[cfe-dev] Tests for C++0x Confusion

[Sebastian Redl]

On 19.12.2010 20:15, Michael Price wrote:
> I'm a bit confused about the organization of the C++0x tests.  Under 
> the clang/test directory I see the following seemingly C++0x related 
> directories:
>
> Lexer/
> SemaCXX/
> CodeGenCXX/
> Fixit/
> Lexer/
> PCH/
> Parser/
> Preprocessor/
> SemaTemplate/
> (this is the one that confuses me the most, are thing organized by 
> compiler arch, or by language/version?) CXX/
>
> Am I in the dark on how these thing are organized?
>
You're mostly looking at a historical artifact.

When Clang started as a C/Obj-C compiler (C++ was meant to be in there, 
but wasn't really planned for), it had some test directories: 
Preprocessor, Lexer, Parser, Sema, and CodeGen. This made sense, because 
in C those components are pretty much completely distinct. We had the 
MinimalAction, which just provided enough semantic analysis to make C 
parsing work, so you could run the C parser without Sema. When ObjC 
became a reality, only Sema and CodeGen received a significant number of 
new tests, so SemaObjC and CodeGenObjC were added.
When C++ support came into being, SemaCXX and CodeGenCXX were added 
along the same lines of reasoning. Templates were so complex and 
demanded so many tests that SemaTemplate was split out of SemaCXX.
However, the organization as it is makes a lot less sense for C++ than 
for C. For C++, there's no real minimal analysis that you can use for 
parsing. Correctly parsing C++ already means understanding namespaces 
and templates. So MinimalAction fell into disuse and bitrot, and 
eventually the entire Action interface was removed. Sema became the only 
action. Anyway, because separating parser and sema tests for C++ doesn't 
make much sense, and to better get a feeling for test coverage, the CXX 
directory was introduced, which contains tests organized by where the 
feature they describe appears in the standard. (This happened long 
before removing Action, by the way.)

Nowadays, if you add a test for C++, it's best to add it to CXX. 
Occasionally we still add them to other directories, though: to PCH if 
it only tests PCH functionality, and to SemaCXX or CodeGenCXX if the 
test is not easily associated with a specific section of the standard. 
(Some features are all over the place.)

Hope that helps.

Sebastian