[llvm] [llvm][mustache] Fix UB in ASTNode::render() (PR #142249)

[Paul Kirth via llvm-commits]

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@@ -560,68 +566,71 @@ void toMustacheString(const json::Value &Data, raw_ostream &OS) {
   }
 }
 
-void ASTNode::render(const json::Value &Data, raw_ostream &OS) {
-  ParentContext = &Data;
+void ASTNode::render(const json::Value &CurrentCtx, raw_ostream &OS) {
+  // Set the parent context to the incoming context so that we
+  // can walk up the context tree correctly in findContext().
+  ParentContext = &CurrentCtx;
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ilovepi wrote:

So,  think the parent of the node at this point is default/root node. Here we're setting it to the actual parent. I don't think it needs to be reset on the way back up, since they're now fixed in the template/AST. This does make me wonder if there is a better way to set the context/parent relationships than in this recursive routine, though.

https://github.com/llvm/llvm-project/pull/142249