internal/lsp: use available type info for unimported completions

Packages that aren't imported in the current file will often have been
used elsewhere, which means that gopls will have their type information
available. Expose loaded packages in the Snapshot, and try to use that
information when possible for unimported packages.

Change-Id: Icb672618a9f9ec31b9796f0c5da56ed3d2b38aa7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/204824
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cache/snapshot.go

@@ -98,6 +98,30 @@ func (s *snapshot) getPackages(uri span.URI, m source.ParseMode) (cphs []source.
 	return cphs
 }
 
+func (s *snapshot) KnownImportPaths() map[string]source.Package {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	results := map[string]source.Package{}
+	for _, cph := range s.packages {
+		cachedPkg, err := cph.cached()
+		if err != nil {
+			continue
+		}
+		for importPath, newPkg := range cachedPkg.imports {
+			if oldPkg, ok := results[string(importPath)]; ok {
+				// Using the same trick as NarrowestPackageHandle, prefer non-variants.
+				if len(newPkg.files) < len(oldPkg.(*pkg).files) {
+					results[string(importPath)] = newPkg
+				}
+			} else {
+				results[string(importPath)] = newPkg
+			}
+		}
+	}
+	return results
+}
+
 func (s *snapshot) getPackage(id packageID, m source.ParseMode) *checkPackageHandle {
 	s.mu.Lock()
 	defer s.mu.Unlock()

internal/lsp/source/completion.go

@@ -587,7 +587,15 @@ func (c *completer) selector(sel *ast.SelectorExpr) error {
 		if err != nil {
 			return err
 		}
+		known := c.snapshot.KnownImportPaths()
 		for _, pkgExport := range pkgExports {
+			// 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(), &pkgExport.Fix.StmtInfo)
+				continue
+			}
+
+			// Otherwise, continue with untyped proposals.
 			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)

internal/lsp/source/view.go

@@ -275,6 +275,10 @@ type Snapshot interface {
 	// CheckPackageHandles returns the CheckPackageHandles for the packages
 	// that this file belongs to.
 	CheckPackageHandles(ctx context.Context, f File) ([]CheckPackageHandle, error)
+
+	// KnownImportPaths returns all the packages loaded in this snapshot,
+	// indexed by their import path.
+	KnownImportPaths() map[string]Package
 }
 
 // File represents a source file of any type.

internal/lsp/testdata/summary.txt.golden

@@ -1,7 +1,7 @@
 -- summary --
 CompletionsCount = 213
 CompletionSnippetCount = 40
-UnimportedCompletionsCount = 2
+UnimportedCompletionsCount = 3
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 7
 RankedCompletionsCount = 8

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

@@ -2,7 +2,9 @@ package unimported
 
 func _() {
 	//@unimported("", bytes, context, cryptoslashrand, time, unsafe, externalpackage)
-	bytes. //@unimported(" /", bytesbuffer)
+	// container/ring is extremely unlikely to be imported by anything, so shouldn't have type information.
+	ring.Ring //@unimported("Ring", ringring)
+	signature.Foo //@unimported("Foo", signaturefoo)
 }
 
 // Create markers for unimported std lib packages. Only for use by this test.
@@ -13,4 +15,6 @@ func _() {
 /* unsafe */ //@item(unsafe, "unsafe", "\"unsafe\"", "package")
 /* pkg */ //@item(externalpackage, "pkg", "\"example.com/extramodule/pkg\"", "package")
 
-/* bytes.Buffer */ //@item(bytesbuffer, "Buffer", "(from \"bytes\")", "var" )
+/* ring.Ring */ //@item(ringring, "Ring", "(from \"container/ring\")", "var")
+
+/* signature.Foo */ //@item(signaturefoo, "Foo", "func(a string, b int) (c bool) (from \"golang.org/x/tools/internal/lsp/signature\")", "func")

internal/lsp/testdata/unimported/unimported_cand_type.go

@@ -1,6 +1,9 @@
 package unimported
 
-import "golang.org/x/tools/internal/lsp/baz"
+import (
+	"golang.org/x/tools/internal/lsp/baz"
+	"golang.org/x/tools/internal/lsp/signature" // provide type information for unimported completions in the other file
+)
 
 func _() {
 	foo.StructFoo{} //@item(litFooStructFoo, "foo.StructFoo{}", "struct{...}", "struct")