Clean up CC and CXX FLAGS tests

[mwichmann]

More consistency, formatting, add test/CXX/SHCCFLAGS.py for symmetry (test/CC/ had one), rename tests to -live since they use a real compiler, and also add that note to docstring. Remove some filename suffix fiddling that wasn't needed because in this usage, SCons figures it out - and we want that as part of the test.

Testsuite-only change.

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt and RELEASE.txt (and read the README.rst).
• I have updated the appropriate documentation

[mwichmann]

using an underscore is basically saying "I know this returns something, and I actually mean to ignore it".

[bdbaddog]

using an underscore is basically saying "I know this returns something, and I actually mean to ignore it".

Yup. I understand that, but I'd rather not sugguest to the community that using the return value for DefaultEnvironment() is a good idea.

[mwichmann]

Then the public interface probably ought not to return anything... yeah, I can get rid of this usage if you're insistent, but it seems worthwhile to quiet IDEs. I guess the use case for it returning an env is so that you can examine it - what compilers did it find, etc.. Should we say in docs that you should not call methods on the returned env? There are some funky internal uses like:

json_node = SCons.Defaults.DefaultEnvironment().arg2nodes(json)

path = SCons.Defaults.DefaultEnvironment()._CacheDir_path

[bdbaddog]

Then the public interface probably ought not to return anything... yeah, I can get rid of this usage if you're insistent, but it seems worthwhile to quiet IDEs. I guess the use case for it returning an env is so that you can examine it - what compilers did it find, etc.. Should we say in docs that you should not call methods on the returned env? There are some funky internal uses like:

json_node = SCons.Defaults.DefaultEnvironment().arg2nodes(json)

path = SCons.Defaults.DefaultEnvironment()._CacheDir_path

There's lots of use in the wild, so changing the return value would break a lot.
It will work, it's just not good practice, so omitting such from our own usage is probably sufficient?

[mwichmann]

There's lots of use in the wild, so changing the return value would break a lot. It will work, it's just not good practice, so omitting such from our own usage is probably sufficient?

$ git grep "=.*DefaultEnvironment" \*.py | wc
     66     226    4598

that's on master, thus omitting the changes from the PR, so there are a bunch of them (three of those are false hits, they're actually DefaultEnvironmentCall, so it's 63 by that unsophisticated grep).

[mwichmann]

Rolled back the assignment, now it's just a bare call.