src/cmd/gofmt/rewrite.go - go - Git at Google

 // Copyright 2009 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 main

 import (
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"go/token"
 	"os"
 	"reflect"
 	"strings"
 	"unicode"
 	"unicode/utf8"
 )

 func initRewrite() {
 	if *rewriteRule == "" {
 		rewrite = nil // disable any previous rewrite
 		return
 	}
 	f := strings.Split(*rewriteRule, "->")
 	if len(f) != 2 {
 		fmt.Fprintf(os.Stderr, "rewrite rule must be of the form 'pattern -> replacement'\n")
 		os.Exit(2)
 	}
 	pattern := parseExpr(f[0], "pattern")
 	replace := parseExpr(f[1], "replacement")
 	rewrite = func(p *ast.File) *ast.File { return rewriteFile(pattern, replace, p) }
 }

 // parseExpr parses s as an expression.
 // It might make sense to expand this to allow statement patterns,
 // but there are problems with preserving formatting and also
 // with what a wildcard for a statement looks like.
 func parseExpr(s, what string) ast.Expr {
 	x, err := parser.ParseExpr(s)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "parsing %s %s at %s\n", what, s, err)
 		os.Exit(2)
 	}
 	return x
 }

 // Keep this function for debugging.
 /*
 func dump(msg string, val reflect.Value) {
 	fmt.Printf("%s:\n", msg)
 	ast.Print(fileSet, val.Interface())
 	fmt.Println()
 }
 */

 // rewriteFile applies the rewrite rule 'pattern -> replace' to an entire file.
 func rewriteFile(pattern, replace ast.Expr, p *ast.File) *ast.File {
 	cmap := ast.NewCommentMap(fileSet, p, p.Comments)
 	m := make(map[string]reflect.Value)
 	pat := reflect.ValueOf(pattern)
 	repl := reflect.ValueOf(replace)

 	var rewriteVal func(val reflect.Value) reflect.Value
 	rewriteVal = func(val reflect.Value) reflect.Value {
 		// don't bother if val is invalid to start with
 		if !val.IsValid() {
 			return reflect.Value{}
 		}
 		val = apply(rewriteVal, val)
 		for k := range m {
 			delete(m, k)
 		}
 		if match(m, pat, val) {
 			val = subst(m, repl, reflect.ValueOf(val.Interface().(ast.Node).Pos()))
 		}
 		return val
 	}

 	r := apply(rewriteVal, reflect.ValueOf(p)).Interface().(*ast.File)
 	r.Comments = cmap.Filter(r).Comments() // recreate comments list
 	return r
 }

 // set is a wrapper for x.Set(y); it protects the caller from panics if x cannot be changed to y.
 func set(x, y reflect.Value) {
 	// don't bother if x cannot be set or y is invalid
 	if !x.CanSet() || !y.IsValid() {
 		return
 	}
 	defer func() {
 		if x := recover(); x != nil {
 			if s, ok := x.(string); ok &&
 				(strings.Contains(s, "type mismatch") || strings.Contains(s, "not assignable")) {
 				// x cannot be set to y - ignore this rewrite
 				return
 			}
 			panic(x)
 		}
 	}()
 	x.Set(y)
 }

 // Values/types for special cases.
 var (
 	objectPtrNil = reflect.ValueOf((*ast.Object)(nil))
 	scopePtrNil  = reflect.ValueOf((*ast.Scope)(nil))

 	identType     = reflect.TypeOf((*ast.Ident)(nil))
 	objectPtrType = reflect.TypeOf((*ast.Object)(nil))
 	positionType  = reflect.TypeOf(token.NoPos)
 	callExprType  = reflect.TypeOf((*ast.CallExpr)(nil))
 	scopePtrType  = reflect.TypeOf((*ast.Scope)(nil))
 )

 // apply replaces each AST field x in val with f(x), returning val.
 // To avoid extra conversions, f operates on the reflect.Value form.
 func apply(f func(reflect.Value) reflect.Value, val reflect.Value) reflect.Value {
 	if !val.IsValid() {
 		return reflect.Value{}
 	}

