template/parse: add a Walk method to Tree.

R=golang-dev, dsymonds, r
CC=golang-dev, mikesamuel
https://golang.org/cl/4918041

src/pkg/template/parse/Makefile

@@ -10,5 +10,6 @@ GOFILES=\
 	node.go\
 	parse.go\
 	set.go\
+	walk.go\
 
 include ../../../Make.pkg

src/pkg/template/parse/parse_test.go

@@ -7,6 +7,7 @@ package parse
 import (
 	"flag"
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -257,3 +258,129 @@ func TestParse(t *testing.T) {
 		}
 	}
 }
+
+func before(n Node) string {
+	t := ""
+	switch n := n.(type) {
+	case nil:
+		t = "<nil>"
+	case *ActionNode:
+		t = "("
+	case *BoolNode:
+		t = fmt.Sprintf("(%t)", n.True)
+	case *CommandNode:
+		t = "<"
+	case *DotNode:
+		t = "."
+	case *FieldNode:
+		t = "F"
+	case *IdentifierNode:
+		t = fmt.Sprintf("(%s)", n.Ident)
+	case *IfNode:
+		t = "if{"
+	case *ListNode:
+		t = "["
+	case *NumberNode:
+		t = fmt.Sprintf("(%s)", n.Text)
+	case *PipeNode:
+		t = "{"
+	case *RangeNode:
+		t = "range{"
+	case *StringNode:
+		t = fmt.Sprintf("(%q)", n.Text)
+	case *TemplateNode:
+		t = fmt.Sprintf("{template %q", n.Name)
+	case *TextNode:
+		t = fmt.Sprintf("%q", n.Text)
+	case *VariableNode:
+		t = fmt.Sprintf("%q", n.Ident)
+	case *WithNode:
+		t = "with{"
+	default:
+		t = "???"
+	}
+	return t
+}
+
+func after(n Node) string {
+	t := ""
+	switch n := n.(type) {
+	case nil:
+		t = "<nil>"
+	case *ActionNode:
+		t = ")"
+	case *BoolNode:
+	case *CommandNode:
+		t = ">"
+	case *DotNode:
+	case *FieldNode:
+	case *IdentifierNode:
+	case *IfNode:
+		t = "}"
+	case *ListNode:
+		t = "]"
+	case *NumberNode:
+	case *PipeNode:
+		t = "}"
+	case *RangeNode:
+		t = "}"
+	case *StringNode:
+	case *TemplateNode:
+		t = "}"
+	case *TextNode:
+	case *VariableNode:
+	case *WithNode:
+		t = "}"
+	default:
+		t = "???"
+	}
+	return t
+}
+
+// A silly template with lots of pieces to test walking using the before and after functions.
+const walkText = `
+{{range $u, $v  := 3}}
+	{{if .}}
+	{{printf "hi" 3 true 1.2i $u }}
+	{{end}}
+{{else}}
+	{{with .}}
+	{{printf $ | printf}}
+	{{else}}
+	{{template "x"}}
+	{{end}}
+{{end}}`
+
+const walkResult = `
+["\n"range{
+	{["$u"]["$v"]<(3)>}
+	["\n\t"if{
+		{<.>}
+		["\n\t"({<(printf)("hi")(3)(true)(1.2i)["$u"]>})"\n\t"]
+	}"\n"]
+	["\n\t"with{
+		{<.>}
+		["\n\t"({<(printf)["$"]><(printf)>})"\n\t"]
+		["\n\t"{template "x"}"\n\t"]
+	}"\n"]}
+]`
+
+// Use before and after to walk the template and generate a messy but complete print of the template.
+func TestWalk(t *testing.T) {
+	tree, err := New("walk").Parse(walkText, builtins)
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := ""
+	tree.Walk(func(n Node) { s += before(n) }, func(n Node) { s += after(n) })
+	stripSpace := func(r int) int {
+		if r == '\t' || r == '\n' {
+			return -1
+		}
+		return r
+	}
+	expect := strings.Map(stripSpace, walkResult)
+	if s != expect {
+		t.Fatalf("expected\n\t%s\ngot\n\t%s", expect, s)
+	}
+}

src/pkg/template/parse/walk.go

@@ -0,0 +1,89 @@
+// 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 parse
+
+import "fmt"
+
+// Walk walks the parse tree, calling before for each node, then
+// recurring for any non-nil child nodes that node may have, and
+// then calling after.  The before and after functions can be nil.
+func (t *Tree) Walk(before, after func(n Node)) {
+	walk(t.Root, before, after)
+}
+
+func walk(n Node, before, after func(n Node)) {
+	if before != nil {
+		before(n)
+	}
+	switch n := n.(type) {
+	case nil:
+	case *ActionNode:
+		if n.Pipe != nil {
+			walk(n.Pipe, before, after)
+		}
+	case *BoolNode:
+	case *CommandNode:
+		for _, arg := range n.Args {
+			walk(arg, before, after)
+		}
+	case *DotNode:
+	case *FieldNode:
+	case *IdentifierNode:
+	case *IfNode:
+		if n.Pipe != nil {
+			walk(n.Pipe, before, after)
+		}
+		if n.List != nil {
+			walk(n.List, before, after)
+		}
+		if n.ElseList != nil {
+			walk(n.ElseList, before, after)
+		}
+	case *ListNode:
+		for _, node := range n.Nodes {
+			walk(node, before, after)
+		}
+	case *NumberNode:
+	case *PipeNode:
+		for _, decl := range n.Decl {
+			walk(decl, before, after)
+		}
+		for _, cmd := range n.Cmds {
+			walk(cmd, before, after)
+		}
+	case *RangeNode:
+		if n.Pipe != nil {
+			walk(n.Pipe, before, after)
+		}
+		if n.List != nil {
+			walk(n.List, before, after)
+		}
+		if n.ElseList != nil {
+			walk(n.ElseList, before, after)
+		}
+	case *StringNode:
+	case *TemplateNode:
+		if n.Pipe != nil {
+			walk(n.Pipe, before, after)
+		}
+	case *TextNode:
+	case *VariableNode:
+	case *WithNode:
+		if n.Pipe != nil {
+			walk(n.Pipe, before, after)
+		}
+		if n.List != nil {
+			walk(n.List, before, after)
+		}
+		if n.ElseList != nil {
+			walk(n.ElseList, before, after)
+		}
+	default:
+		panic("unknown node of type " + fmt.Sprintf("%T", n))
+	}
+	if after != nil {
+		after(n)
+	}
+}