Decl::dump is primarily used for debugging to visualise the current state of a declaration. Usually
Decl::dump just displays the current state of the Decl and doesn't actually change any of its
state, however since commit 457226e02a6e8533eaaa864a3fd7c8eeccd2bf58 the method
actually started loading additional declarations from the ExternalASTSource. This causes that
calling Decl::dump during a debugging session now actually does permanent changes to the
AST and will cause the debugged program run to deviate from the original run.
The change that caused this behaviour is the addition of hasConstexprDestructor
(which is called from the TextNodeDumper) which performs a lookup into the current
CXXRecordDecl to find the destructor. All other similar methods just return their
respective bit in the DefinitionData (which obviously doesn't have such side effects).
This just changes the node printer to emit "unknown_constexpr" in case a CXXRecordDecl
is dumped that could potentially call into the ExternalASTSource instead of the
usually empty string/"constexpr". For CXXRecordDecls that can safely be dumped the
old behaviour is preserved