 	// *ast.Objects introduce cycles and are likely incorrect after
 	// rewrite; don't follow them but replace with nil instead
 	if val.Type() == objectPtrType {
 		return objectPtrNil
 	}

 	// similarly for scopes: they are likely incorrect after a rewrite;
 	// replace them with nil
 	if val.Type() == scopePtrType {
 		return scopePtrNil
 	}

 	switch v := reflect.Indirect(val); v.Kind() {
 	case reflect.Slice:
 		for i := 0; i < v.Len(); i++ {
 			e := v.Index(i)
 			set(e, f(e))
 		}
 	case reflect.Struct:
 		for i := 0; i < v.NumField(); i++ {
 			e := v.Field(i)
 			set(e, f(e))
 		}
 	case reflect.Interface:
 		e := v.Elem()
 		set(v, f(e))
 	}
 	return val
 }

 func isWildcard(s string) bool {
 	rune, size := utf8.DecodeRuneInString(s)
 	return size == len(s) && unicode.IsLower(rune)
 }

 // match reports whether pattern matches val,
 // recording wildcard submatches in m.
 // If m == nil, match checks whether pattern == val.
 func match(m map[string]reflect.Value, pattern, val reflect.Value) bool {
 	// Wildcard matches any expression. If it appears multiple
 	// times in the pattern, it must match the same expression
 	// each time.
 	if m != nil && pattern.IsValid() && pattern.Type() == identType {
 		name := pattern.Interface().(*ast.Ident).Name
 		if isWildcard(name) && val.IsValid() {
 			// wildcards only match valid (non-nil) expressions.
 			if _, ok := val.Interface().(ast.Expr); ok && !val.IsNil() {
 				if old, ok := m[name]; ok {
 					return match(nil, old, val)
 				}
 				m[name] = val
 				return true
 			}
 		}
 	}

 	// Otherwise, pattern and val must match recursively.
 	if !pattern.IsValid() || !val.IsValid() {
 		return !pattern.IsValid() && !val.IsValid()
 	}
 	if pattern.Type() != val.Type() {
 		return false
 	}

 	// Special cases.
 	switch pattern.Type() {
 	case identType:
 		// For identifiers, only the names need to match
 		// (and none of the other *ast.Object information).
 		// This is a common case, handle it all here instead
 		// of recursing down any further via reflection.
 		p := pattern.Interface().(*ast.Ident)
 		v := val.Interface().(*ast.Ident)
 		return p == nil && v == nil || p != nil && v != nil && p.Name == v.Name
 	case objectPtrType, positionType:
 		// object pointers and token positions always match
 		return true
 	case callExprType:
 		// For calls, the Ellipsis fields (token.Position) must
 		// match since that is how f(x) and f(x...) are different.
 		// Check them here but fall through for the remaining fields.
 		p := pattern.Interface().(*ast.CallExpr)
 		v := val.Interface().(*ast.CallExpr)
 		if p.Ellipsis.IsValid() != v.Ellipsis.IsValid() {
 			return false
 		}
 	}

 	p := reflect.Indirect(pattern)
 	v := reflect.Indirect(val)
 	if !p.IsValid() || !v.IsValid() {
 		return !p.IsValid() && !v.IsValid()
 	}

 	switch p.Kind() {
 	case reflect.Slice:
 		if p.Len() != v.Len() {
 			return false
 		}
 		for i := 0; i < p.Len(); i++ {
 			if !match(m, p.Index(i), v.Index(i)) {
 				return false
 			}
 		}
 		return true

 	case reflect.Struct:
 		for i := 0; i < p.NumField(); i++ {
 			if !match(m, p.Field(i), v.Field(i)) {
 				return false
 			}
 		}
 		return true

 	case reflect.Interface:
 		return match(m, p.Elem(), v.Elem())
 	}

 	// Handle token integers, etc.
 	return p.Interface() == v.Interface()
 }

 // subst returns a copy of pattern with values from m substituted in place
 // of wildcards and pos used as the position of tokens from the pattern.
 // if m == nil, subst returns a copy of pattern and doesn't change the line
 // number information.
 func subst(m map[string]reflect.Value, pattern reflect.Value, pos reflect.Value) reflect.Value {
 	if !pattern.IsValid() {
 		return reflect.Value{}
 	}

