New -assume-filename=param to check_clang_tidy.py (like clang-format)

[benhamilton]

Summary

Currently, check_clang_tidy.py includes logic to select default
clang flags based on the extension of the source filename passed
as the first argument.

Since the source filename might be a temporary or test file with an
arbitrary extension unrelated to the file type, this adds the ability
to override the logic the same way clang-format's -assume-filename=
parameter does.

I included a test with a nonstandard file extension. I confirmed
when I modified the warning message that the new test failed,
and that it passed again when I restored the warning message.

Ran tests with:

% cmake -G Ninja /path/to/llvm
% ninja check-clang-tools

[hokein]

LGTM.

test/clang-tidy/check_clang_tidy.py

42 ↗

(On Diff #119175)

It would be clearer to add some documentation for the flag (other flags should have documentation as well, but it is out of scope of this patch)

clang-tools-extra/trunk/test/clang-tidy/check_clang_tidy.py

 r"""
 ClangTidy Test Helper
 =====================
 
 This script runs clang-tidy in fix mode and verify fixes, messages or both.
 
 Usage:
   check_clang_tidy.py [-resource-dir <resource-dir>] \
+    [-assume-filename <file-with-source-extension>] \
     <source-file> <check-name> <temp-file> \
     -- [optional clang-tidy arguments]
 
 Example:
   // RUN: %check_clang_tidy %s llvm-include-order %t -- -- -isystem %S/Inputs
 """
 
 import argparse
 import re
 import subprocess
 import sys
 
 
 def write_file(file_name, text):
   with open(file_name, 'w') as f:
     f.write(text)
     f.truncate()
 
 def main():
   parser = argparse.ArgumentParser()
   parser.add_argument('-resource-dir')
+  parser.add_argument('-assume-filename')
   parser.add_argument('input_file_name')
   parser.add_argument('check_name')
   parser.add_argument('temp_file_name')
 
   args, extra_args = parser.parse_known_args()
 
   resource_dir = args.resource_dir
+  assume_file_name = args.assume_filename
   input_file_name = args.input_file_name
   check_name = args.check_name
   temp_file_name = args.temp_file_name
 
+  file_name_with_extension = assume_file_name or input_file_name
+
   extension = '.cpp'
-  if (input_file_name.endswith('.c')):
+  if (file_name_with_extension.endswith('.c')):
     extension = '.c'
-  if (input_file_name.endswith('.hpp')):
+  if (file_name_with_extension.endswith('.hpp')):
     extension = '.hpp'
   temp_file_name = temp_file_name + extension
 
   clang_tidy_extra_args = extra_args
   if len(clang_tidy_extra_args) == 0:
     clang_tidy_extra_args = ['--', '--std=c++11'] \
         if extension == '.cpp' or extension == '.hpp' else ['--']
 

clang-tools-extra/trunk/test/clang-tidy/nonstandard-file-extension.test

+// RUN: %check_clang_tidy -assume-filename=const-cast.cpp %s cppcoreguidelines-pro-type-const-cast %t
+
+const int *i;
+int *j;
+void f() { j = const_cast<int *>(i); }
+// CHECK-MESSAGES: :[[@LINE-1]]:16: warning: do not use const_cast [cppcoreguidelines-pro-type-const-cast]