refactor: minor no-op fixes

- fix typos and mistakes in docstrings, usage message and comments.
- remove 'backup' parameter to rewriteFile

LGTM=sameer
R=sameer
CC=golang-codereviews
https://golang.org/cl/147980043

cmd/gorename/main.go

@@ -64,6 +64,8 @@ Flags:
            (In due course this bug will be fixed by moving certain
            analyses into the type-checker.)
 
+-dryrun    causes the tool to report conflicts but not update any files.
+
 -v         enables verbose logging.
 
 gorename automatically computes the set of packages that might be
@@ -82,7 +84,7 @@ Examples:
 
 % gorename -offset file.go:#123 -to foo
 
-  Rename the object whose identifer is at byte offset 123 within file file.go.
+  Rename the object whose identifier is at byte offset 123 within file file.go.
 
 % gorename -from '(bytes.Buffer).Len' -to Size
 
@@ -91,7 +93,6 @@ Examples:
 ---- TODO ----
 
 Correctness:
-- implement remaining safety checks.
 - handle dot imports correctly
 - document limitations (reflection, 'implements' guesswork).
 - sketch a proof of exhaustiveness.
@@ -113,7 +114,7 @@ Features:
   all local variables of a given type,
   all PkgNames for a given package.
 - emit JSON output for other editors and tools.
-- integration support for editors other than Emacs.
+- integration with editors other than Emacs.
 `
 
 func main() {

refactor/rename/rename.go

@@ -32,10 +32,10 @@ var (
 	// It may even cause gorename to crash.  TODO(adonovan): fix that.
 	Force bool
 
-	// DryRun causes the patch to be displayed but not applied.
+	// DryRun causes the tool to report conflicts but not update any files.
 	DryRun bool
 
-	// ConfictError is returned by Main when it aborts the renaming due to conflicts.
+	// ConflictError is returned by Main when it aborts the renaming due to conflicts.
 	// (It is distinguished because the interesting errors are the conflicts themselves.)
 	ConflictError = errors.New("renaming aborted due to conflicts")
 
@@ -280,7 +280,7 @@ func (r *renamer) update() error {
 							info.Pkg.Path())
 					}
 				}
-				if err := rewriteFile(r.iprog.Fset, f, tokenFile.Name(), tokenFile.Name()+".prename"); err != nil {
+				if err := rewriteFile(r.iprog.Fset, f, tokenFile.Name()); err != nil {
 					fmt.Fprintf(os.Stderr, "Error: %s.\n", err)
 					nerrs++
 				}
@@ -304,7 +304,8 @@ func plural(n int) string {
 	return ""
 }
 
-var rewriteFile = func(fset *token.FileSet, f *ast.File, orig, backup string) (err error) {
+var rewriteFile = func(fset *token.FileSet, f *ast.File, orig string) (err error) {
+	backup := orig + ".prename"
 	// TODO(adonovan): print packages and filenames in a form useful
 	// to editors (so they can reload files).
 	if Verbose {

refactor/rename/rename_test.go

@@ -372,7 +372,7 @@ var _ interface {f()} = C(0)
 }
 
 func TestRewrites(t *testing.T) {
-	defer func(savedRewriteFile func(*token.FileSet, *ast.File, string, string) error) {
+	defer func(savedRewriteFile func(*token.FileSet, *ast.File, string) error) {
 		rewriteFile = savedRewriteFile
 	}(rewriteFile)
 
@@ -654,7 +654,7 @@ func f(z interface{}) {
 		}
 
 		got := make(map[string]string)
-		rewriteFile = func(fset *token.FileSet, f *ast.File, orig, backup string) error {
+		rewriteFile = func(fset *token.FileSet, f *ast.File, orig string) error {
 			var out bytes.Buffer
 			if err := format.Node(&out, fset, f); err != nil {
 				return err