 	// Wildcard gets replaced with map value.
 	if m != nil && pattern.Type() == identType {
 		name := pattern.Interface().(*ast.Ident).Name
 		if isWildcard(name) {
 			if old, ok := m[name]; ok {
 				return subst(nil, old, reflect.Value{})
 			}
 		}
 	}

 	if pos.IsValid() && pattern.Type() == positionType {
 		// use new position only if old position was valid in the first place
 		if old := pattern.Interface().(token.Pos); !old.IsValid() {
 			return pattern
 		}
 		return pos
 	}

 	// Otherwise copy.
 	switch p := pattern; p.Kind() {
 	case reflect.Slice:
 		if p.IsNil() {
 			// Do not turn nil slices into empty slices. go/ast
 			// guarantees that certain lists will be nil if not
 			// populated.
 			return reflect.Zero(p.Type())
 		}
 		v := reflect.MakeSlice(p.Type(), p.Len(), p.Len())
 		for i := 0; i < p.Len(); i++ {
 			v.Index(i).Set(subst(m, p.Index(i), pos))
 		}
 		return v

 	case reflect.Struct:
 		v := reflect.New(p.Type()).Elem()
 		for i := 0; i < p.NumField(); i++ {
 			v.Field(i).Set(subst(m, p.Field(i), pos))
 		}
 		return v

 	case reflect.Ptr:
 		v := reflect.New(p.Type()).Elem()
 		if elem := p.Elem(); elem.IsValid() {
 			v.Set(subst(m, elem, pos).Addr())
 		}
 		return v

 	case reflect.Interface:
 		v := reflect.New(p.Type()).Elem()
 		if elem := p.Elem(); elem.IsValid() {
 			v.Set(subst(m, elem, pos))
 		}
 		return v
 	}

 	return pattern
 }
	// Copyright 2009 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 main

	import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"os"
	"reflect"
	"strings"
	"unicode"
	"unicode/utf8"
	)

	func initRewrite() {
	if *rewriteRule == "" {
	rewrite = nil // disable any previous rewrite
	return
	}
	f := strings.Split(*rewriteRule, "->")
	if len(f) != 2 {
	fmt.Fprintf(os.Stderr, "rewrite rule must be of the form 'pattern -> replacement'\n")
	os.Exit(2)
	}
	pattern := parseExpr(f[0], "pattern")
	replace := parseExpr(f[1], "replacement")
	rewrite = func(p ast.File) ast.File { return rewriteFile(pattern, replace, p) }
	}

	// parseExpr parses s as an expression.
	// It might make sense to expand this to allow statement patterns,
	// but there are problems with preserving formatting and also
	// with what a wildcard for a statement looks like.
	func parseExpr(s, what string) ast.Expr {
	x, err := parser.ParseExpr(s)
	if err != nil {
	fmt.Fprintf(os.Stderr, "parsing %s %s at %s\n", what, s, err)
	os.Exit(2)
	}
	return x
	}

	// Keep this function for debugging.
	/*
	func dump(msg string, val reflect.Value) {
	fmt.Printf("%s:\n", msg)
	ast.Print(fileSet, val.Interface())
	fmt.Println()
	}
	*/

