textDocument/hover LSP request at the src
// position, and ensures the result spans "abc", with the markdown content from
// hover.md. (Note that the markdown content includes the expect annotation as
// the doc comment.)
//
// The next hover on the same line asserts the same result, but initiates the
// hover immediately after "abc" in the source. This tests that we find the
// preceding identifier when hovering.
//
// # Updating golden files
//
// To update golden content in the test archive, it is easier to regenerate
// content automatically rather than edit it by hand. To do this, run the
// tests with the -update flag. Only tests that actually run will be updated.
//
// In some cases, golden content will vary by Go version (for example, gopls
// produces different markdown at Go versions before the 1.19 go/doc update).
// By convention, the golden content in test archives should match the output
// at Go tip. Each test function can normalize golden content for older Go
// versions.
//
// Note that -update does not cause missing @diag or @loc markers to be added.
//
// # TODO
//
// This API is a work-in-progress, as we migrate existing marker tests from
// internal/lsp/tests.
//
// Remaining TODO:
//   - parallelize/optimize test execution
//   - reorganize regtest packages (and rename to just 'test'?)
//   - Rename the files .txtar.
//
// Existing marker tests to port:
//   - CallHierarchy
//   - CodeLens
//   - Diagnostics
//   - CompletionItems
//   - Completions
//   - CompletionSnippets
//   - UnimportedCompletions
//   - DeepCompletions
//   - FuzzyCompletions
//   - CaseSensitiveCompletions
//   - RankCompletions
//   - FoldingRanges
//   - Formats
//   - Imports
//   - SemanticTokens
//   - FunctionExtractions
//   - MethodExtractions
//   - Definitions
//   - Implementations
//   - Highlights
//   - Renames
//   - PrepareRenames
//   - Symbols
//   - InlayHints
//   - WorkspaceSymbols
//   - Signatures
//   - Links
//   - AddImport
//   - SelectionRanges
func RunMarkerTests(t *testing.T, dir string) {
	// The marker tests must be able to run go/packages.Load.
	testenv.NeedsGoPackages(t)

	tests, err := loadMarkerTests(dir)
	if err != nil {
		t.Fatal(err)
	}

	// Opt: use a shared cache.
	// TODO(rfindley): opt: use a memoize store with no eviction.
	cache := cache.New(nil)

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			// TODO(rfindley): it may be more useful to have full support for build
			// constraints.
			if test.minGoVersion != "" {
				var go1point int
				if _, err := fmt.Sscanf(test.minGoVersion, "go1.%d", &go1point); err != nil {
					t.Fatalf("parsing -min_go version: %v", err)
				}
				testenv.NeedsGo1Point(t, 18)
			}
			config := fake.EditorConfig{
				Settings: test.settings,
				Env:      test.env,
			}
			if _, ok := config.Settings["diagnosticsDelay"]; !ok {
				if config.Settings == nil {
					config.Settings = make(map[string]interface{})
				}
				config.Settings["diagnosticsDelay"] = "10ms"
			}
			run := &markerTestRun{
				test: test,
				env:  newEnv(t, cache, test.files, config),

				locations: make(map[expect.Identifier]protocol.Location),
				diags:     make(map[protocol.Location][]protocol.Diagnostic),
			}
			// TODO(rfindley): make it easier to clean up the regtest environment.
			defer run.env.Editor.Shutdown(context.Background()) // ignore error
			defer run.env.Sandbox.Close()                       // ignore error

			// Open all files so that we operate consistently with LSP clients, and
			// (pragmatically) so that we have a Mapper available via the fake
			// editor.
			//
			// This also allows avoiding mutating the editor state in tests.
			for file := range test.files {
				run.env.OpenFile(file)
			}

			// Pre-process locations.
			var markers []marker
			for _, note := range test.notes {
				mark := marker{run: run, note: note}
				switch note.Name {
				case "loc":
					mark.execute()
				default:
					markers = append(markers, mark)
				}
			}

			// Wait for the didOpen notifications to be processed, then collect
			// diagnostics.
			var diags map[string]*protocol.PublishDiagnosticsParams
			run.env.AfterChange(ReadAllDiagnostics(&diags))
			for path, params := range diags {
				uri := run.env.Sandbox.Workdir.URI(path)
				for _, diag := range params.Diagnostics {
					loc := protocol.Location{
						URI:   uri,
						Range: diag.Range,
					}
					run.diags[loc] = append(run.diags[loc], diag)
				}
			}

			// Invoke each remaining marker in the test.
			for _, mark := range markers {
				mark.execute()
			}

			// Any remaining (un-eliminated) diagnostics are an error.
			for loc, diags := range run.diags {
				for _, diag := range diags {
					t.Errorf("%s: unexpected diagnostic: %q", run.fmtLoc(loc), diag.Message)
				}
			}

			formatted, err := formatTest(test)
			if err != nil {
				t.Errorf("formatTest: %v", err)
			} else if *update {
				filename := filepath.Join(dir, test.name)
				if err := os.WriteFile(filename, formatted, 0644); err != nil {
					t.Error(err)
				}
			} else {
				// On go 1.19 and later, verify that the testdata has not changed.
				//
				// On earlier Go versions, the golden test data varies due to different
				// markdown escaping.
				//
				// Only check this if the test hasn't already failed, otherwise we'd
				// report duplicate mismatches of golden data.
				if testenv.Go1Point() >= 19 && !t.Failed() {
					// Otherwise, verify that formatted content matches.
					if diff := compare.NamedText("formatted", "on-disk", string(formatted), string(test.content)); diff != "" {
						t.Errorf("formatted test does not match on-disk content:\n%s", diff)
					}
				}
			}
		})
	}

	if abs, err := filepath.Abs(dir); err == nil && t.Failed() {
		t.Logf("(Filenames are relative to %s.)", abs)
	}
}

