Merge from mainline (167278:168000).

[official-gcc/graphite-test-results.git] / libgo / go / go / ast / print.go

// 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())
        }
}