	// rewriteFile applies the rewrite rule 'pattern -> replace' to an entire file.
	func rewriteFile(pattern, replace ast.Expr, p ast.File) ast.File {
	cmap := ast.NewCommentMap(fileSet, p, p.Comments)
	m := make(map[string]reflect.Value)
	pat := reflect.ValueOf(pattern)
	repl := reflect.ValueOf(replace)

	var rewriteVal func(val reflect.Value) reflect.Value
	rewriteVal = func(val reflect.Value) reflect.Value {
	// don't bother if val is invalid to start with
	if !val.IsValid() {
	return reflect.Value{}
	}
	val = apply(rewriteVal, val)
	for k := range m {
	delete(m, k)
	}
	if match(m, pat, val) {
	val = subst(m, repl, reflect.ValueOf(val.Interface().(ast.Node).Pos()))
	}
	return val
	}

	r := apply(rewriteVal, reflect.ValueOf(p)).Interface().(*ast.File)
	r.Comments = cmap.Filter(r).Comments() // recreate comments list
	return r
	}

	// set is a wrapper for x.Set(y); it protects the caller from panics if x cannot be changed to y.
	func set(x, y reflect.Value) {
	// don't bother if x cannot be set or y is invalid
	if !x.CanSet() \|\| !y.IsValid() {
	return
	}
	defer func() {
	if x := recover(); x != nil {
	if s, ok := x.(string); ok &&
	(strings.Contains(s, "type mismatch") \|\| strings.Contains(s, "not assignable")) {
	// x cannot be set to y - ignore this rewrite
	return
	}
	panic(x)
	}
	}()
	x.Set(y)
	}

	// Values/types for special cases.
	var (
	objectPtrNil = reflect.ValueOf((*ast.Object)(nil))
	scopePtrNil = reflect.ValueOf((*ast.Scope)(nil))

	identType = reflect.TypeOf((*ast.Ident)(nil))
	objectPtrType = reflect.TypeOf((*ast.Object)(nil))
	positionType = reflect.TypeOf(token.NoPos)
	callExprType = reflect.TypeOf((*ast.CallExpr)(nil))
	scopePtrType = reflect.TypeOf((*ast.Scope)(nil))
	)

	// apply replaces each AST field x in val with f(x), returning val.
	// To avoid extra conversions, f operates on the reflect.Value form.
	func apply(f func(reflect.Value) reflect.Value, val reflect.Value) reflect.Value {
	if !val.IsValid() {
	return reflect.Value{}
	}

	// *ast.Objects introduce cycles and are likely incorrect after
	// rewrite; don't follow them but replace with nil instead
	if val.Type() == objectPtrType {
	return objectPtrNil
	}

	// similarly for scopes: they are likely incorrect after a rewrite;
	// replace them with nil
	if val.Type() == scopePtrType {
	return scopePtrNil
	}

	switch v := reflect.Indirect(val); v.Kind() {
	case reflect.Slice:
	for i := 0; i < v.Len(); i++ {
	e := v.Index(i)
	set(e, f(e))
	}
	case reflect.Struct:
	for i := 0; i < v.NumField(); i++ {
	e := v.Field(i)
	set(e, f(e))
	}
	case reflect.Interface:
	e := v.Elem()
	set(v, f(e))
	}
	return val
	}

	func isWildcard(s string) bool {
	rune, size := utf8.DecodeRuneInString(s)
	return size == len(s) && unicode.IsLower(rune)
	}

	// match reports whether pattern matches val,
	// recording wildcard submatches in m.
	// If m == nil, match checks whether pattern == val.
	func match(m map[string]reflect.Value, pattern, val reflect.Value) bool {
	// Wildcard matches any expression. If it appears multiple
	// times in the pattern, it must match the same expression
	// each time.
	if m != nil && pattern.IsValid() && pattern.Type() == identType {
	name := pattern.Interface().(*ast.Ident).Name
	if isWildcard(name) && val.IsValid() {
	// wildcards only match valid (non-nil) expressions.
	if _, ok := val.Interface().(ast.Expr); ok && !val.IsNil() {
	if old, ok := m[name]; ok {
	return match(nil, old, val)
	}
	m[name] = val
	return true
	}
	}
	}

