Merge pull request #53 from hashicorp/add-rewrite

ast: add Rewrite() to rewrite AST

hcl/ast/ast_test.go

@@ -2,6 +2,7 @@ package ast
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/hcl/hcl/token"
@@ -64,3 +65,136 @@ func TestObjectListFilter(t *testing.T) {
 		}
 	}
 }
+
+func TestWalk(t *testing.T) {
+	items := []*ObjectItem{
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"foo"`}},
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"bar"`}},
+			},
+			Val: &LiteralType{Token: token.Token{Type: token.STRING, Text: `"example"`}},
+		},
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"baz"`}},
+			},
+		},
+	}
+
+	node := &ObjectList{Items: items}
+
+	order := []string{
+		"*ast.ObjectList",
+		"*ast.ObjectItem",
+		"*ast.ObjectKey",
+		"*ast.ObjectKey",
+		"*ast.LiteralType",
+		"*ast.ObjectItem",
+		"*ast.ObjectKey",
+	}
+	count := 0
+
+	Walk(node, func(n Node) (Node, bool) {
+		if n == nil {
+			return n, false
+		}
+
+		typeName := reflect.TypeOf(n).String()
+		if order[count] != typeName {
+			t.Errorf("expected '%s' got: '%s'", order[count], typeName)
+		}
+		count++
+		return n, true
+	})
+}
+
+func TestWalkEquality(t *testing.T) {
+	items := []*ObjectItem{
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"foo"`}},
+			},
+		},
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"bar"`}},
+			},
+		},
+	}
+
+	node := &ObjectList{Items: items}
+
+	rewritten := Walk(node, func(n Node) (Node, bool) { return n, true })
+
+	newNode, ok := rewritten.(*ObjectList)
+	if !ok {
+		t.Fatalf("expected Objectlist, got %T", rewritten)
+	}
+
+	if !reflect.DeepEqual(node, newNode) {
+		t.Fatal("rewritten node is not equal to the given node")
+	}
+
+	if len(newNode.Items) != 2 {
+		t.Error("expected newNode length 2, got: %d", len(newNode.Items))
+	}
+
+	expected := []string{
+		`"foo"`,
+		`"bar"`,
+	}
+
+	for i, item := range newNode.Items {
+		if len(item.Keys) != 1 {
+			t.Error("expected keys newNode length 1, got: %d", len(item.Keys))
+		}
+
+		if item.Keys[0].Token.Text != expected[i] {
+			t.Errorf("expected key %s, got %s", expected[i], item.Keys[0].Token.Text)
+		}
+
+		if item.Val != nil {
+			t.Errorf("expected item value should be nil")
+		}
+	}
+}
+
+func TestWalkRewrite(t *testing.T) {
+	items := []*ObjectItem{
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"foo"`}},
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"bar"`}},
+			},
+		},
+		&ObjectItem{
+			Keys: []*ObjectKey{
+				&ObjectKey{Token: token.Token{Type: token.STRING, Text: `"baz"`}},
+			},
+		},
+	}
+
+	node := &ObjectList{Items: items}
+
+	suffix := "_example"
+	node = Walk(node, func(n Node) (Node, bool) {
+		switch i := n.(type) {
+		case *ObjectKey:
+			i.Token.Text = i.Token.Text + suffix
+			n = i
+		}
+		return n, true
+	}).(*ObjectList)
+
+	Walk(node, func(n Node) (Node, bool) {
+		switch i := n.(type) {
+		case *ObjectKey:
+			if !strings.HasSuffix(i.Token.Text, suffix) {
+				t.Errorf("Token '%s' should have suffix: %s", i.Token.Text, suffix)
+			}
+		}
+		return n, true
+	})
+
+}

hcl/ast/walk.go

@@ -2,39 +2,51 @@ package ast
 
 import "fmt"
 
