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.
Erich Keane