fix: change subprocess.Popen calls to work on Linux too (#14689)

* fix: remove 'shell=True' when calling 'git diff'

Calling subprocess.Popen() with a list of args and shell=True causes
the args to be ignored, so ['git', 'diff', '--name-only', '--staged']
was turning into just 'git'. Instead of getting a list of changed
files, we got the --help message.

Two possible fixes: change it from a list to a single string, or remove
'shell=True'. The shell doesn't seem to be needed, so I chose that.

More reading: https://stackoverflow.com/questions/26417658/subprocess-call-arguments-ignored-when-using-shell-true-w-list

* fix: remove 'shell=True' when calling clang-format

Same problem / rationale as previous commit.

* fix: re-add shell=True for win; use different fix

script/run-clang-format.py

@@ -107,11 +107,11 @@ def run_clang_format_diff(args, file_name):
     invocation = [args.clang_format_executable, file_name]
     try:
         proc = subprocess.Popen(
-            invocation,
+            ' '.join(invocation),
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             universal_newlines=True,
-            shell = True)
+            shell=True)
     except OSError as exc:
         raise DiffError(str(exc))
     proc_stdout = proc.stdout
@@ -253,10 +253,10 @@ def main():
     parse_files = []
     if args.changed:
         popen = subprocess.Popen(
-            ["git", "diff", "--name-only", "--cached"],
+            'git diff --name-only --cached',
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT,
-            shell = True
+            shell=True
         )
         for line in popen.stdout:
             file_name = line.rstrip()