// A marker holds state for the execution of a single @marker
// annotation in the source.
type marker struct {
	run  *markerTestRun
	note *expect.Note
}

// errorf reports an error with a prefix indicating the position of the marker note.
//
// It formats the error message using mark.sprintf.
func (mark marker) errorf(format string, args ...interface{}) {
	msg := mark.sprintf(format, args...)
	// TODO(adonovan): consider using fmt.Fprintf(os.Stderr)+t.Fail instead of
	// t.Errorf to avoid reporting uninteresting positions in the Go source of
	// the driver. However, this loses the order of stderr wrt "FAIL: TestFoo"
	// subtest dividers.
	mark.run.env.T.Errorf("%s: %s", mark.run.fmtPos(mark.note.Pos), msg)
}

// execute invokes the marker's function with the arguments from note.
func (mark marker) execute() {
	fn, ok := markerFuncs[mark.note.Name]
	if !ok {
		mark.errorf("no marker function named %s", mark.note.Name)
		return
	}

	// The first converter corresponds to the *Env argument.
	// All others must be converted from the marker syntax.
	args := []reflect.Value{reflect.ValueOf(mark)}
	var convert converter
	for i, in := range mark.note.Args {
		if i < len(fn.converters) {
			convert = fn.converters[i]
		} else if !fn.variadic {
			mark.errorf("got %d arguments to %s, expect %d",
				len(mark.note.Args), mark.note.Name, len(fn.converters))
			return
		}

		// Special handling for the blank identifier: treat it as the zero value.
		if ident, ok := in.(expect.Identifier); ok && ident == "_" {
			zero := reflect.Zero(fn.paramTypes[i])
			args = append(args, zero)
			continue
		}

		out, err := convert(mark, in)
		if err != nil {
			mark.errorf("converting argument #%d of %s (%v): %v", i, mark.note.Name, in, err)
			return
		}
		args = append(args, reflect.ValueOf(out))
	}

	fn.fn.Call(args)
}

// Supported marker functions.
//
// Each marker function must accept a marker as its first argument, with
// subsequent arguments converted from the marker arguments.
//
// Marker funcs should not mutate the test environment (e.g. via opening files
// or applying edits in the editor).
var markerFuncs = map[string]markerFunc{
	"complete":     makeMarkerFunc(completeMarker),
	"def":          makeMarkerFunc(defMarker),
	"diag":         makeMarkerFunc(diagMarker),
	"hover":        makeMarkerFunc(hoverMarker),
	"loc":          makeMarkerFunc(locMarker),
	"rename":       makeMarkerFunc(renameMarker),
	"renameerr":    makeMarkerFunc(renameErrMarker),
	"suggestedfix": makeMarkerFunc(suggestedfixMarker),
	"refs":         makeMarkerFunc(refsMarker),
}

// markerTest holds all the test data extracted from a test txtar archive.
//
// See the documentation for RunMarkerTests for more information on the archive
// format.
type markerTest struct {
	name     string                 // relative path to the txtar file in the testdata dir
	fset     *token.FileSet         // fileset used for parsing notes
	content  []byte                 // raw test content
	archive  *txtar.Archive         // original test archive
	settings map[string]interface{} // gopls settings
	env      map[string]string      // editor environment
	files    map[string][]byte      // data files from the archive (excluding special files)
	notes    []*expect.Note         // extracted notes from data files
	golden   map[string]*Golden     // extracted golden content, by identifier name

	// flags holds flags extracted from the special "flags" archive file.
	flags []string
	// Parsed flags values.
	minGoVersion string
}

// flagSet returns the flagset used for parsing the special "flags" file in the
// test archive.
func (t *markerTest) flagSet() *flag.FlagSet {
	flags := flag.NewFlagSet(t.name, flag.ContinueOnError)
	flags.StringVar(&t.minGoVersion, "min_go", "", "if set, the minimum go1.X version required for this test")
	return flags
}

func (t *markerTest) getGolden(id string) *Golden {
	golden, ok := t.golden[id]
	// If there was no golden content for this identifier, we must create one
	// to handle the case where -update is set: we need a place to store
	// the updated content.
	if !ok {
		golden = &Golden{id: id}

		// TODO(adonovan): the separation of markerTest (the
		// static aspects) from markerTestRun (the dynamic
		// ones) is evidently bogus because here we modify
		// markerTest during execution. Let's merge the two.
		t.golden[id] = golden
	}
	return golden
}

// Golden holds extracted golden content for a single @<name> prefix.
//
// When -update is set, golden captures the updated golden contents for later
// writing.
type Golden struct {
	id      string
	data    map[string][]byte // key "" => @id itself
	updated map[string][]byte
}

