internal/lsp/source: propose exports for unimported packages

When a user completes rand.<>, propose rand.Seed (from math/rand) and
rand.Prime (from crypto/rand), etc.

Because we don't necessarily have type checking information for
unimported packages, I had to add shortcut cases to a number of
functions around the completion code. Better suggestions welcome.

Change-Id: I7822dc75c86b24156963e7bdd959443f4f2748b1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/204819
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Muir Manders <muir@mnd.rs>

internal/lsp/source/completion.go

@@ -577,11 +577,24 @@ func (c *completer) selector(sel *ast.SelectorExpr) error {
 
 	// Invariant: sel is a true selector.
 	tv, ok := c.pkg.GetTypesInfo().Types[sel.X]
-	if !ok {
-		return errors.Errorf("cannot resolve %s", sel.X)
+	if ok {
+		return c.methodsAndFields(tv.Type, tv.Addressable(), nil)
 	}
 
-	return c.methodsAndFields(tv.Type, tv.Addressable(), nil)
+	// Try unimported packages.
+	if id, ok := sel.X.(*ast.Ident); ok {
+		pkgExports, err := PackageExports(c.ctx, c.view, id.Name, c.filename)
+		if err != nil {
+			return err
+		}
+		for _, pkgExport := range pkgExports {
+			pkg := types.NewPackage(pkgExport.Fix.StmtInfo.ImportPath, pkgExport.Fix.IdentName)
+			for _, export := range pkgExport.Exports {
+				c.found(types.NewVar(0, pkg, export, nil), 0.07, &pkgExport.Fix.StmtInfo)
+			}
+		}
+	}
+	return nil
 }
 
 func (c *completer) packageMembers(pkg *types.Package, imp *imports.ImportInfo) {
@@ -1347,6 +1360,9 @@ func (c *completer) matchingCandidate(cand *candidate) bool {
 	}
 
 	objType := cand.obj.Type()
+	if objType == nil {
+		return true
+	}
 
 	// Default to invoking *types.Func candidates. This is so function
 	// completions in an empty statement (or other cases with no expected type)

internal/lsp/source/completion_format.go

@@ -39,6 +39,9 @@ func (c *completer) item(cand candidate) (CompletionItem, error) {
 		snip          *snippet.Builder
 		protocolEdits []protocol.TextEdit
 	)
+	if obj.Type() == nil {
+		detail = ""
+	}
 
 	// expandFuncCall mutates the completion label, detail, and snippet
 	// to that of an invocation of sig.
@@ -64,6 +67,9 @@ func (c *completer) item(cand candidate) (CompletionItem, error) {
 		} else {
 			kind = protocol.VariableCompletion
 		}
+		if obj.Type() == nil {
+			break
+		}
 
 		if sig, ok := obj.Type().Underlying().(*types.Signature); ok && cand.expandFuncCall {
 			expandFuncCall(sig)
@@ -91,11 +97,20 @@ func (c *completer) item(cand candidate) (CompletionItem, error) {
 
 	// If this candidate needs an additional import statement,
 	// add the additional text edits needed.
+	if cand.imp != nil {
 		addlEdits, err := c.importEdits(cand.imp)
 		if err != nil {
 			return CompletionItem{}, err
 		}
+
 		protocolEdits = append(protocolEdits, addlEdits...)
+		if kind != protocol.ModuleCompletion {
+			if detail != "" {
+				detail += " "
+			}
+			detail += fmt.Sprintf("(from %q)", cand.imp.ImportPath)
+		}
+	}
 
 	detail = strings.TrimPrefix(detail, "untyped ")
 	item := CompletionItem{
@@ -146,7 +161,7 @@ func (c *completer) item(cand candidate) (CompletionItem, error) {
 	return item, nil
 }
 
-// importEdits produces the text eddits necessary to add the given import to the current file.
+// importEdits produces the text edits necessary to add the given import to the current file.
 func (c *completer) importEdits(imp *imports.ImportInfo) ([]protocol.TextEdit, error) {
 	if imp == nil {
 		return nil, nil

internal/lsp/source/deep_completion.go

@@ -158,6 +158,10 @@ func (c *completer) deepSearch(obj types.Object, imp *imports.ImportInfo) {
 		return
 	}
 
