refactor/mvpkg: rewrite import comments.

Fixes golang/go#10508.

Change-Id: Id9b0f12e1a81b3b16e167462fd3639a6c6c1e0bb
Reviewed-on: https://go-review.googlesource.com/15267
Reviewed-by: Alan Donovan <adonovan@google.com>

refactor/rename/mvpkg.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/build"
+	"go/token"
 	"log"
 	"os"
 	"os/exec"
@@ -238,6 +239,22 @@ func (m *mover) move() error {
 	}
 	newName := filepath.Base(m.to)
 	for _, f := range pkg.Files {
+		// Update all import comments.
+		for _, cg := range f.Comments {
+			c := cg.List[0]
+			if c.Slash >= f.Name.End() &&
+				sameLine(m.iprog.Fset, c.Slash, f.Name.End()) &&
+				(f.Decls == nil || c.Slash < f.Decls[0].Pos()) {
+				if strings.HasPrefix(c.Text, `// import "`) {
+					c.Text = `// import "` + m.to + `"`
+					break
+				}
+				if strings.HasPrefix(c.Text, `/* import "`) {
+					c.Text = `/* import "` + m.to + `" */`
+					break
+				}
+			}
+		}
 		f.Name.Name = newName // change package decl
 		filesToUpdate[f] = true
 	}
@@ -338,6 +355,11 @@ func (m *mover) move() error {
 	return moveDirectory(m.fromDir, m.toDir)
 }
 
+// sameLine reports whether two positions in the same file are on the same line.
+func sameLine(fset *token.FileSet, x, y token.Pos) bool {
+	return fset.Position(x).Line == fset.Position(y).Line
+}
+
 var moveDirectory = func(from, to string) error {
 	return os.Rename(from, to)
 }

refactor/rename/mvpkg_test.go

@@ -238,6 +238,43 @@ var _ bar.T
 `,
 			},
 		},
+		// package import comments
+		{
+			ctxt: fakeContext(map[string][]string{"foo": {`package foo // import "baz"`}}),
+			from: "foo", to: "bar",
+			want: map[string]string{"/go/src/bar/0.go": `package bar // import "bar"
+`},
+		},
+		{
+			ctxt: fakeContext(map[string][]string{"foo": {`package foo /* import "baz" */`}}),
+			from: "foo", to: "bar",
+			want: map[string]string{"/go/src/bar/0.go": `package bar /* import "bar" */
+`},
+		},
+		{
+			ctxt: fakeContext(map[string][]string{"foo": {`package foo       // import "baz"`}}),
+			from: "foo", to: "bar",
+			want: map[string]string{"/go/src/bar/0.go": `package bar // import "bar"
+`},
+		},
+		{
+			ctxt: fakeContext(map[string][]string{"foo": {`package foo
+// import " this is not an import comment`}}),
+			from: "foo", to: "bar",
+			want: map[string]string{"/go/src/bar/0.go": `package bar
+
+// import " this is not an import comment
+`},
+		},
+		{
+			ctxt: fakeContext(map[string][]string{"foo": {`package foo
+/* import " this is not an import comment */`}}),
+			from: "foo", to: "bar",
+			want: map[string]string{"/go/src/bar/0.go": `package bar
+
+/* import " this is not an import comment */
+`},
+		},
 	}
 
 	for _, test := range tests {