[clang] [Clang] Add default arguments to the parameter mapping (PR #192071)

[Timm Baeder via cfe-commits]

================
@@ -2105,6 +2105,25 @@ void SubstituteParameterMappings::buildParameterMapping(
       SemaRef.MarkUsedTemplateParameters(Args->arguments(),
                                          /*Depth=*/0, OccurringIndices);
   }
+
+  // If a parameter is only referenced in a default template argument,
+  // we need to add it to the mapping explicitly.
+  {
+    llvm::SmallVector<TemplateArgument> DefaultArgs;
+    for (unsigned I = TemplateParams->getMinRequiredArguments();
+         I < TemplateParams->size(); I++) {
----------------
tbaederr wrote:

```suggestion
         I < TemplateParams->size(); ++I) {
```

https://github.com/llvm/llvm-project/pull/192071