+	if obj.Type() == nil {
+		return
+	}
+
 	// Don't search embedded fields because they were already included in their
 	// parent's fields.
 	if v, ok := obj.(*types.Var); ok && v.Embedded() {

internal/lsp/source/format.go

@@ -240,11 +240,8 @@ func AllImportsFixes(ctx context.Context, view View, f File) (edits []protocol.T
 	return edits, editsPerFix, nil
 }
 
-// AllImportsFixes formats f for each possible fix to the imports.
-// In addition to returning the result of applying all edits,
-// it returns a list of fixes that could be applied to the file, with the
-// corresponding TextEdits that would be needed to apply that fix.
-func CandidateImports(ctx context.Context, view View, filename string) (pkgs []imports.ImportFix, err error) {
+// CandidateImports returns every import that could be added to filename.
+func CandidateImports(ctx context.Context, view View, filename string) ([]imports.ImportFix, error) {
 	ctx, done := trace.StartSpan(ctx, "source.CandidateImports")
 	defer done()
 
@@ -257,16 +254,41 @@ func CandidateImports(ctx context.Context, view View, filename string) (pkgs []i
 		TabIndent:  true,
 		TabWidth:   8,
 	}
+
+	var imps []imports.ImportFix
 	importFn := func(opts *imports.Options) error {
-		pkgs, err = imports.GetAllCandidates(filename, opts)
+		var err error
+		imps, err = imports.GetAllCandidates(filename, opts)
 		return err
 	}
-	err = view.RunProcessEnvFunc(ctx, importFn, options)
-	if err != nil {
-		return nil, err
+	err := view.RunProcessEnvFunc(ctx, importFn, options)
+	return imps, err
 }
 
-	return pkgs, nil
+// PackageExports returns all the packages named pkg that could be imported by
+// filename, and their exports.
+func PackageExports(ctx context.Context, view View, pkg, filename string) ([]imports.PackageExport, error) {
+	ctx, done := trace.StartSpan(ctx, "source.PackageExports")
+	defer done()
+
+	options := &imports.Options{
+		// Defaults.
+		AllErrors:  true,
+		Comments:   true,
+		Fragment:   true,
+		FormatOnly: false,
+		TabIndent:  true,
+		TabWidth:   8,
+	}
+
+	var pkgs []imports.PackageExport
+	importFn := func(opts *imports.Options) error {
+		var err error
+		pkgs, err = imports.GetPackageExports(pkg, filename, opts)
+		return err
+	}
+	err := view.RunProcessEnvFunc(ctx, importFn, options)
+	return pkgs, err
 }
 
 // hasParseErrors returns true if the given file has parse errors.

internal/lsp/testdata/summary.txt.golden

@@ -1,7 +1,7 @@
 -- summary --
 CompletionsCount = 213
 CompletionSnippetCount = 40
-UnimportedCompletionsCount = 1
+UnimportedCompletionsCount = 2
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 7
 RankedCompletionsCount = 8

internal/lsp/testdata/unimported/unimported.go.in

@@ -2,6 +2,7 @@ package unimported
 
 func _() {
 	//@unimported("", bytes, context, cryptoslashrand, time, unsafe, externalpackage)
+	bytes. //@unimported(" /", bytesbuffer)
 }
 
 // Create markers for unimported std lib packages. Only for use by this test.
@@ -11,3 +12,5 @@ func _() {
 /* time */ //@item(time, "time", "\"time\"", "package")
 /* unsafe */ //@item(unsafe, "unsafe", "\"unsafe\"", "package")
 /* pkg */ //@item(externalpackage, "pkg", "\"example.com/extramodule/pkg\"", "package" )
+
+/* bytes.Buffer */ //@item(bytesbuffer, "Buffer", "(from \"bytes\")", "var" )

internal/lsp/tests/completion.go

@@ -19,7 +19,7 @@ func ToProtocolCompletionItems(items []source.CompletionItem) []protocol.Complet
 }
 
 func ToProtocolCompletionItem(item source.CompletionItem) protocol.CompletionItem {
-	return protocol.CompletionItem{
+	pItem := protocol.CompletionItem{
 		Label:         item.Label,
 		Kind:          item.Kind,
 		Detail:        item.Detail,
@@ -29,6 +29,10 @@ func ToProtocolCompletionItem(item source.CompletionItem) protocol.CompletionIte
 			NewText: item.Snippet(),
 		},
 	}
+	if pItem.InsertText == "" {
+		pItem.InsertText = pItem.Label
+	}
+	return pItem
 }
 
 func FilterBuiltins(items []protocol.CompletionItem) []protocol.CompletionItem {