+// WalkFunc describes a function to be called for each node during a Walk. The
+// returned node can be used to rewrite the AST. Walking stops the returned
+// bool is false.
+type WalkFunc func(Node) (Node, bool)
+
 // Walk traverses an AST in depth-first order: It starts by calling fn(node);
-// node must not be nil.  If f returns true, Walk invokes f recursively for
-// each of the non-nil children of node, followed by a call of f(nil).
-func Walk(node Node, fn func(Node) bool) {
-	if !fn(node) {
-		return
+// node must not be nil. If fn returns true, Walk invokes fn recursively for
+// each of the non-nil children of node, followed by a call of fn(nil). The
+// returned node of fn can be used to rewrite the passed node to fn.
+func Walk(node Node, fn WalkFunc) Node {
+	rewritten, ok := fn(node)
+	if !ok {
+		return rewritten
 	}
 
 	switch n := node.(type) {
 	case *File:
-		Walk(n.Node, fn)
+		n.Node = Walk(n.Node, fn)
 	case *ObjectList:
-		for _, item := range n.Items {
-			Walk(item, fn)
+		for i, item := range n.Items {
+			n.Items[i] = Walk(item, fn).(*ObjectItem)
 		}
 	case *ObjectKey:
 		// nothing to do
 	case *ObjectItem:
-		for _, k := range n.Keys {
-			Walk(k, fn)
+		for i, k := range n.Keys {
+			n.Keys[i] = Walk(k, fn).(*ObjectKey)
+		}
+
+		if n.Val != nil {
+			n.Val = Walk(n.Val, fn)
 		}
-		Walk(n.Val, fn)
 	case *LiteralType:
 		// nothing to do
 	case *ListType:
-		for _, l := range n.List {
-			Walk(l, fn)
+		for i, l := range n.List {
+			n.List[i] = Walk(l, fn)
 		}
 	case *ObjectType:
-		Walk(n.List, fn)
+		n.List = Walk(n.List, fn).(*ObjectList)
 	default:
-		fmt.Printf(" unknown type: %T\n", n)
+		// should we panic here?
+		fmt.Printf("unknown type: %T\n", n)
 	}
 
 	fn(nil)
+	return rewritten
 }

hcl/printer/nodes.go

@@ -42,13 +42,13 @@ func (b ByPosition) Less(i, j int) bool { return b[i].Pos().Before(b[j].Pos()) }
 func (p *printer) collectComments(node ast.Node) {
 	// first collect all comments. This is already stored in
 	// ast.File.(comments)
-	ast.Walk(node, func(nn ast.Node) bool {
+	ast.Walk(node, func(nn ast.Node) (ast.Node, bool) {
 		switch t := nn.(type) {
 		case *ast.File:
 			p.comments = t.Comments
-			return false
+			return nn, false
 		}
-		return true
+		return nn, true
 	})
 
 	standaloneComments := make(map[token.Pos]*ast.CommentGroup, 0)
@@ -59,7 +59,7 @@ func (p *printer) collectComments(node ast.Node) {
 	// next remove all lead and line comments from the overall comment map.
 	// This will give us comments which are standalone, comments which are not
 	// assigned to any kind of node.
-	ast.Walk(node, func(nn ast.Node) bool {
+	ast.Walk(node, func(nn ast.Node) (ast.Node, bool) {
 		switch t := nn.(type) {
 		case *ast.LiteralType:
 			if t.LineComment != nil {
@@ -87,7 +87,7 @@ func (p *printer) collectComments(node ast.Node) {
 			}
 		}
 
-		return true
+		return nn, true
 	})
 
 	for _, c := range standaloneComments {

json/parser/flatten.go

@@ -6,11 +6,11 @@ import (
 
 // flattenObjects takes an AST node, walks it, and flattens
 func flattenObjects(node ast.Node) {
-	ast.Walk(node, func(n ast.Node) bool {
+	ast.Walk(node, func(n ast.Node) (ast.Node, bool) {
 		// We only care about lists, because this is what we modify
 		list, ok := n.(*ast.ObjectList)
 		if !ok {
-			return true
+			return n, true
 		}
 
 		// Rebuild the item list
@@ -41,7 +41,7 @@ func flattenObjects(node ast.Node) {
 
 		// Done! Set the original items
 		list.Items = items
-		return true
+		return n, true
 	})
 }