go/internal/gcimporter: add test of export/import on std

This test ensures that all std and x/tools packages can
be re-typechecked using export data.

Change-Id: I189a8138d74cb38f69dfb51c613849e43b316322
Reviewed-on: https://go-review.googlesource.com/c/tools/+/445096
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

go/internal/gcimporter/stdlib_test.go

@@ -0,0 +1,82 @@
+// Copyright 2022 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 gcimporter_test
+
+import (
+	"bytes"
+	"fmt"
+	"go/token"
+	"go/types"
+	"testing"
+	"unsafe"
+
+	"golang.org/x/tools/go/gcexportdata"
+	"golang.org/x/tools/go/packages"
+	"golang.org/x/tools/internal/testenv"
+)
+
+// TestStdlib ensures that all packages in std and x/tools can be
+// type-checked using export data. Takes around 3s.
+func TestStdlib(t *testing.T) {
+	testenv.NeedsGoPackages(t)
+
+	// gcexportdata.Read rapidly consumes FileSet address space,
+	// so disable the test on 32-bit machines.
+	// (We could use a fresh FileSet per type-check, but that
+	// would require us to re-parse the source using it.)
+	if unsafe.Sizeof(token.NoPos) < 8 {
+		t.Skip("skipping test on 32-bit machine")
+	}
+
+	// Load, parse and type-check the standard library and x/tools.
+	cfg := &packages.Config{Mode: packages.LoadAllSyntax}
+	pkgs, err := packages.Load(cfg, "std", "golang.org/x/tools/...")
+	if err != nil {
+		t.Fatalf("failed to load/parse/type-check: %v", err)
+	}
+	if packages.PrintErrors(pkgs) > 0 {
+		t.Fatal("there were errors during loading")
+	}
+	if len(pkgs) < 240 {
+		t.Errorf("too few packages (%d) were loaded", len(pkgs))
+	}
+
+	export := make(map[string][]byte) // keys are package IDs
+
+	// Re-type check them all in post-order, using export data.
+	packages.Visit(pkgs, nil, func(pkg *packages.Package) {
+		packages := make(map[string]*types.Package) // keys are package paths
+		cfg := &types.Config{
+			Error: func(e error) {
+				t.Errorf("type error: %v", e)
+			},
+			Importer: importerFunc(func(importPath string) (*types.Package, error) {
+				// Resolve import path to (vendored?) package path.
+				imported := pkg.Imports[importPath]
+
+				if imported.PkgPath == "unsafe" {
+					return types.Unsafe, nil // unsafe has no exportdata
+				}
+
+				data, ok := export[imported.ID]
+				if !ok {
+					return nil, fmt.Errorf("missing export data for %s", importPath)
+				}
+				return gcexportdata.Read(bytes.NewReader(data), pkg.Fset, packages, imported.PkgPath)
+			}),
+		}
+
+		// Re-typecheck the syntax and save the export data in the map.
+		newPkg := types.NewPackage(pkg.PkgPath, pkg.Name)
+		check := types.NewChecker(cfg, pkg.Fset, newPkg, nil)
+		check.Files(pkg.Syntax)
+
+		var out bytes.Buffer
+		if err := gcexportdata.Write(&out, pkg.Fset, newPkg); err != nil {
+			t.Fatalf("internal error writing export data: %v", err)
+		}
+		export[pkg.ID] = out.Bytes()
+	})
+}