go/ast: fixed bug in NotNilFilter, added test

- fixed a couple of comments
- cleanups after reflect change

R=rsc
CC=golang-dev
https://golang.org/cl/4389041

src/pkg/go/ast/print.go

@@ -26,7 +26,7 @@ func NotNilFilter(_ string, v reflect.Value) bool {
 	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
 		return !v.IsNil()
 	}
-	return false
+	return true
 }
 
 
@@ -80,7 +80,7 @@ type printer struct {
 	output  io.Writer
 	fset    *token.FileSet
 	filter  FieldFilter
-	ptrmap  map[interface{}]int // *reflect.PtrValue -> line number
+	ptrmap  map[interface{}]int // *T -> line number
 	written int                 // number of bytes written to output
 	indent  int                 // current indentation level
 	last    byte                // the last byte processed by Write
@@ -141,6 +141,11 @@ func (p *printer) printf(format string, args ...interface{}) {
 // Implementation note: Print is written for AST nodes but could be
 // used to print arbitrary data structures; such a version should
 // probably be in a different package.
+//
+// Note: This code detects (some) cycles created via pointers but
+// not cycles that are created via slices or maps containing the
+// same slice or map. Code for general data structures probably
+// should catch those as well.
 
 func (p *printer) print(x reflect.Value) {
 	if !NotNilFilter("", x) {
@@ -148,17 +153,17 @@ func (p *printer) print(x reflect.Value) {
 		return
 	}
 
-	switch v := x; v.Kind() {
+	switch x.Kind() {
 	case reflect.Interface:
-		p.print(v.Elem())
+		p.print(x.Elem())
 
 	case reflect.Map:
-		p.printf("%s (len = %d) {\n", x.Type().String(), v.Len())
+		p.printf("%s (len = %d) {\n", x.Type().String(), x.Len())
 		p.indent++
-		for _, key := range v.MapKeys() {
+		for _, key := range x.MapKeys() {
 			p.print(key)
 			p.printf(": ")
-			p.print(v.MapIndex(key))
+			p.print(x.MapIndex(key))
 			p.printf("\n")
 		}
 		p.indent--
@@ -169,24 +174,24 @@ func (p *printer) print(x reflect.Value) {
 		// type-checked ASTs may contain cycles - use ptrmap
 		// to keep track of objects that have been printed
 		// already and print the respective line number instead
-		ptr := v.Interface()
+		ptr := x.Interface()
 		if line, exists := p.ptrmap[ptr]; exists {
 			p.printf("(obj @ %d)", line)
 		} else {
 			p.ptrmap[ptr] = p.line
-			p.print(v.Elem())
+			p.print(x.Elem())
 		}
 
 	case reflect.Slice:
-		if s, ok := v.Interface().([]byte); ok {
+		if s, ok := x.Interface().([]byte); ok {
 			p.printf("%#q", s)
 			return
 		}
-		p.printf("%s (len = %d) {\n", x.Type().String(), v.Len())
+		p.printf("%s (len = %d) {\n", x.Type().String(), x.Len())
 		p.indent++
-		for i, n := 0, v.Len(); i < n; i++ {
+		for i, n := 0, x.Len(); i < n; i++ {
 			p.printf("%d: ", i)
-			p.print(v.Index(i))
+			p.print(x.Index(i))
 			p.printf("\n")
 		}
 		p.indent--
@@ -195,10 +200,10 @@ func (p *printer) print(x reflect.Value) {
 	case reflect.Struct:
 		p.printf("%s {\n", x.Type().String())
 		p.indent++
-		t := v.Type()
+		t := x.Type()
 		for i, n := 0, t.NumField(); i < n; i++ {
 			name := t.Field(i).Name
-			value := v.Field(i)
+			value := x.Field(i)
 			if p.filter == nil || p.filter(name, value) {
 				p.printf("%s: ", name)
 				p.print(value)
@@ -209,11 +214,20 @@ func (p *printer) print(x reflect.Value) {
 		p.printf("}")
 
 	default:
-		value := x.Interface()
+		v := x.Interface()
+		switch v := v.(type) {
+		case string:
+			// print strings in quotes
+			p.printf("%q", v)
+			return
+		case token.Pos:
 			// position values can be printed nicely if we have a file set
-		if pos, ok := value.(token.Pos); ok && p.fset != nil {
+			if p.fset != nil {
-			value = p.fset.Position(pos)
+				p.printf("%s", p.fset.Position(v))
-		}
+				return
-		p.printf("%v", value)
+			}
+		}
+		// default
+		p.printf("%v", v)
 	}
 }

src/pkg/go/ast/print_test.go

@@ -0,0 +1,80 @@
+// Copyright 2011 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 ast
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+
+var tests = []struct {
+	x interface{} // x is printed as s
+	s string
+}{
+	// basic types
+	{nil, "0  nil"},
+	{true, "0  true"},
+	{42, "0  42"},
+	{3.14, "0  3.14"},
+	{1 + 2.718i, "0  (1+2.718i)"},
+	{"foobar", "0  \"foobar\""},
+
+	// maps
+	{map[string]int{"a": 1, "b": 2},
+		`0  map[string] int (len = 2) {
+		1  .  "a": 1
+		2  .  "b": 2
+		3  }`},
+
+	// pointers
+	{new(int), "0  *0"},
+
+	// slices
+	{[]int{1, 2, 3},
+		`0  []int (len = 3) {
+		1  .  0: 1
+		2  .  1: 2
+		3  .  2: 3
+		4  }`},
+
+	// structs
+	{struct{ x, y int }{42, 991},
+		`0  struct { x int; y int } {
+		1  .  x: 42
+		2  .  y: 991
+		3  }`},
+}
+
+
+// Split s into lines, trim whitespace from all lines, and return
+// the concatenated non-empty lines.
+func trim(s string) string {
+	lines := strings.Split(s, "\n", -1)
+	i := 0
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line != "" {
+			lines[i] = line
+			i++
+		}
+	}
+	return strings.Join(lines[0:i], "\n")
+}
+
+
+func TestPrint(t *testing.T) {
+	var buf bytes.Buffer
+	for _, test := range tests {
+		buf.Reset()
+		if _, err := Fprint(&buf, nil, test.x, nil); err != nil {
+			t.Errorf("Fprint failed: %s", err)
+		}
+		if s, ts := trim(buf.String()), trim(test.s); s != ts {
+			t.Errorf("got:\n%s\nexpected:\n%s\n", s, ts)
+		}
+	}
+}