// Get returns golden content for the given name, which corresponds to the
// relative path following the golden prefix @<name>/. For example, to access
// the content of @foo/path/to/result.json from the Golden associated with
// @foo, name should be "path/to/result.json".
//
// If -update is set, the given update function will be called to get the
// updated golden content that should be written back to testdata.
//
// Marker functions must use this method instead of accessing data entries
// directly otherwise the -update operation will delete those entries.
//
// TODO(rfindley): rethink the logic here. We may want to separate Get and Set,
// and not delete golden content that isn't set.
func (g *Golden) Get(t testing.TB, name string, updated []byte) ([]byte, bool) {
	if existing, ok := g.updated[name]; ok {
		// Multiple tests may reference the same golden data, but if they do they
		// must agree about its expected content.
		if diff := compare.NamedText("existing", "updated", string(existing), string(updated)); diff != "" {
			t.Errorf("conflicting updates for golden data %s/%s:\n%s", g.id, name, diff)
		}
	}
	if g.updated == nil {
		g.updated = make(map[string][]byte)
	}
	g.updated[name] = updated
	if *update {
		return updated, true
	}

	res, ok := g.data[name]
	return res, ok
}

// loadMarkerTests walks the given dir looking for .txt files, which it
// interprets as a txtar archive.
//
// See the documentation for RunMarkerTests for more details on the test data
// archive.
//
// TODO(rfindley): this test could sanity check the results. For example, it is
// too easy to write "// @" instead of "//@", which we will happy skip silently.
func loadMarkerTests(dir string) ([]*markerTest, error) {
	var tests []*markerTest
	err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if strings.HasSuffix(path, ".txt") {
			content, err := os.ReadFile(path)
			if err != nil {
				return err
			}
			name := strings.TrimPrefix(path, dir+string(filepath.Separator))
			test, err := loadMarkerTest(name, content)
			if err != nil {
				return fmt.Errorf("%s: %v", path, err)
			}
			tests = append(tests, test)
		}
		return nil
	})
	return tests, err
}

func loadMarkerTest(name string, content []byte) (*markerTest, error) {
	archive := txtar.Parse(content)
	test := &markerTest{
		name:    name,
		fset:    token.NewFileSet(),
		content: content,
		archive: archive,
		files:   make(map[string][]byte),
		golden:  make(map[string]*Golden),
	}
	for _, file := range archive.Files {
		switch {
		case file.Name == "flags":
			test.flags = strings.Fields(string(file.Data))
			if err := test.flagSet().Parse(test.flags); err != nil {
				return nil, fmt.Errorf("parsing flags: %v", err)
			}

		case file.Name == "settings.json":
			if err := json.Unmarshal(file.Data, &test.settings); err != nil {
				return nil, err
			}

		case file.Name == "env":
			test.env = make(map[string]string)
			fields := strings.Fields(string(file.Data))
			for _, field := range fields {
				// TODO: use strings.Cut once we are on 1.18+.
				key, value, ok := cut(field, "=")
				if !ok {
					return nil, fmt.Errorf("env vars must be formatted as var=value, got %q", field)
				}
				test.env[key] = value
			}

		case strings.HasPrefix(file.Name, "@"): // golden content
			id, name, _ := cut(file.Name[len("@"):], "/")
			// Note that a file.Name of just "@id" gives (id, name) = ("id", "").
			if _, ok := test.golden[id]; !ok {
				test.golden[id] = &Golden{
					id:   id,
					data: make(map[string][]byte),
				}
			}
			test.golden[id].data[name] = file.Data

		default: // ordinary file content
			notes, err := expect.Parse(test.fset, file.Name, file.Data)
			if err != nil {
				return nil, fmt.Errorf("parsing notes in %q: %v", file.Name, err)
			}
			test.notes = append(test.notes, notes...)
			test.files[file.Name] = file.Data
		}
	}

	return test, nil
}

// cut is a copy of strings.Cut.
//
// TODO: once we only support Go 1.18+, just use strings.Cut.
func cut(s, sep string) (before, after string, found bool) {
	if i := strings.Index(s, sep); i >= 0 {
		return s[:i], s[i+len(sep):], true
	}
	return s, "", false
}

// formatTest formats the test as a txtar archive.
func formatTest(test *markerTest) ([]byte, error) {
	arch := &txtar.Archive{
		Comment: test.archive.Comment,
	}

	updatedGolden := make(map[string][]byte)
	for id, g := range test.golden {
		for name, data := range g.updated {
			filename := "@" + path.Join(id, name) // name may be ""
			updatedGolden[filename] = data
		}
	}

	// Preserve the original ordering of archive files.
	for _, file := range test.archive.Files {
		switch file.Name {
		// Preserve configuration files exactly as they were. They must have parsed
		// if we got this far.
		case "flags", "settings.json", "env":
			arch.Files = append(arch.Files, file)
		default:
			if _, ok := test.files[file.Name]; ok { // ordinary file
				arch.Files = append(arch.Files, file)
			} else if data, ok := updatedGolden[file.Name]; ok { // golden file
				arch.Files = append(arch.Files, txtar.File{Name: file.Name, Data: data})
				delete(updatedGolden, file.Name)
			}
		}
	}

	// ...followed by any new golden files.
	var newGoldenFiles []txtar.File
	for filename, data := range updatedGolden {
		newGoldenFiles = append(newGoldenFiles, txtar.File{Name: filename, Data: data})
	}
	// Sort new golden files lexically.
	sort.Slice(newGoldenFiles, func(i, j int) bool {
		return newGoldenFiles[i].Name < newGoldenFiles[j].Name
	})
	arch.Files = append(arch.Files, newGoldenFiles...)

	return txtar.Format(arch), nil
}

// newEnv creates a new environment for a marker test.
//
// TODO(rfindley): simplify and refactor the construction of testing
// environments across regtests, marker tests, and benchmarks.
func newEnv(t *testing.T, cache *cache.Cache, files map[string][]byte, config fake.EditorConfig) *Env {
	sandbox, err := fake.NewSandbox(&fake.SandboxConfig{
		RootDir: t.TempDir(),
		GOPROXY: "https://proxy.golang.org",
		Files:   files,
	})
	if err != nil {
		t.Fatal(err)
	}

	// Put a debug instance in the context to prevent logging to stderr.
	// See associated TODO in runner.go: we should revisit this pattern.
	ctx := context.Background()
	ctx = debug.WithInstance(ctx, "", "off")

	awaiter := NewAwaiter(sandbox.Workdir)
	ss := lsprpc.NewStreamServer(cache, false, hooks.Options)
	server := servertest.NewPipeServer(ss, jsonrpc2.NewRawStream)
	const skipApplyEdits = true // capture edits but don't apply them
	editor, err := fake.NewEditor(sandbox, config).Connect(ctx, server, awaiter.Hooks(), skipApplyEdits)
	if err != nil {
		sandbox.Close() // ignore error
		t.Fatal(err)
	}
	if err := awaiter.Await(ctx, InitialWorkspaceLoad); err != nil {
		sandbox.Close() // ignore error
		t.Fatal(err)
	}
	return &Env{
		T:       t,
		Ctx:     ctx,
		Editor:  editor,
		Sandbox: sandbox,
		Awaiter: awaiter,
	}
}

// A markerFunc is a reflectively callable @mark implementation function.
type markerFunc struct {
	fn         reflect.Value  // the func to invoke
	paramTypes []reflect.Type // parameter types, for zero values
	converters []converter    // to convert non-blank arguments
	variadic   bool
}

// A markerTestRun holds the state of one run of a marker test archive.
type markerTestRun struct {
	test *markerTest
	env  *Env

	// Collected information.
	// Each @diag/@suggestedfix marker eliminates an entry from diags.
	locations map[expect.Identifier]protocol.Location
	diags     map[protocol.Location][]protocol.Diagnostic
}

// sprintf returns a formatted string after applying pre-processing to
// arguments of the following types:
//   - token.Pos: formatted using (*markerTestRun).fmtPos
//   - protocol.Location: formatted using (*markerTestRun).fmtLoc
func (c *marker) sprintf(format string, args ...interface{}) string {
	if false {
		_ = fmt.Sprintf(format, args...) // enable vet printf checker
	}
	var args2 []interface{}
	for _, arg := range args {
		switch arg := arg.(type) {
		case token.Pos:
			args2 = append(args2, c.run.fmtPos(arg))
		case protocol.Location:
			args2 = append(args2, c.run.fmtLoc(arg))
		default:
			args2 = append(args2, arg)
		}
	}
	return fmt.Sprintf(format, args2...)
}

// fmtLoc formats the given pos in the context of the test, using
// archive-relative paths for files and including the line number in the full
// archive file.
func (run *markerTestRun) fmtPos(pos token.Pos) string {
	file := run.test.fset.File(pos)
	if file == nil {
		run.env.T.Errorf("position %d not in test fileset", pos)
		return "<invalid location>"
	}
	m, err := run.env.Editor.Mapper(file.Name())
	if err != nil {
		run.env.T.Errorf("%s", err)
		return "<invalid location>"
	}
	loc, err := m.PosLocation(file, pos, pos)
	if err != nil {
		run.env.T.Errorf("Mapper(%s).PosLocation failed: %v", file.Name(), err)
	}
	return run.fmtLoc(loc)
}

// fmtLoc formats the given location in the context of the test, using
// archive-relative paths for files and including the line number in the full
// archive file.
func (run *markerTestRun) fmtLoc(loc protocol.Location) string {
	if loc == (protocol.Location{}) {
		return "<missing location>"
	}
	lines := bytes.Count(run.test.archive.Comment, []byte("\n"))
	var name string
	for _, f := range run.test.archive.Files {
		lines++ // -- separator --
		uri := run.env.Sandbox.Workdir.URI(f.Name)
		if uri == loc.URI {
			name = f.Name
			break
		}
		lines += bytes.Count(f.Data, []byte("\n"))
	}
	if name == "" {
		run.env.T.Errorf("unable to find %s in test archive", loc)
		return "<invalid location>"
	}
	m, err := run.env.Editor.Mapper(name)
	if err != nil {
		run.env.T.Errorf("internal error: %v", err)
		return "<invalid location>"
	}
	s, err := m.LocationSpan(loc)
	if err != nil {
		run.env.T.Errorf("error formatting location %s: %v", loc, err)
		return "<invalid location>"
	}

	innerSpan := fmt.Sprintf("%d:%d", s.Start().Line(), s.Start().Column())       // relative to the embedded file
	outerSpan := fmt.Sprintf("%d:%d", lines+s.Start().Line(), s.Start().Column()) // relative to the archive file
	if s.Start() != s.End() {
		if s.End().Line() == s.Start().Line() {
			innerSpan += fmt.Sprintf("-%d", s.End().Column())
			outerSpan += fmt.Sprintf("-%d", s.End().Column())
		} else {
			innerSpan += fmt.Sprintf("-%d:%d", s.End().Line(), s.End().Column())
			innerSpan += fmt.Sprintf("-%d:%d", lines+s.End().Line(), s.End().Column())
		}
	}

	return fmt.Sprintf("%s:%s (%s:%s)", name, innerSpan, run.test.name, outerSpan)
}

// makeMarkerFunc uses reflection to create a markerFunc for the given func value.
func makeMarkerFunc(fn interface{}) markerFunc {
	mi := markerFunc{
		fn: reflect.ValueOf(fn),
	}
	mtyp := mi.fn.Type()
	mi.variadic = mtyp.IsVariadic()
	if mtyp.NumIn() == 0 || mtyp.In(0) != markerType {
		panic(fmt.Sprintf("marker function %#v must accept marker as its first argument", mi.fn))
	}
	if mtyp.NumOut() != 0 {
		panic(fmt.Sprintf("marker function %#v must not have results", mi.fn))
	}
	for a := 1; a < mtyp.NumIn(); a++ {
		in := mtyp.In(a)
		if mi.variadic && a == mtyp.NumIn()-1 {
			in = in.Elem() // for ...T, convert to T
		}
		mi.paramTypes = append(mi.paramTypes, in)
		c := makeConverter(in)
		mi.converters = append(mi.converters, c)
	}
	return mi
}

// ---- converters ----

// converter is the signature of argument converters.
// A converter should return an error rather than calling marker.errorf().
type converter func(marker, interface{}) (interface{}, error)

// Types with special conversions.
var (
	goldenType    = reflect.TypeOf(&Golden{})
	locationType  = reflect.TypeOf(protocol.Location{})
	markerType    = reflect.TypeOf(marker{})
	regexpType    = reflect.TypeOf(&regexp.Regexp{})
	wantErrorType = reflect.TypeOf(wantError{})
)

func makeConverter(paramType reflect.Type) converter {
	switch paramType {
	case goldenType:
		return goldenConverter
	case locationType:
		return locationConverter
	case wantErrorType:
		return wantErrorConverter
	default:
		return func(_ marker, arg interface{}) (interface{}, error) {
			if argType := reflect.TypeOf(arg); argType != paramType {
				return nil, fmt.Errorf("cannot convert type %s to %s", argType, paramType)
			}
			return arg, nil
		}
	}
}

// locationConverter converts a string argument into the protocol location
// corresponding to the first position of the string in the line preceding the
// note.
func locationConverter(mark marker, arg interface{}) (interface{}, error) {
	switch arg := arg.(type) {
	case string:
		startOff, preceding, m, err := linePreceding(mark.run, mark.note.Pos)
		if err != nil {
			return protocol.Location{}, err
		}
		idx := bytes.Index(preceding, []byte(arg))
		if idx < 0 {
			return nil, fmt.Errorf("substring %q not found in %q", arg, preceding)
		}
		off := startOff + idx
		return m.OffsetLocation(off, off+len(arg))
	case *regexp.Regexp:
		return findRegexpInLine(mark.run, mark.note.Pos, arg)
	case expect.Identifier:
		loc, ok := mark.run.locations[arg]
		if !ok {
			return nil, fmt.Errorf("no location named %q", arg)
		}
		return loc, nil
	default:
		return nil, fmt.Errorf("cannot convert argument type %T to location (must be a string to match the preceding line)", arg)
	}
}

// findRegexpInLine searches the partial line preceding pos for a match for the
// regular expression re, returning a location spanning the first match. If re
// contains exactly one subgroup, the position of this subgroup match is
// returned rather than the position of the full match.
func findRegexpInLine(run *markerTestRun, pos token.Pos, re *regexp.Regexp) (protocol.Location, error) {
	startOff, preceding, m, err := linePreceding(run, pos)
	if err != nil {
		return protocol.Location{}, err
	}

	matches := re.FindSubmatchIndex(preceding)
	if len(matches) == 0 {
		return protocol.Location{}, fmt.Errorf("no match for regexp %q found in %q", re, string(preceding))
	}
	var start, end int
	switch len(matches) {
	case 2:
		// no subgroups: return the range of the regexp expression
		start, end = matches[0], matches[1]
	case 4:
		// one subgroup: return its range
		start, end = matches[2], matches[3]
	default:
		return protocol.Location{}, fmt.Errorf("invalid location regexp %q: expect either 0 or 1 subgroups, got %d", re, len(matches)/2-1)
	}

	return m.OffsetLocation(start+startOff, end+startOff)
}

func linePreceding(run *markerTestRun, pos token.Pos) (int, []byte, *protocol.Mapper, error) {
	file := run.test.fset.File(pos)
	posn := safetoken.Position(file, pos)
	lineStart := file.LineStart(posn.Line)
	startOff, endOff, err := safetoken.Offsets(file, lineStart, pos)
	if err != nil {
		return 0, nil, nil, err
	}
	m, err := run.env.Editor.Mapper(file.Name())
	if err != nil {
		return 0, nil, nil, err
	}
	return startOff, m.Content[startOff:endOff], m, nil
}

// wantErrorConverter converts a string, regexp, or identifier
// argument into a wantError. The string is a substring of the
// expected error, the regexp is a pattern than matches the expected
// error, and the identifier is a golden file containing the expected
// error.
func wantErrorConverter(mark marker, arg interface{}) (interface{}, error) {
	switch arg := arg.(type) {
	case string:
		return wantError{substr: arg}, nil
	case *regexp.Regexp:
		return wantError{pattern: arg}, nil
	case expect.Identifier:
		golden := mark.run.test.getGolden(string(arg))
		return wantError{golden: golden}, nil
	default:
		return nil, fmt.Errorf("cannot convert %T to wantError (want: string, regexp, or identifier)", arg)
	}
}

// A wantError represents an expectation of a specific error message.
//
// It may be indicated in one of three ways, in 'expect' notation:
// - an identifier 'foo', to compare with the contents of the golden section @foo;
// - a pattern expression re"ab.*c", to match against a regular expression;
// - a string literal "abc", to check for a substring.
type wantError struct {
	golden  *Golden
	pattern *regexp.Regexp
	substr  string
}

func (we wantError) String() string {
	if we.golden != nil {
		return fmt.Sprintf("error from @%s entry", we.golden.id)
	} else if we.pattern != nil {
		return fmt.Sprintf("error matching %#q", we.pattern)
	} else {
		return fmt.Sprintf("error with substring %q", we.substr)
	}
}

// check asserts that 'err' matches the wantError's expectations.
func (we wantError) check(mark marker, err error) {
	if err == nil {
		mark.errorf("@%s succeeded unexpectedly, want %v", mark.note.Name, we)
		return
	}
	got := err.Error()

	if we.golden != nil {
		// Error message must match @id golden file.
		wantBytes, ok := we.golden.Get(mark.run.env.T, "", []byte(got))
		if !ok {
			mark.errorf("@%s: missing @%s entry", mark.note.Name, we.golden.id)
			return
		}
		want := strings.TrimSpace(string(wantBytes))
		if got != want {
			// (ignore leading/trailing space)
			mark.errorf("@%s failed with wrong error: got:\n%s\nwant:\n%s\ndiff:\n%s",
				mark.note.Name, got, want, compare.Text(want, got))
		}

	} else if we.pattern != nil {
		// Error message must match regular expression pattern.
		if !we.pattern.MatchString(got) {
			mark.errorf("got error %q, does not match pattern %#q", got, we.pattern)
		}

	} else if !strings.Contains(got, we.substr) {
		// Error message must contain expected substring.
		mark.errorf("got error %q, want substring %q", got, we.substr)
	}
}

// goldenConverter converts an identifier into the Golden directory of content
// prefixed by @<ident> in the test archive file.
func goldenConverter(mark marker, arg interface{}) (interface{}, error) {
	switch arg := arg.(type) {
	case expect.Identifier:
		return mark.run.test.getGolden(string(arg)), nil
	default:
		return nil, fmt.Errorf("invalid input type %T: golden key must be an identifier", arg)
	}
}

// checkChangedFiles compares the files changed by an operation with their expected (golden) state.
func checkChangedFiles(mark marker, changed map[string][]byte, golden *Golden) {
	// Check changed files match expectations.
	for filename, got := range changed {
		if want, ok := golden.Get(mark.run.env.T, filename, got); !ok {
			mark.errorf("%s: unexpected change to file %s; got:\n%s",
				mark.note.Name, filename, got)

		} else if string(got) != string(want) {
			mark.errorf("%s: wrong file content for %s: got:\n%s\nwant:\n%s\ndiff:\n%s",
				mark.note.Name, filename, got, want,
				compare.Bytes(want, got))
		}
	}

	// Report unmet expectations.
	for filename := range golden.data {
		if _, ok := changed[filename]; !ok {
			want, _ := golden.Get(mark.run.env.T, filename, nil)
			mark.errorf("%s: missing change to file %s; want:\n%s",
				mark.note.Name, filename, want)
		}
	}
}

// ---- marker functions ----

// completeMarker implements the @complete marker, running
// textDocument/completion at the given src location and asserting that the
// results match the expected results.
//
// TODO(rfindley): for now, this is just a quick check against the expected
// completion labels. We could do more by assembling richer completion items,
// as is done in the old marker tests. Does that add value? If so, perhaps we
// should support a variant form of the argument, labelOrItem, which allows the
// string form or item form.
func completeMarker(mark marker, src protocol.Location, want ...string) {
	list := mark.run.env.Completion(src)
	var got []string
	for _, item := range list.Items {
		got = append(got, item.Label)
	}
	if diff := cmp.Diff(want, got); diff != "" {
		mark.errorf("Completion(...) returned unexpect results (-want +got):\n%s", diff)
	}
}

// defMarker implements the @godef marker, running textDocument/definition at
// the given src location and asserting that there is exactly one resulting
// location, matching dst.
//
// TODO(rfindley): support a variadic destination set.
func defMarker(mark marker, src, dst protocol.Location) {
	got := mark.run.env.GoToDefinition(src)
	if got != dst {
		mark.errorf("definition location does not match:\n\tgot: %s\n\twant %s",
			mark.run.fmtLoc(got), mark.run.fmtLoc(dst))
	}
}

// hoverMarker implements the @hover marker, running textDocument/hover at the
// given src location and asserting that the resulting hover is over the dst
// location (typically a span surrounding src), and that the markdown content
// matches the golden content.
func hoverMarker(mark marker, src, dst protocol.Location, golden *Golden) {
	content, gotDst := mark.run.env.Hover(src)
	if gotDst != dst {
		mark.errorf("hover location does not match:\n\tgot: %s\n\twant %s)", mark.run.fmtLoc(gotDst), mark.run.fmtLoc(dst))
	}
	gotMD := ""
	if content != nil {
		gotMD = content.Value
	}
	wantMD := ""
	if golden != nil {
		wantBytes, _ := golden.Get(mark.run.env.T, "hover.md", []byte(gotMD))
		wantMD = string(wantBytes)
	}
	// Normalize newline termination: archive files can't express non-newline
	// terminated files.
	if strings.HasSuffix(wantMD, "\n") && !strings.HasSuffix(gotMD, "\n") {
		gotMD += "\n"
	}
	if diff := tests.DiffMarkdown(wantMD, gotMD); diff != "" {
		mark.errorf("hover markdown mismatch (-want +got):\n%s", diff)
	}
}

// locMarker implements the @loc marker. It is executed before other
// markers, so that locations are available.
func locMarker(mark marker, name expect.Identifier, loc protocol.Location) {
	if prev, dup := mark.run.locations[name]; dup {
		mark.errorf("location %q already declared at %s",
			name, mark.run.fmtLoc(prev))
		return
	}
	mark.run.locations[name] = loc
}

// diagMarker implements the @diag marker. It eliminates diagnostics from
// the observed set in mark.test.
func diagMarker(mark marker, loc protocol.Location, re *regexp.Regexp) {
	if _, err := removeDiagnostic(mark, loc, re); err != nil {
		mark.errorf("%v", err)
	}
}

func removeDiagnostic(mark marker, loc protocol.Location, re *regexp.Regexp) (protocol.Diagnostic, error) {
	diags := mark.run.diags[loc]
	for i, diag := range diags {
		if re.MatchString(diag.Message) {
			mark.run.diags[loc] = append(diags[:i], diags[i+1:]...)
			return diag, nil
		}
	}
	return protocol.Diagnostic{}, errors.New(mark.sprintf("no diagnostic at %v matches %q", loc, re))
}

// renameMarker implements the @rename(location, new, golden) marker.
func renameMarker(mark marker, loc protocol.Location, newName expect.Identifier, golden *Golden) {
	changed, err := rename(mark.run.env, loc, string(newName))
	if err != nil {
		mark.errorf("rename failed: %v. (Use @renameerr for expected errors.)", err)
		return
	}
	checkChangedFiles(mark, changed, golden)
}

// renameErrMarker implements the @renamererr(location, new, error) marker.
func renameErrMarker(mark marker, loc protocol.Location, newName expect.Identifier, wantErr wantError) {
	_, err := rename(mark.run.env, loc, string(newName))
	wantErr.check(mark, err)
}

// rename returns the new contents of the files that would be modified
// by renaming the identifier at loc to newName.
func rename(env *Env, loc protocol.Location, newName string) (map[string][]byte, error) {
	// We call Server.Rename directly, instead of
	//   env.Editor.Rename(env.Ctx, loc, newName)
	// to isolate Rename from PrepareRename, and because we don't
	// want to modify the file system in a scenario with multiple
	// @rename markers.

	editMap, err := env.Editor.Server.Rename(env.Ctx, &protocol.RenameParams{
		TextDocument: protocol.TextDocumentIdentifier{URI: loc.URI},
		Position:     loc.Range.Start,
		NewName:      string(newName),
	})
	if err != nil {
		return nil, err
	}

	return applyDocumentChanges(env, editMap.DocumentChanges)
}

// applyDocumentChanges returns the effect of applying the document
// changes to the contents of the Editor buffers. The actual editor
// buffers are unchanged.
func applyDocumentChanges(env *Env, changes []protocol.DocumentChanges) (map[string][]byte, error) {
	result := make(map[string][]byte)
	for _, change := range changes {
		if change.RenameFile != nil {
			// rename
			oldFile := env.Sandbox.Workdir.URIToPath(change.RenameFile.OldURI)
			newFile := env.Sandbox.Workdir.URIToPath(change.RenameFile.NewURI)
			mapper, err := env.Editor.Mapper(oldFile)
			if err != nil {
				return nil, err
			}
			result[newFile] = mapper.Content

		} else {
			// edit
			filename := env.Sandbox.Workdir.URIToPath(change.TextDocumentEdit.TextDocument.URI)
			mapper, err := env.Editor.Mapper(filename)
			if err != nil {
				return nil, err
			}
			patched, _, err := source.ApplyProtocolEdits(mapper, change.TextDocumentEdit.Edits)
			if err != nil {
				return nil, err
			}
			result[filename] = patched
		}
	}

	return result, nil
}

// suggestedfixMarker implements the @suggestedfix(location, regexp,
// kind, golden) marker. It acts like @diag(location, regexp), to set
// the expectation of a diagnostic, but then it applies the first code
// action of the specified kind suggested by the matched diagnostic.
func suggestedfixMarker(mark marker, loc protocol.Location, re *regexp.Regexp, actionKind string, golden *Golden) {
	// Find and remove the matching diagnostic.
	diag, err := removeDiagnostic(mark, loc, re)
	if err != nil {
		mark.errorf("%v", err)
		return
	}

	// Apply the fix it suggests.
	changed, err := suggestedfix(mark.run.env, loc, diag, actionKind)
	if err != nil {
		mark.errorf("suggestedfix failed: %v. (Use @suggestedfixerr for expected errors.)", err)
		return
	}

	// Check the file state.
	checkChangedFiles(mark, changed, golden)
}

func suggestedfix(env *Env, loc protocol.Location, diag protocol.Diagnostic, actionKind string) (map[string][]byte, error) {

	// Request all code actions that apply to the diagnostic.
	// (The protocol supports filtering using Context.Only={actionKind}
	// but we can give a better error if we don't filter.)
	actions, err := env.Editor.Server.CodeAction(env.Ctx, &protocol.CodeActionParams{
		TextDocument: protocol.TextDocumentIdentifier{URI: loc.URI},
		Range:        diag.Range,
		Context: protocol.CodeActionContext{
			Only:        nil, // => all kinds
			Diagnostics: []protocol.Diagnostic{diag},
		},
	})
	if err != nil {
		return nil, err
	}

	// Find the sole candidates CodeAction of the specified kind (e.g. refactor.rewrite).
	var candidates []protocol.CodeAction
	for _, act := range actions {
		if act.Kind == protocol.CodeActionKind(actionKind) {
			candidates = append(candidates, act)
		}
	}
	if len(candidates) != 1 {
		for _, act := range actions {
			env.T.Logf("found CodeAction Kind=%s Title=%q", act.Kind, act.Title)
		}
		return nil, fmt.Errorf("found %d CodeActions of kind %s for this diagnostic, want 1", len(candidates), actionKind)
	}
	action := candidates[0]

	// An action may specify an edit and/or a command, to be
	// applied in that order. But since applyDocumentChanges(env,
	// action.Edit.DocumentChanges) doesn't compose, for now we
	// assert that all commands used in the @suggestedfix tests
	// return only a command.
	if action.Edit.DocumentChanges != nil {
		env.T.Errorf("internal error: discarding unexpected CodeAction{Kind=%s, Title=%q}.Edit.DocumentChanges", action.Kind, action.Title)
	}
	if action.Command == nil {
		return nil, fmt.Errorf("missing CodeAction{Kind=%s, Title=%q}.Command", action.Kind, action.Title)
	}

	// This is a typical CodeAction command:
	//
	//   Title:     "Implement error"
	//   Command:   gopls.apply_fix
	//   Arguments: [{"Fix":"stub_methods","URI":".../a.go","Range":...}}]
	//
	// The client makes an ExecuteCommand RPC to the server,
	// which dispatches it to the ApplyFix handler.
	// ApplyFix dispatches to the "stub_methods" suggestedfix hook (the meat).
	// The server then makes an ApplyEdit RPC to the client,
	// whose Awaiter hook gathers the edits instead of applying them.

	_ = env.Awaiter.takeDocumentChanges() // reset (assuming Env is confined to this thread)

	if _, err := env.Editor.Server.ExecuteCommand(env.Ctx, &protocol.ExecuteCommandParams{
		Command:   action.Command.Command,
		Arguments: action.Command.Arguments,
	}); err != nil {
		env.T.Fatalf("error converting command %q to edits: %v", action.Command.Command, err)
	}

	return applyDocumentChanges(env, env.Awaiter.takeDocumentChanges())
}

// TODO(adonovan): suggestedfixerr

// refsMarker implements the @refs marker.
func refsMarker(mark marker, src protocol.Location, want ...protocol.Location) {
	refs := func(includeDeclaration bool, want []protocol.Location) error {
		params := &protocol.ReferenceParams{
			TextDocumentPositionParams: protocol.LocationTextDocumentPositionParams(src),
			Context: protocol.ReferenceContext{
				IncludeDeclaration: includeDeclaration,
			},
		}

		got, err := mark.run.env.Editor.Server.References(mark.run.env.Ctx, params)
		if err != nil {
			return err
		}

		// Compare the sets of locations.
		toString := func(locs []protocol.Location) string {
			// TODO(adonovan): use generic JoinValues(locs, fmtLoc).
			strs := make([]string, len(locs))
			for i, loc := range locs {
				strs[i] = mark.run.fmtLoc(loc)
			}
			sort.Strings(strs)
			return strings.Join(strs, "\n")
		}
		gotStr := toString(got)
		wantStr := toString(want)
		if gotStr != wantStr {
			return fmt.Errorf("incorrect references (got %d, want %d) at %s:\n%s",
				len(got), len(want),
				mark.run.fmtLoc(src),
				diff.Unified("want", "got", wantStr, gotStr))
		}
		return nil
	}

	for _, includeDeclaration := range []bool{false, true} {
		// Ignore first 'want' location if we didn't request the declaration.
		// TODO(adonovan): don't assume a single declaration:
		// there may be >1 if corresponding methods are considered.
		want := want
		if !includeDeclaration && len(want) > 0 {
			want = want[1:]
		}
		if err := refs(includeDeclaration, want); err != nil {
			mark.errorf("refs(includeDeclaration=%t) failed: %v",
				includeDeclaration, err)
		}
	}
}