	// Otherwise, pattern and val must match recursively.
	if !pattern.IsValid() \|\| !val.IsValid() {
	return !pattern.IsValid() && !val.IsValid()
	}
	if pattern.Type() != val.Type() {
	return false
	}

	// Special cases.
	switch pattern.Type() {
	case identType:
	// For identifiers, only the names need to match
	// (and none of the other *ast.Object information).
	// This is a common case, handle it all here instead
	// of recursing down any further via reflection.
	p := pattern.Interface().(*ast.Ident)
	v := val.Interface().(*ast.Ident)
	return p == nil && v == nil \|\| p != nil && v != nil && p.Name == v.Name
	case objectPtrType, positionType:
	// object pointers and token positions always match
	return true
	case callExprType:
	// For calls, the Ellipsis fields (token.Position) must
	// match since that is how f(x) and f(x...) are different.
	// Check them here but fall through for the remaining fields.
	p := pattern.Interface().(*ast.CallExpr)
	v := val.Interface().(*ast.CallExpr)
	if p.Ellipsis.IsValid() != v.Ellipsis.IsValid() {
	return false
	}
	}

	p := reflect.Indirect(pattern)
	v := reflect.Indirect(val)
	if !p.IsValid() \|\| !v.IsValid() {
	return !p.IsValid() && !v.IsValid()
	}

	switch p.Kind() {
	case reflect.Slice:
	if p.Len() != v.Len() {
	return false
	}
	for i := 0; i < p.Len(); i++ {
	if !match(m, p.Index(i), v.Index(i)) {
	return false
	}
	}
	return true

	case reflect.Struct:
	for i := 0; i < p.NumField(); i++ {
	if !match(m, p.Field(i), v.Field(i)) {
	return false
	}
	}
	return true

	case reflect.Interface:
	return match(m, p.Elem(), v.Elem())
	}

	// Handle token integers, etc.
	return p.Interface() == v.Interface()
	}

	// subst returns a copy of pattern with values from m substituted in place
	// of wildcards and pos used as the position of tokens from the pattern.
	// if m == nil, subst returns a copy of pattern and doesn't change the line
	// number information.
	func subst(m map[string]reflect.Value, pattern reflect.Value, pos reflect.Value) reflect.Value {
	if !pattern.IsValid() {
	return reflect.Value{}
	}

	// Wildcard gets replaced with map value.
	if m != nil && pattern.Type() == identType {
	name := pattern.Interface().(*ast.Ident).Name
	if isWildcard(name) {
	if old, ok := m[name]; ok {
	return subst(nil, old, reflect.Value{})
	}
	}
	}

	if pos.IsValid() && pattern.Type() == positionType {
	// use new position only if old position was valid in the first place
	if old := pattern.Interface().(token.Pos); !old.IsValid() {
	return pattern
	}
	return pos
	}

	// Otherwise copy.
	switch p := pattern; p.Kind() {
	case reflect.Slice:
	if p.IsNil() {
	// Do not turn nil slices into empty slices. go/ast
	// guarantees that certain lists will be nil if not
	// populated.
	return reflect.Zero(p.Type())
	}
	v := reflect.MakeSlice(p.Type(), p.Len(), p.Len())
	for i := 0; i < p.Len(); i++ {
	v.Index(i).Set(subst(m, p.Index(i), pos))
	}
	return v

	case reflect.Struct:
	v := reflect.New(p.Type()).Elem()
	for i := 0; i < p.NumField(); i++ {
	v.Field(i).Set(subst(m, p.Field(i), pos))
	}
	return v

	case reflect.Ptr:
	v := reflect.New(p.Type()).Elem()
	if elem := p.Elem(); elem.IsValid() {
	v.Set(subst(m, elem, pos).Addr())
	}
	return v

	case reflect.Interface:
	v := reflect.New(p.Type()).Elem()
	if elem := p.Elem(); elem.IsValid() {
	v.Set(subst(m, elem, pos))
	}
	return v
	}

	return pattern
	}