[lit] use built-in clear_environment instead of external env command

[inglorion]

Summary

r366980 made lit invocations instead invoke env ...options... lit. This
invokes the external env command, which we generally avoid (as per
r242696). This change replaces the env invocation by lit's built-in
clear_environment configuration functionality.

[rnk]

I think this ended up being reverted in rL367627, see the discussion on the review:
https://reviews.llvm.org/D65156#1610296

I suppose you can abandon this and @jdenny can use this solution or come up with a different one.

[inglorion]

Heh, I just missed the revert. @jdenny, feel free to use this as inspiration.

[jdenny]

In D65619#1611360, @inglorion wrote:

Heh, I just missed the revert. @jdenny, feel free to use this as inspiration.

Thanks. :-)

I believe that also clears those variables for the outer lit running lit's test suite. I only wanted to clear them for the %{lit} calls within lit's test suite.

llvm/utils/lit/tests/lit.cfg

 llvm_src_root = getattr(config, 'llvm_src_root', None)
 if llvm_src_root:
   # ``test_source_root`` may be in LLVM's binary build directory which does not contain
   # ``lit.py``, so use `llvm_src_root` instead.
   lit_path = os.path.join(llvm_src_root, 'utils', 'lit')
 else:
   lit_path = os.path.join(config.test_source_root, '..')
 
+# This test suite calls %{lit} to test lit's behavior for the sample test
+# suites in %{inputs}.  This test suite's results are then determined in part
+# by %{lit}'s textual output, which includes the output of FileCheck calls
+# within %{inputs}'s test suites.  Thus, %{lit} clears environment variables
+# that can affect FileCheck's output.
+llvm_config.clear_environment(['FILECHECK_OPTS', 'FILECHECK_DUMP_INPUT_ON_FAILURE'])
+
 # Required because some tests import the lit module
 llvm_config.with_environment('PYTHONPATH', lit_path, append_path=True)
 
 # Add llvm and lit tools directories if this config is being loaded indirectly.
 for attribute in ('llvm_tools_dir', 'lit_tools_dir'):
     directory = getattr(config, attribute, None)
     if directory:
         llvm_config.with_environment('PATH', directory, append_path=True)
 
-# This test suite calls %{lit} to test lit's behavior for the sample test
-# suites in %{inputs}.  This test suite's results are then determined in part
-# by %{lit}'s textual output, which includes the output of FileCheck calls
-# within %{inputs}'s test suites.  Thus, %{lit} clears environment variables
-# that can affect FileCheck's output.
 config.substitutions.append(('%{inputs}', os.path.join(
     config.test_source_root, 'Inputs')))
 config.substitutions.append(('%{lit}',
-    "{env} %{{python}} {lit}".format(
-        env="env FILECHECK_OPTS= FILECHECK_DUMP_INPUT_ON_FAILURE=",
+    "%{{python}} {lit}".format(
         lit=os.path.join(lit_path, 'lit.py'))))
 config.substitutions.append(('%{python}', '"%s"' % (sys.executable)))
 
 # Enable coverage.py reporting, assuming the coverage module has been installed
 # and sitecustomize.py in the virtualenv has been modified appropriately.
 if lit_config.params.get('check-coverage', None):
     config.environment['COVERAGE_PROCESS_START'] = os.path.join(
         os.path.dirname(__file__), ".coveragerc")