Add compile_commands.json to git staging and fix Windows diagnostic name

Two fixes:
1. Add compile_commands.json to git staging area in integration tests
   so iwyu can find it when running through pre-commit
2. Normalize Windows clang diagnostic name 'return-mismatch' to 'return-type'
   for consistent test expectations across platforms

Author: pocc

tests/test_hooks.py

@@ -414,6 +414,9 @@ def run_integration_test(cmd_name, files, args, test_dir, target_output, target_
         # Newer cppcheck versions include a checkers report info line
         if cmd_name == "cppcheck":
             output_actual = re.sub(rb"\nnofile:0:0: information: Active checkers.*\n+", b"\n", output_actual)
+        # Windows clang uses return-mismatch instead of return-type
+        if cmd_name in ["clang-tidy", "include-what-you-use"]:
+            output_actual = output_actual.replace(b"clang-diagnostic-return-mismatch", b"clang-diagnostic-return-type")
 
         utils.assert_equal(target_output, output_actual)
         assert target_retcode == actual_returncode
@@ -455,6 +458,9 @@ def run_shell_cmd(cmd_name, files, args, _, target_output, target_retcode):
         # Newer cppcheck versions include a checkers report info line
         if cmd_name == "cppcheck":
             actual = re.sub(rb"\nnofile:0:0: information: Active checkers.*\n+", b"\n", actual)
+        # Windows clang uses return-mismatch instead of return-type
+        if cmd_name in ["clang-tidy", "include-what-you-use"]:
+            actual = actual.replace(b"clang-diagnostic-return-mismatch", b"clang-diagnostic-return-type")
         retcode = sp_child.returncode
         utils.assert_equal(target_output, actual)
         assert target_retcode == retcode

tests/test_utils.py

@@ -115,9 +115,10 @@ def integration_test(cmd_name, files, args, test_dir):
                 fd.write(test_file_strs[test_file_base])
     # Create compilation database for clang-tidy and iwyu
     set_compilation_db(files)
-    # Add only the files we are testing
+    # Add the files we are testing and the compilation database
     run_in(["git", "reset"], test_dir)
-    run_in(["git", "add"] + files, test_dir)
+    compile_db = os.path.join(test_dir, "compile_commands.json")
+    run_in(["git", "add"] + files + [compile_db], test_dir)
     args = list(args)  # redeclare so there's no memory weirdness
     pre_commit_config_path = os.path.join(test_dir, ".pre-commit-config.yaml")
     pre_commit_config = f"""\