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// Copyright 2010 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.
// This file contains printing suppport for ASTs.
package ast
import (
"fmt"
"go/token"
"io"
"os"
"reflect"
)
// A FieldFilter may be provided to Fprint to control the output.
type FieldFilter func(name string, value reflect.Value) bool
// NotNilFilter returns true for field values that are not nil;
// it returns false otherwise.
func NotNilFilter(_ string, value reflect.Value) bool {
v, ok := value.(interface {
IsNil() bool
})
return !ok || !v.IsNil()
}
// Fprint prints the (sub-)tree starting at AST node x to w.
//
// A non-nil FieldFilter f may be provided to control the output:
// struct fields for which f(fieldname, fieldvalue) is true are
// are printed; all others are filtered from the output.
//
func Fprint(w io.Writer, x interface{}, f FieldFilter) (n int, err os.Error) {
// setup printer
p := printer{
output: w,
filter: f,
ptrmap: make(map[interface{}]int),
last: '\n', // force printing of line number on first line
}
// install error handler
defer func() {
n = p.written
if e := recover(); e != nil {
err = e.(localError).err // re-panics if it's not a localError
}
}()
// print x
if x == nil {
p.printf("nil\n")
return
}
p.print(reflect.NewValue(x))
p.printf("\n")
return
}
// Print prints x to standard output, skipping nil fields.
// Print(x) is the same as Fprint(os.Stdout, x, NotNilFilter).
func Print(x interface{}) (int, os.Error) {
return Fprint(os.Stdout, x, NotNilFilter)
}
type printer struct {
output io.Writer
filter FieldFilter
ptrmap map[interface{}]int // *reflect.PtrValue -> line number
written int // number of bytes written to output
indent int // current indentation level
last byte // the last byte processed by Write
line int // current line number
}
var indent = []byte(". ")
func (p *printer) Write(data []byte) (n int, err os.Error) {
var m int
for i, b := range data {
// invariant: data[0:n] has been written
if b == '\n' {
m, err = p.output.Write(data[n : i+1])
n += m
if err != nil {
return
}
p.line++
} else if p.last == '\n' {
_, err = fmt.Fprintf(p.output, "%6d ", p.line)
if err != nil {
return
}
for j := p.indent; j > 0; j-- {
_, err = p.output.Write(indent)
if err != nil {
return
}
}
}
p.last = b
}
m, err = p.output.Write(data[n:])
n += m
return
}
// localError wraps locally caught os.Errors so we can distinguish
// them from genuine panics which we don't want to return as errors.
type localError struct {
err os.Error
}
// printf is a convenience wrapper that takes care of print errors.
func (p *printer) printf(format string, args ...interface{}) {
n, err := fmt.Fprintf(p, format, args...)
p.written += n
if err != nil {
panic(localError{err})
}
}
// 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.
func (p *printer) print(x reflect.Value) {
// Note: This test is only needed because AST nodes
// embed a token.Position, and thus all of them
// understand the String() method (but it only
// applies to the Position field).
// TODO: Should reconsider this AST design decision.
if pos, ok := x.Interface().(token.Position); ok {
p.printf("%s", pos)
return
}
if !NotNilFilter("", x) {
p.printf("nil")
return
}
switch v := x.(type) {
case *reflect.InterfaceValue:
p.print(v.Elem())
case *reflect.MapValue:
p.printf("%s (len = %d) {\n", x.Type().String(), v.Len())
p.indent++
for _, key := range v.Keys() {
p.print(key)
p.printf(": ")
p.print(v.Elem(key))
}
p.indent--
p.printf("}")
case *reflect.PtrValue:
p.printf("*")
// 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()
if line, exists := p.ptrmap[ptr]; exists {
p.printf("(obj @ %d)", line)
} else {
p.ptrmap[ptr] = p.line
p.print(v.Elem())
}
case *reflect.SliceValue:
if s, ok := v.Interface().([]byte); ok {
p.printf("%#q", s)
return
}
p.printf("%s (len = %d) {\n", x.Type().String(), v.Len())
p.indent++
for i, n := 0, v.Len(); i < n; i++ {
p.printf("%d: ", i)
p.print(v.Elem(i))
p.printf("\n")
}
p.indent--
p.printf("}")
case *reflect.StructValue:
p.printf("%s {\n", x.Type().String())
p.indent++
t := v.Type().(*reflect.StructType)
for i, n := 0, t.NumField(); i < n; i++ {
name := t.Field(i).Name
value := v.Field(i)
if p.filter == nil || p.filter(name, value) {
p.printf("%s: ", name)
p.print(value)
p.printf("\n")
}
}
p.indent--
p.printf("}")
default:
p.printf("%v", x.Interface())
}
}
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