The goal is to permit exercising a single test suite source file with different compiler options producing different sets of diagnostics. While preprocessor directives
can be combined with the existing -verify to accomplish the same goal,
source is often easier to maintain
when it's not cluttered with preprocessor directives or duplicate
passages of code. For example, this patch also rewrites some existing
clang tests to demonstrate the benefit of this feature.
This patch has been sitting for a few weeks without response. I
tried to select appropriate reviewers based on commit logs, but maybe
posting here will help to find reviewers.