feat: add aliasfix to fix migrated import paths (#6502)

This will assist us in the migration effort and is also a tool our users can use.
The tool is allowlisted to only migrate specific imports, and only if we have
made a configuration change to say the code has been migrated.

internal/aliasfix/README.md

@@ -0,0 +1,14 @@
+# aliasfix
+
+A tool to migrate client library imports from go-genproto to the new stubs
+located in google-cloud-go.
+
+## Usage
+
+Make sure you dependencies for the cloud client library you depend on and
+go-genproto are up to date.
+
+```bash
+go run cloud.google.com/go/aliasfix .
+go mod tidy
+```

internal/aliasfix/go.mod

@@ -0,0 +1,13 @@
+module cloud.google.com/go/aliasfix
+
+go 1.19
+
+require (
+	github.com/google/go-cmp v0.5.8
+	golang.org/x/tools v0.1.12
+)
+
+require (
+	golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 // indirect
+	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f // indirect
+)

internal/aliasfix/go.sum

@@ -0,0 +1,8 @@
+github.com/google/go-cmp v0.5.8 h1:e6P7q2lk1O+qJJb4BtCQXlK8vWEO8V1ZeuEdJNOqZyg=
+github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
+golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=

internal/aliasfix/main.go

@@ -0,0 +1,126 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.18
+// +build go1.18
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"io"
+	"io/fs"
+	"log"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/imports"
+)
+
+var (
+	fset = token.NewFileSet()
+)
+
+func main() {
+	flag.Parse()
+	path := flag.Arg(0)
+	if path == "" {
+		log.Fatalf("expected one argument -- path to the directory needing updates")
+	}
+	if err := processPath(path); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func processPath(path string) error {
+	dir, err := os.Stat(path)
+	if err != nil {
+		return err
+	}
+	if dir.IsDir() {
+		filepath.WalkDir(path, func(path string, d fs.DirEntry, err error) error {
+			if err == nil && !d.IsDir() && strings.HasSuffix(d.Name(), ".go") {
+				err = processFile(path, nil)
+			}
+			if err != nil {
+				return err
+			}
+			return nil
+		})
+	} else {
+		if err := processFile(path, nil); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// processFile checks to see if the given file needs any imports rewritten and
+// does so if needed. Note an io.Writer is injected here for testability.
+func processFile(name string, w io.Writer) error {
+	if w == nil {
+		file, err := os.Open(name)
+		if err != nil {
+			return err
+		}
+		defer file.Close()
+		w = file
+	}
+	f, err := parser.ParseFile(fset, name, nil, parser.ParseComments)
+	if err != nil {
+		return err
+	}
+	var modified bool
+	for _, imp := range f.Imports {
+		importPath, err := strconv.Unquote(imp.Path.Value)
+		if err != nil {
+			return err
+		}
+		if pkg, ok := m[importPath]; ok && pkg.migrated {
+			oldNamespace := importPath[strings.LastIndex(importPath, "/")+1:]
+			newNamespace := pkg.importPath[strings.LastIndex(pkg.importPath, "/")+1:]
+			if imp.Name == nil && oldNamespace != newNamespace {
+				// use old namespace for fewer diffs
+				imp.Name = ast.NewIdent(oldNamespace)
+			} else if imp.Name != nil && imp.Name.Name == newNamespace {
+				// no longer need named import if matching named import
+				imp.Name = nil
+			}
+			imp.EndPos = imp.End()
+			imp.Path.Value = strconv.Quote(pkg.importPath)
+			modified = true
+		}
+	}
+	if modified {
+		var buf bytes.Buffer
+		if err := format.Node(&buf, fset, f); err != nil {
+			return err
+		}
+		b, err := imports.Process(name, buf.Bytes(), nil)
+		if err != nil {
+			return err
+		}
+		if _, err := w.Write(b); err != nil {
+			return err
+		}
+	}
+	return nil
+}

internal/aliasfix/main_test.go

@@ -0,0 +1,106 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.18
+// +build go1.18
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+var updateGoldens bool
+
+func TestMain(m *testing.M) {
+	flag.BoolVar(&updateGoldens, "update-goldens", false, "Update the golden files")
+	flag.Parse()
+	os.Exit(m.Run())
+}
+
+func TestGolden(t *testing.T) {
+	tests := []struct {
+		name     string
+		fileName string
+		modified bool
+	}{
+		{
+			name:     "replace single import",
+			fileName: "input1",
+			modified: true,
+		},
+		{
+			name:     "replace multi-import",
+			fileName: "input2",
+			modified: true,
+		},
+		{
+			name:     "no replaces",
+			fileName: "input3",
+			modified: false,
+		},
+		{
+			name:     "replace single, renamed matching new namespace",
+			fileName: "input4",
+			modified: true,
+		},
+		{
+			name:     "replace multi-import, renamed non-matching",
+			fileName: "input5",
+			modified: true,
+		},
+		{
+			name:     "not-migrated",
+			fileName: "input6",
+			modified: false,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			m["example.com/old/foo"] = pkg{
+				importPath: "example.com/new/foopb",
+				migrated:   tc.modified,
+			}
+			var w bytes.Buffer
+			if updateGoldens {
+				if err := processFile(filepath.Join("testdata", tc.fileName), nil); err != nil {
+					t.Fatal(err)
+				}
+				return
+			}
+			if err := processFile(filepath.Join("testdata", tc.fileName), &w); err != nil {
+				t.Fatal(err)
+			}
+			want, err := os.ReadFile(filepath.Join("testdata", "golden", tc.fileName))
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+			if !tc.modified {
+				if len(w.Bytes()) != 0 {
+					t.Fatalf("source modified:\n%s", w.Bytes())
+				}
+				return
+			}
+			if diff := cmp.Diff(want, w.Bytes()); diff != "" {
+				t.Errorf("bytes mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}