obfuscate literals as part of transformGo (#299)

This is easier to understand, since now the modification of the
*ast.File is all within a single chunk of code. We can also simplify
literals.Obfuscate to work on a single file, as transformGo runs in a
loop.

We also remove the "use receiver" TODOs, since the code is now in a
different package and it can't declare methods on a type here.

internal/literals/literals.go

@@ -33,8 +33,8 @@ func randObfuscator() obfuscator {
 	return obfuscators[randPos]
 }
 
-// Obfuscate replace literals with obfuscated lambda functions
-func Obfuscate(files []*ast.File, info *types.Info, fset *token.FileSet, ignoreObj map[types.Object]bool) []*ast.File {
+// Obfuscate replaces literals with obfuscated anonymous functions.
+func Obfuscate(file *ast.File, info *types.Info, fset *token.FileSet, ignoreObj map[types.Object]bool) *ast.File {
 	pre := func(cursor *astutil.Cursor) bool {
 		switch x := cursor.Node().(type) {
 		case *ast.GenDecl:
@@ -174,10 +174,7 @@ func Obfuscate(files []*ast.File, info *types.Info, fset *token.FileSet, ignoreO
 		return true
 	}
 
-	for i := range files {
-		files[i] = astutil.Apply(files[i], pre, post).(*ast.File)
-	}
-	return files
+	return astutil.Apply(file, pre, post).(*ast.File)
 }
 
 func obfuscateString(data string) *ast.CallExpr {

main.go

@@ -607,11 +607,6 @@ func transformCompile(args []string) ([]string, error) {
 
 	tf.recordReflectArgs(files)
 
-	if opts.GarbleLiterals {
-		// TODO: use transformer here?
-		files = literals.Obfuscate(files, tf.info, fset, tf.ignoreObjects)
-	}
-
 	// Add our temporary dir to the beginning of -trimpath, so that we don't
 	// leak temporary dirs. Needs to be at the beginning, since there may be
 	// shorter prefixes later in the list, such as $PWD if TMPDIR=$PWD/tmp.
@@ -964,7 +959,6 @@ func (tf *transformer) recordReflectArgs(files []*ast.File) {
 
 	visit := func(node ast.Node) bool {
 		if opts.GarbleLiterals {
-			// TODO: use transformer here?
 			literals.RecordUsedAsConstants(node, tf.info, tf.ignoreObjects)
 		}
 
@@ -1014,8 +1008,12 @@ type transformer struct {
 	ignoreObjects map[types.Object]bool
 }
 
-// transformGo garbles the provided Go syntax node.
+// transformGo obfuscates the provided Go syntax file.
 func (tf *transformer) transformGo(file *ast.File) *ast.File {
+	if opts.GarbleLiterals {
+		file = literals.Obfuscate(file, tf.info, fset, tf.ignoreObjects)
+	}
+
 	pre := func(cursor *astutil.Cursor) bool {
 		node, ok := cursor.Node().(*ast.Ident)
 		if !ok {