1 files changed, 217 insertions, 0 deletions
diff --git a/src/pkg/go/ast/print.go b/src/pkg/go/ast/print.go
new file mode 100644
index 000000000..d71490d4a
--- /dev/null
+++ b/src/pkg/go/ast/print.go
@@ -0,0 +1,217 @@
+// 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())
+	}
+}