[lit] lit.site.cfg.py: support symlinked lit.site.cfg.py files

[milianw]

Summary

Use os.path.realpath(__file__) instead of os.path.abspath(__file__)
to get an absolute path pointing to the lit.site.cfg.py in the
build directory. That way one can symlink the generated
lit.site.cfg.py file into the source directory and run lit seamlessly
on individual files.

Before:

$ ln -s .../build/llvm-project/tools/clang/test/lit.site.cfg.py
$ lit --debug Index/cxx17-structured-binding.cpp
lit: .../lit/discovery.py:63: note: loading suite config '.../src/llvm-project/clang/test/lit.site.cfg.py'
...
lit: .../lit/LitConfig.py:115: note: load_config from '.../llvm-project/clang/test/lit.cfg.py'
lit: .../lit/TestingConfig.py:100: fatal: unable to parse config file '.../src/llvm-project/clang/test/lit.site.cfg.py', traceback: Traceback (most recent call last):
  File ".../lit/TestingConfig.py", line 89, in load_from_path
    exec(compile(data, path, 'exec'), cfg_globals, None)
  File ".../src/llvm-project/clang/test/lit.site.cfg.py", line 64, in <module>
    lit_config.load_config(
  File ".../lit/LitConfig.py", line 116, in load_config
    config.load_from_path(path, self)
  File ".../lit/TestingConfig.py", line 76, in load_from_path
    f = open(path)
FileNotFoundError: [Errno 2] No such file or directory: '.../src/llvm-project/clang/test/lit.cfg.py'

After:

$ ln -s .../build/llvm-project/tools/clang/test/lit.site.cfg.py
$ lit --debug Index/cxx17-structured-binding.cpp
lit: .../lit/discovery.py:63: note: loading suite config '.../src/llvm-project/clang/test/lit.site.cfg.py'
...
lit: .../lit/llvm/config.py:342: note: using clang: .../build/llvm-project/bin/clang
...
-- Testing: 1 tests, 1 workers --
...

[milianw]

fixup commit message

[thakis]

Doesn't this Just Work if you just _not_ create that symlink?

% ../../out/gn/bin/llvm-lit Index/cxx11-lambdas.cpp
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:343: note: using clang: /Users/thakis/src/llvm-project/out/gn/bin/clang
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/util.py:408: note: using SDKROOT: u'/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk'
-- Testing: 1 tests, 1 workers --
PASS: Clang :: Index/cxx11-lambdas.cpp (1 of 1)

Testing Time: 1.03s
  Expected Passes: 1

[milianw]

nope, without the symlink I get:

lit Index/cxx11-lambdas.cpp 
lit: /home/milian/.local/lib/python3.8/site-packages/lit/TestingConfig.py:100: fatal: unable to parse config file '/home/milian/projects/src/llvm-project/clang/test/lit.cfg.py', traceback: Traceback (most recent call last):
  File "/home/milian/.local/lib/python3.8/site-packages/lit/TestingConfig.py", line 89, in load_from_path
    exec(compile(data, path, 'exec'), cfg_globals, None)
  File "/home/milian/projects/src/llvm-project/clang/test/lit.cfg.py", line 25, in <module>
    config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
AttributeError: 'NoneType' object has no attribute 'use_lit_shell'

[thakis]

Can you describe your setup a bit more? You're using an installed lit? Does it work if you use llvm-lit in your bin/ dir in your build dir?

[milianw]

I'm using lit 0.10.0 installed via pip 20.0.2 using python 3.8.2

source dir: /home/milian/projects/src/llvm-project
build dir: /home/milian/projects/build/llvm-project

it indeed works fine with llvm-lit. why is that not installed?

[thakis]

It's build config dependent. Is there an advantage to using pip-installed lit vs the lit in the build dir (which trampolines to the one in the source dir)?

If this patch here fixes a problem for you, I don't have a problem with landing this, but your setup seems a bit uncommon to me and you might run into fewer problems over time if you use the setup that most folks seem to use.

[milianw]

with this patch I could just use the global lit and don't need to add the build dir to my PATH. But, thinking about it, I can also symlink llvm-lit into a custom folder in my PATH and see if that works. If you don't want to merge this, I'll abandon it, please tell me if you would prefer it like that.

llvm/cmake/modules/AddLLVM.cmake

string(CONCAT LLVM_LIT_PATH_FUNCTION
   # Lit converts config paths to lower case in discovery.py, before
   # loading the config. This causes __file__ to be all lower-case (including
   # the drive letter), but several clang tests pass -include %s and a
   # clang warning checks that passed case matches on-disk cache. So it's
   # important that this restores the on-disk case of the prefix.
   "# Allow generated file to be relocatable.\n"
   "def path(p):\n"
   "  if not p: return ''\n"
-  "  p = os.path.join(os.path.dirname(os.path.abspath(__file__)), p)\n"
+  "  p = os.path.join(os.path.dirname(os.path.realpath(__file__)), p)\n"
   "  p = os.path.normpath(p).replace(os.sep, '/')\n"
   "  if os.name == 'nt' and os.path.isabs(p): return p[0].upper() + p[1:]\n"
   "  return p\n"
   )
 
 # This function provides an automatic way to 'configure'-like generate a file
 # based on a set of common and custom variables, specifically targeting the
 # variables needed for the 'lit.site.cfg' files. This function bundles the