internal/lsp/completion: indicate completion candidates that are deprecated

In LSP, CompletionItems can say if they are for deprecated names. This
CL implements that for items where the doc comments contain a line
starting // Deprecated.

Semantic tokens now similarly mark deprecated tokens, but in vscode
the default theme doesn't change the display, and the customization
options seem limited to:

    "editor.semanticTokenColorCustomizations": {
        "rules": {
          // only foreground, bold, underline, italic
          "*.deprecated": {"italic": true}
        }
    },

Change-Id: I93ccc227bf4e1e30a4f23b40da4d2cbafe1cd925
Reviewed-on: https://go-review.googlesource.com/c/tools/+/313509
Run-TryBot: Peter Weinberger <pjw@google.com>
Trust: Peter Weinberger <pjw@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

gopls/internal/regtest/completion/completion_test.go

@@ -456,3 +456,50 @@ func _() {
 		}
 	})
 }
+
+func TestCompletionDeprecation(t *testing.T) {
+	const files = `
+-- go.mod --
+module test.com
+
+go 1.16
+-- prog.go --
+package waste
+// Deprecated, use newFoof
+func fooFunc() bool {
+	return false
+}
+
+// Deprecated
+const badPi = 3.14
+
+func doit() {
+	if fooF
+	panic()
+	x := badP
+}
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("prog.go")
+		pos := env.RegexpSearch("prog.go", "if fooF")
+		pos.Column += len("if fooF")
+		completions := env.Completion("prog.go", pos)
+		diff := compareCompletionResults([]string{"fooFunc"}, completions.Items)
+		if diff != "" {
+			t.Error(diff)
+		}
+		if completions.Items[0].Tags == nil {
+			t.Errorf("expected Tags to show deprecation %#v", diff[0])
+		}
+		pos = env.RegexpSearch("prog.go", "= badP")
+		pos.Column += len("= badP")
+		completions = env.Completion("prog.go", pos)
+		diff = compareCompletionResults([]string{"badPi"}, completions.Items)
+		if diff != "" {
+			t.Error(diff)
+		}
+		if completions.Items[0].Tags == nil {
+			t.Errorf("expected Tags to show deprecation %#v", diff[0])
+		}
+	})
+}

internal/lsp/completion.go

@@ -154,6 +154,8 @@ func toProtocolCompletionItems(candidates []completion.CompletionItem, rng proto
 
 			Preselect:     i == 0,
 			Documentation: candidate.Documentation,
+			Tags:          candidate.Tags,
+			Deprecated:    candidate.Deprecated,
 		}
 		items = append(items, item)
 	}

internal/lsp/fake/editor.go

@@ -270,6 +270,7 @@ func (e *Editor) initialize(ctx context.Context, workspaceFolders []string) erro
 	params.Capabilities.Workspace.Configuration = true
 	params.Capabilities.Window.WorkDoneProgress = true
 	// TODO: set client capabilities
+	params.Capabilities.TextDocument.Completion.CompletionItem.TagSupport.ValueSet = []protocol.CompletionItemTag{protocol.ComplDeprecated}
 	params.InitializationOptions = e.configuration()
 	if e.Config.SendPID {
 		params.ProcessID = int32(os.Getpid())

internal/lsp/semantic.go

@@ -22,7 +22,8 @@ import (
 	errors "golang.org/x/xerrors"
 )
 
-const maxFullFileSize int = 100000 // reject full semantic token requests for large files
+// reject full semantic token requests for large files
+const maxFullFileSize int = 100000
 
 func (s *Server) semanticTokensFull(ctx context.Context, p *protocol.SemanticTokensParams) (*protocol.SemanticTokens, error) {
 	ret, err := s.computeSemanticTokens(ctx, p.TextDocument, nil)
@@ -426,6 +427,18 @@ func (e *encoded) ident(x *ast.Ident) {
 	}
 }
 
+func isDeprecated(n *ast.CommentGroup) bool {
+	if n == nil {
+		return false
+	}
+	for _, c := range n.List {
+		if strings.HasPrefix(c.Text, "// Deprecated") {
+			return true
+		}
+	}
+	return false
+}
+
 func (e *encoded) definitionFor(x *ast.Ident) (tokenType, []string) {
 	mods := []string{"definition"}
 	for i := len(e.stack) - 1; i >= 0; i-- {
@@ -437,6 +450,9 @@ func (e *encoded) definitionFor(x *ast.Ident) (tokenType, []string) {
 			}
 			return "variable", mods
 		case *ast.GenDecl:
+			if isDeprecated(y.Doc) {
+				mods = append(mods, "deprecated")
+			}
 			if y.Tok == token.CONST {
 				mods = append(mods, "readonly")
 			}
@@ -444,6 +460,9 @@ func (e *encoded) definitionFor(x *ast.Ident) (tokenType, []string) {
 		case *ast.FuncDecl:
 			// If x is immediately under a FuncDecl, it is a function or method
 			if i == len(e.stack)-2 {
+				if isDeprecated(y.Doc) {
+					mods = append(mods, "deprecated")
+				}
 				if y.Recv != nil {
 					return tokMember, mods
 				}

internal/lsp/source/completion/completion.go

@@ -45,7 +45,9 @@ type CompletionItem struct {
 	// The insert text does not contain snippets.
 	InsertText string
 
-	Kind protocol.CompletionItemKind
+	Kind       protocol.CompletionItemKind
+	Tags       []protocol.CompletionItemTag
+	Deprecated bool // Deprecated, prefer Tags if available
 
 	// An optional array of additional TextEdits that are applied when
 	// selecting this completion.

internal/lsp/source/completion/format.go

@@ -243,6 +243,14 @@ func (c *completer) item(ctx context.Context, cand candidate) (CompletionItem, e
 	if c.opts.fullDocumentation {
 		item.Documentation = hover.FullDocumentation
 	}
+	// The desired pattern is `^// Deprecated`, but the prefix has been removed
+	if strings.HasPrefix(hover.FullDocumentation, "Deprecated") {
+		if c.snapshot.View().Options().CompletionTags {
+			item.Tags = []protocol.CompletionItemTag{protocol.ComplDeprecated}
+		} else if c.snapshot.View().Options().CompletionDeprecated {
+			item.Deprecated = true
+		}
+	}
 
 	return item, nil
 }

internal/lsp/source/options.go

@@ -188,6 +188,8 @@ type ClientOptions struct {
 	SemanticTypes                     []string
 	SemanticMods                      []string
 	RelatedInformationSupported       bool
+	CompletionTags                    bool
+	CompletionDeprecated              bool
 }
 
 // ServerOptions holds LSP-specific configuration that is provided by the
@@ -647,6 +649,12 @@ func (o *Options) ForClientCapabilities(caps protocol.ClientCapabilities) {
 
 	// Check if the client supports diagnostic related information.
 	o.RelatedInformationSupported = caps.TextDocument.PublishDiagnostics.RelatedInformation
+	// Check if the client completion support incliudes tags (preferred) or deprecation
+	if caps.TextDocument.Completion.CompletionItem.TagSupport.ValueSet != nil {
+		o.CompletionTags = true
+	} else if caps.TextDocument.Completion.CompletionItem.DeprecatedSupport {
+		o.CompletionDeprecated = true
+	}
 }
 
 func (o *Options) Clone() *Options {