Ensure TreeTransform considers ParmVarDecls as transformed Decls

See PR47804:

TreeTransform uses TransformedLocalDecls as a map of declarations that
have been transformed already. When doing a "TransformDecl", which
happens in the cases of updating a DeclRefExpr's target, the default
implementation simply returns the already transformed declaration.

However, this was not including ParmVarDecls. SO, any use of
TreeTransform that didn't re-implement TransformDecl would NOT properly
update the target of a DeclRefExpr, resulting in odd behavior.

In the case of Typo-recovery, the result was that a lambda that used its
own parameter would cause an error, since it thought that the
ParmVarDecl referenced was a different lambda. Additionally, this caused
a problem in the AST (a declrefexpr into another scope) such that a
future instantiation would cause an assertion.

This patch ensures that the ParmVarDecl transforming process records
into TransformedLocalDecls so that the DeclRefExpr is ALSO updated.

Author: Erich Keane

clang/lib/Sema/TreeTransform.h

@@ -5479,6 +5479,7 @@ ParmVarDecl *TreeTransform<Derived>::TransformFunctionTypeParam(
                                              /* DefArg */ nullptr);
   newParm->setScopeInfo(OldParm->getFunctionScopeDepth(),
                         OldParm->getFunctionScopeIndex() + indexAdjustment);
+  transformedLocalDecl(OldParm, {newParm});
   return newParm;
 }
 

clang/test/SemaCXX/pr47804.cpp

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only %s -verify
+
+template <class InputIt, class Pred>
+bool all_of(InputIt first, Pred p);
+
+template <typename T> void load_test() {
+  // Ensure that this doesn't crash during CorrectDelayedTyposInExpr,
+  // or any other use of TreeTransform that doesn't implement TransformDecl
+  // separately.  Also, this should only error on 'output', not that 'x' is not
+  // captured.
+  // expected-error@+1 {{use of undeclared identifier 'output'}}
+  all_of(output, [](T x) { return x; });
+}
+
+int main() {
+  load_test<int>();
+  return 0;
+}