Speed up clang-tidy CI by 80%+ with incremental checking (#9396)

script/clang-tidy

@@ -22,6 +22,7 @@ from helpers import (
     git_ls_files,
     load_idedata,
     print_error_for_file,
+    print_file_list,
     root_path,
     temp_header_file,
 )
@@ -218,13 +219,14 @@ def main():
     )
     args = parser.parse_args()
 
-    idedata = load_idedata(args.environment)
-    options = clang_options(idedata)
-
     files = []
     for path in git_ls_files(["*.cpp"]):
         files.append(os.path.relpath(path, os.getcwd()))
 
+    # Print initial file count if it's large
+    if len(files) > 50:
+        print(f"Found {len(files)} total files to process")
+
     if args.files:
         # Match against files specified on command-line
         file_name_re = re.compile("|".join(args.files))
@@ -240,10 +242,28 @@ def main():
 
     if args.split_num:
         files = split_list(files, args.split_num)[args.split_at - 1]
+        print(f"Split {args.split_at}/{args.split_num}: checking {len(files)} files")
 
+    # Print file count before adding header file
+    print(f"\nTotal files to check: {len(files)}")
+
+    # Early exit if no files to check
+    if not files:
+        print("No files to check - exiting early")
+        return 0
+
+    # Only build header file if we have actual files to check
     if args.all_headers and args.split_at in (None, 1):
         build_all_include()
         files.insert(0, temp_header_file)
+        print(f"Added all-include header file, new total: {len(files)}")
+
+    # Print final file list before loading idedata
+    print_file_list(files, "Final files to process:")
+
+    # Load idedata and options only if we have files to check
+    idedata = load_idedata(args.environment)
+    options = clang_options(idedata)
 
     tmpdir = None
     if args.fix: