tools/gopls: add cmd support for implementation

This change adds command line support for implementation.

Example:

$ gopls implementation ~/tmp/foo/main.go:8:6
$ gopls implementation ~/tmp/foo/main.go:#53

Updates golang/go#32875

Change-Id: I3aa89a788ded886368b07c1824325069f3cba88a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/208357
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cmd/cmd.go

@@ -145,6 +145,7 @@ func (app *Application) commands() []tool.Application {
 		&foldingRanges{app: app},
 		&format{app: app},
 		&links{app: app},
+		&implementation{app: app},
 		&imports{app: app},
 		&query{app: app},
 		&references{app: app},

internal/lsp/cmd/implementation.go

@@ -0,0 +1,89 @@
+// Copyright 2019 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 cmd
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"sort"
+
+	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/span"
+	"golang.org/x/tools/internal/tool"
+)
+
+// implementation implements the implementation verb for gopls
+type implementation struct {
+	app *Application
+}
+
+func (i *implementation) Name() string      { return "implementation" }
+func (i *implementation) Usage() string     { return "<position>" }
+func (i *implementation) ShortHelp() string { return "display selected identifier's implementation" }
+func (i *implementation) DetailedHelp(f *flag.FlagSet) {
+	fmt.Fprint(f.Output(), `
+Example:
+
+  $ # 1-indexed location (:line:column or :#offset) of the target identifier
+  $ gopls implementation helper/helper.go:8:6
+  $ gopls implementation helper/helper.go:#53
+
+  gopls implementation flags are:
+`)
+	f.PrintDefaults()
+}
+
+func (i *implementation) Run(ctx context.Context, args ...string) error {
+	if len(args) != 1 {
+		return tool.CommandLineErrorf("implementation expects 1 argument (position)")
+	}
+
+	conn, err := i.app.connect(ctx)
+	if err != nil {
+		return err
+	}
+	defer conn.terminate(ctx)
+
+	from := span.Parse(args[0])
+	file := conn.AddFile(ctx, from.URI())
+	if file.err != nil {
+		return file.err
+	}
+
+	loc, err := file.mapper.Location(from)
+	if err != nil {
+		return err
+	}
+
+	p := protocol.ImplementationParams{
+		TextDocumentPositionParams: protocol.TextDocumentPositionParams{
+			TextDocument: protocol.TextDocumentIdentifier{URI: loc.URI},
+			Position:     loc.Range.Start,
+		},
+	}
+
+	implementations, err := conn.Implementation(ctx, &p)
+	if err != nil {
+		return err
+	}
+
+	var spans []string
+	for _, impl := range implementations {
+		f := conn.AddFile(ctx, span.NewURI(impl.URI))
+		span, err := f.mapper.Span(impl)
+		if err != nil {
+			return err
+		}
+		spans = append(spans, fmt.Sprint(span))
+	}
+	sort.Strings(spans)
+
+	for _, s := range spans {
+		fmt.Println(s)
+	}
+
+	return nil
+}

internal/lsp/cmd/test/cmdtest.go

@@ -103,10 +103,6 @@ func (r *runner) PrepareRename(t *testing.T, src span.Span, want *source.Prepare
 	//TODO: add command line prepare rename tests when it works
 }
 
-func (r *runner) Implementation(t *testing.T, spn span.Span, imp tests.Implementations) {
-	//TODO: add implements tests when it works
-}
-
 func (r *runner) RunGoplsCmd(t testing.TB, args ...string) (string, string) {
 	rStdout, wStdout, err := os.Pipe()
 	if err != nil {

internal/lsp/cmd/test/implementation.go

@@ -0,0 +1,36 @@
+// Copyright 2019 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 cmdtest
+
+import (
+	"fmt"
+	"sort"
+	"testing"
+
+	"golang.org/x/tools/internal/lsp/tests"
+	"golang.org/x/tools/internal/span"
+)
+
+func (r *runner) Implementation(t *testing.T, spn span.Span, imp tests.Implementations) {
+	var itemStrings []string
+	for _, i := range imp.Implementations {
+		itemStrings = append(itemStrings, fmt.Sprint(i))
+	}
+	sort.Strings(itemStrings)
+	var expect string
+	for _, i := range itemStrings {
+		expect += i + "\n"
+	}
+	expect = r.Normalize(expect)
+
+	uri := spn.URI()
+	filename := uri.Filename()
+	target := filename + fmt.Sprintf(":%v:%v", spn.Start().Line(), spn.Start().Column())
+
+	got, _ := r.NormalizeGoplsCmd(t, "implementation", target)
+	if expect != got {
+		t.Errorf("implementation failed for %s expected:\n%s\ngot:\n%s", target, expect, got)
+	}
+}