internal/lsp/source: scan loaded packages first for completions

Packages that have already been loaded by gopls are more likely to be
used, and have full type information. Check them for completion
candidates before scanning the disk.

Also, minor bug fixes: add a missing mutex, and use a lower-than-usual
score for typed unimported completions.

Change-Id: I46388802913f9a89342fb47290f704b471154ec0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/212860
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/completion.go

@@ -617,7 +617,7 @@ func (c *completer) selector(sel *ast.SelectorExpr) error {
 	// Is sel a qualified identifier?
 	if id, ok := sel.X.(*ast.Ident); ok {
 		if pkgname, ok := c.pkg.GetTypesInfo().Uses[id].(*types.PkgName); ok {
-			c.packageMembers(pkgname.Imported(), nil)
+			c.packageMembers(pkgname.Imported(), stdScore, nil)
 			return nil
 		}
 	}
@@ -630,53 +630,71 @@ func (c *completer) selector(sel *ast.SelectorExpr) error {
 
 	// Try unimported packages.
 	if id, ok := sel.X.(*ast.Ident); ok && c.opts.Unimported && len(c.items) < unimportedTarget {
-		ctx, cancel := c.deepCompletionContext()
+		if err := c.unimportedMembers(id); err != nil {
-		defer cancel()
-
-		known := c.snapshot.KnownImportPaths()
-		add := func(pkgExport imports.PackageExport) {
-			// If we've seen this import path, use the fully-typed version.
-			if knownPkg, ok := known[pkgExport.Fix.StmtInfo.ImportPath]; ok {
-				c.packageMembers(knownPkg.GetTypes(), &importInfo{
-					importPath: pkgExport.Fix.StmtInfo.ImportPath,
-					name:       pkgExport.Fix.StmtInfo.Name,
-					pkg:        knownPkg,
-				})
-			} else {
-				// Otherwise, continue with untyped proposals.
-				pkg := types.NewPackage(pkgExport.Fix.StmtInfo.ImportPath, pkgExport.Fix.IdentName)
-				for _, export := range pkgExport.Exports {
-					score := 0.01 * float64(pkgExport.Fix.Relevance)
-					c.found(candidate{
-						obj:   types.NewVar(0, pkg, export, nil),
-						score: score,
-						imp: &importInfo{
-							importPath: pkgExport.Fix.StmtInfo.ImportPath,
-							name:       pkgExport.Fix.StmtInfo.Name,
-						},
-					})
-				}
-			}
-			if len(c.items) >= unimportedTarget {
-				cancel()
-			}
-		}
-		if err := c.snapshot.View().RunProcessEnvFunc(ctx, func(opts *imports.Options) error {
-			return imports.GetPackageExports(ctx, add, id.Name, c.filename, opts)
-		}); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-func (c *completer) packageMembers(pkg *types.Package, imp *importInfo) {
+func (c *completer) unimportedMembers(id *ast.Ident) error {
+	// Try loaded packages first. They're relevant, fast, and fully typed.
+	known := c.snapshot.KnownImportPaths()
+	for path, pkg := range known {
+		if pkg.GetTypes().Name() != id.Name {
+			continue
+		}
+		// We don't know what this is, so assign it the highest score.
+		score := 0.01 * imports.MaxRelevance
+		c.packageMembers(pkg.GetTypes(), score, &importInfo{
+			importPath: path,
+			name:       pkg.GetTypes().Name(),
+			pkg:        pkg,
+		})
+		if len(c.items) >= unimportedTarget {
+			return nil
+		}
+	}
+
+	ctx, cancel := c.deepCompletionContext()
+	defer cancel()
+	var mu sync.Mutex
+	add := func(pkgExport imports.PackageExport) {
+		mu.Lock()
+		defer mu.Unlock()
+		if _, ok := known[pkgExport.Fix.StmtInfo.ImportPath]; ok {
+			return // We got this one above.
+		}
+
+		// Continue with untyped proposals.
+		pkg := types.NewPackage(pkgExport.Fix.StmtInfo.ImportPath, pkgExport.Fix.IdentName)
+		for _, export := range pkgExport.Exports {
+			score := 0.01 * float64(pkgExport.Fix.Relevance)
+			c.found(candidate{
+				obj:   types.NewVar(0, pkg, export, nil),
+				score: score,
+				imp: &importInfo{
+					importPath: pkgExport.Fix.StmtInfo.ImportPath,
+					name:       pkgExport.Fix.StmtInfo.Name,
+				},
+			})
+		}
+		if len(c.items) >= unimportedTarget {
+			cancel()
+		}
+	}
+	return c.snapshot.View().RunProcessEnvFunc(ctx, func(opts *imports.Options) error {
+		return imports.GetPackageExports(ctx, add, id.Name, c.filename, opts)
+	})
+}
+
+func (c *completer) packageMembers(pkg *types.Package, score float64, imp *importInfo) {
 	scope := pkg.Scope()
 	for _, name := range scope.Names() {
 		obj := scope.Lookup(name)
 		c.found(candidate{
 			obj:         obj,
-			score:       stdScore,
+			score:       score,
 			imp:         imp,
 			addressable: isVar(obj),
 		})

internal/lsp/source/deep_completion.go

@@ -186,7 +186,7 @@ func (c *completer) deepSearch(cand candidate) {
 
 	switch obj := obj.(type) {
 	case *types.PkgName:
-		c.packageMembers(obj.Imported(), cand.imp)
+		c.packageMembers(obj.Imported(), stdScore, cand.imp)
 	default:
 		c.methodsAndFields(obj.Type(), cand.addressable, cand.imp)
 	}