pkg/compiler: fix infinite recursion in template instantiation

Currently we replace a template argument and then recurse
into the new type AST to see if there is more to replace.
If the description is buggy and the template argument
contains itself, then we will recurse infintiely trying
to replace it more and more.
Use post-order traversal when replacing template argument to fix this.

1 files changed, 10 insertions, 1 deletions

diff --git a/pkg/ast/walk.go b/pkg/ast/walk.go
index fe9112578..1ec3a8fc6 100644
--- a/pkg/ast/walk.go
+++ b/pkg/ast/walk.go
@@ -4,7 +4,7 @@
 package ast
 
 // Walk calls callback cb for every top-level node in description.
-// Note: it's not recursive. Use Recursive helper for recursive walk.
+// Note: it's not recursive. Use Recursive/PostRecursive helpers for recursive walk.
 func (desc *Description) Walk(cb func(Node)) {
 	for _, n := range desc.Nodes {
 		cb(n)
@@ -20,6 +20,15 @@ func Recursive(cb func(Node)) func(Node) {
 	return rec
 }
 
+func PostRecursive(cb func(Node)) func(Node) {
+	var rec func(Node)
+	rec = func(n Node) {
+		n.Walk(rec)
+		cb(n)
+	}
+	return rec
+}
+
 func (n *NewLine) Walk(cb func(Node)) {}
 func (n *Comment) Walk(cb func(Node)) {}
 func (n *Ident) Walk(cb func(Node))   {}