2 files changed, 209 insertions, 0 deletions
diff --git a/src/go/importer/importer.go b/src/go/importer/importer.go
new file mode 100644
index 0000000..23118d3
--- /dev/null
+++ b/src/go/importer/importer.go
@@ -0,0 +1,122 @@
+// Copyright 2015 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 importer provides access to export data importers.
+package importer
+
+import (
+	"go/build"
+	"go/internal/gccgoimporter"
+	"go/internal/gcimporter"
+	"go/internal/srcimporter"
+	"go/token"
+	"go/types"
+	"io"
+	"runtime"
+)
+
+// A Lookup function returns a reader to access package data for
+// a given import path, or an error if no matching package is found.
+type Lookup func(path string) (io.ReadCloser, error)
+
+// ForCompiler returns an Importer for importing from installed packages
+// for the compilers "gc" and "gccgo", or for importing directly
+// from the source if the compiler argument is "source". In this
+// latter case, importing may fail under circumstances where the
+// exported API is not entirely defined in pure Go source code
+// (if the package API depends on cgo-defined entities, the type
+// checker won't have access to those).
+//
+// The lookup function is called each time the resulting importer needs
+// to resolve an import path. In this mode the importer can only be
+// invoked with canonical import paths (not relative or absolute ones);
+// it is assumed that the translation to canonical import paths is being
+// done by the client of the importer.
+//
+// A lookup function must be provided for correct module-aware operation.
+// Deprecated: If lookup is nil, for backwards-compatibility, the importer
+// will attempt to resolve imports in the $GOPATH workspace.
+func ForCompiler(fset *token.FileSet, compiler string, lookup Lookup) types.Importer {
+	switch compiler {
+	case "gc":
+		return &gcimports{
+			fset:     fset,
+			packages: make(map[string]*types.Package),
+			lookup:   lookup,
+		}
+
+	case "gccgo":
+		var inst gccgoimporter.GccgoInstallation
+		if err := inst.InitFromDriver("gccgo"); err != nil {
+			return nil
+		}
+		return &gccgoimports{
+			packages: make(map[string]*types.Package),
+			importer: inst.GetImporter(nil, nil),
+			lookup:   lookup,
+		}
+
+	case "source":
+		if lookup != nil {
+			panic("source importer for custom import path lookup not supported (issue #13847).")
+		}
+
+		return srcimporter.New(&build.Default, fset, make(map[string]*types.Package))
+	}
+
+	// compiler not supported
+	return nil
+}
+
+// For calls ForCompiler with a new FileSet.
+//
+// Deprecated: Use ForCompiler, which populates a FileSet
+// with the positions of objects created by the importer.
+func For(compiler string, lookup Lookup) types.Importer {
+	return ForCompiler(token.NewFileSet(), compiler, lookup)
+}
+
+// Default returns an Importer for the compiler that built the running binary.
+// If available, the result implements types.ImporterFrom.
+func Default() types.Importer {
+	return For(runtime.Compiler, nil)
+}
+
+// gc importer
+
+type gcimports struct {
+	fset     *token.FileSet
+	packages map[string]*types.Package
+	lookup   Lookup
+}
+
+func (m *gcimports) Import(path string) (*types.Package, error) {
+	return m.ImportFrom(path, "" /* no vendoring */, 0)
+}
+
+func (m *gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
+	if mode != 0 {
+		panic("mode must be 0")
+	}
+	return gcimporter.Import(m.fset, m.packages, path, srcDir, m.lookup)
+}
+
+// gccgo importer
+
+type gccgoimports struct {
+	packages map[string]*types.Package
+	importer gccgoimporter.Importer
+	lookup   Lookup
+}
+
+func (m *gccgoimports) Import(path string) (*types.Package, error) {
+	return m.ImportFrom(path, "" /* no vendoring */, 0)
+}
+
+func (m *gccgoimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
+	if mode != 0 {
+		panic("mode must be 0")
+	}
+	return m.importer(m.packages, path, srcDir, m.lookup)
+}
diff --git a/src/go/importer/importer_test.go b/src/go/importer/importer_test.go
new file mode 100644
index 0000000..0f5121d
--- /dev/null
+++ b/src/go/importer/importer_test.go
@@ -0,0 +1,87 @@
+// Copyright 2017 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 importer
+
+import (
+	"go/token"
+	"internal/testenv"
+	"io"
+	"os"
+	"os/exec"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestForCompiler(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	const thePackage = "math/big"
+	out, err := exec.Command(testenv.GoToolPath(t), "list", "-f={{context.Compiler}}:{{.Target}}", thePackage).CombinedOutput()
+	if err != nil {
+		t.Fatalf("go list %s: %v\n%s", thePackage, err, out)
+	}
+	target := strings.TrimSpace(string(out))
+	i := strings.Index(target, ":")
+	compiler, target := target[:i], target[i+1:]
+	if !strings.HasSuffix(target, ".a") {
+		t.Fatalf("unexpected package %s target %q (not *.a)", thePackage, target)
+	}
+
+	if compiler == "gccgo" {
+		t.Skip("golang.org/issue/22500")
+	}
+
+	fset := token.NewFileSet()
+
+	t.Run("LookupDefault", func(t *testing.T) {
+		imp := ForCompiler(fset, compiler, nil)
+		pkg, err := imp.Import(thePackage)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if pkg.Path() != thePackage {
+			t.Fatalf("Path() = %q, want %q", pkg.Path(), thePackage)
+		}
+
+		// Check that the fileset positions are accurate.
+		// https://github.com/golang/go#28995
+		mathBigInt := pkg.Scope().Lookup("Int")
+		posn := fset.Position(mathBigInt.Pos()) // "$GOROOT/src/math/big/int.go:25:1"
+		filename := strings.Replace(posn.Filename, "$GOROOT", runtime.GOROOT(), 1)
+		data, err := os.ReadFile(filename)
+		if err != nil {
+			t.Fatalf("can't read file containing declaration of math/big.Int: %v", err)
+		}
+		lines := strings.Split(string(data), "\n")
+		if posn.Line > len(lines) || !strings.HasPrefix(lines[posn.Line-1], "type Int") {
+			t.Fatalf("Object %v position %s does not contain its declaration",
+				mathBigInt, posn)
+		}
+	})
+
+	t.Run("LookupCustom", func(t *testing.T) {
+		lookup := func(path string) (io.ReadCloser, error) {
+			if path != "math/bigger" {
+				t.Fatalf("lookup called with unexpected path %q", path)
+			}
+			f, err := os.Open(target)
+			if err != nil {
+				t.Fatal(err)
+			}
+			return f, nil
+		}
+		imp := ForCompiler(fset, compiler, lookup)
+		pkg, err := imp.Import("math/bigger")
+		if err != nil {
+			t.Fatal(err)
+		}
+		// Even though we open math/big.a, the import request was for math/bigger
+		// and that should be recorded in pkg.Path(), at least for the gc toolchain.
+		if pkg.Path() != "math/bigger" {
+			t.Fatalf("Path() = %q, want %q", pkg.Path(), "math/bigger")
+		}
+	})
+}