Allow override of clang-format executable

Because GitHub's Ubuntu image offers multiple version fo clang-format, and
sometimes it seems to prefer a version lower than 12 (which is the minimum
required by our config file), I added an override via the new environment
variable `KALEIDOSCOPE_CODE_FORMATTER`.

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

.github/workflows/build.yml

@@ -36,7 +36,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - run: make check-code-style
+    - run: KALEIDOSCOPE_CODE_FORMATTER=clang-format-12 make check-code-style
   check-shellcheck:
     runs-on: ubuntu-latest
     steps:

bin/format-code.py

@@ -172,7 +172,9 @@ def main():
             return 1
 
     # Locate `clang-format` executable:
-    clang_format_exe = shutil.which('clang-format')
+    clang_format_exe = os.getenv('KALEIDOSCOPE_CODE_FORMATTER')
+    if clang_format_exe is None:
+        clang_format_exe = shutil.which('clang-format')
     logging.debug("Found `clang-format` executable: %s", clang_format_exe)
     clang_format_cmd = [clang_format_exe, '-i']
     if opts.loglevel <= logging.INFO: