feature: add monorepo recursive configuration

Finds all ".pre-commit-config.yaml" files recursively, depending on the
staged files.

Only tested on Linux.

pre_commit/commands/run.py

@@ -9,7 +9,7 @@ import re
 import subprocess
 import time
 import unicodedata
-from typing import Any
+from typing import Any, List
 from typing import Collection
 from typing import MutableMapping
 from typing import Sequence
@@ -317,7 +317,6 @@ def _run_hooks(
             'git', '--no-pager', 'diff', '--no-ext-diff',
             f'--color={git_color_opt}',
         ))
-
     return retval
 
 
@@ -334,6 +333,36 @@ def _has_unstaged_config(config_file: str) -> bool:
     return retcode == 1
 
 
+def _dive_into_file_hierarchy(dir_path: str):
+    """ Iterator for crawling recursively a path.
+    :note!: Not tested on windows (hardcoded '/' for path separator).
+    """
+    accumulated = "" # start from empty string
+    _split = dir_path.split('/')
+    while len(_split) > 0:
+        accumulated = os.path.join(accumulated, _split.pop(0))
+        yield accumulated
+
+def _find_all_config_files(modified_files: List[str], config_file_name: str) -> List[str]:
+    """ Finds all the config files relative to modified files.
+    Every modified file can have a :config_file_name: in its parent directory. If found, get it.
+    """
+
+    ret_set = set()
+    for file_name in modified_files:
+        directory_base = os.path.dirname(file_name)
+        for subdir_seq_item in _dive_into_file_hierarchy(directory_base):
+            candidate_fileconfig = os.path.join(subdir_seq_item, config_file_name)
+            if os.path.exists(candidate_fileconfig):
+                # logging.debug(f"Will use config file: {candidate_fileconfig}")
+                ret_set.add(candidate_fileconfig)
+    # do not forget the root dir !
+    if os.path.exists(config_file_name):
+        # logging.debug(f"Will use config file: {config_file_name}")
+        ret_set.add(config_file_name)
+    ret = sorted(list(ret_set))
+    return ret
+
 def run(
         config_file: str,
         store: Store,
@@ -341,7 +370,6 @@ def run(
         environ: MutableMapping[str, str] = os.environ,
 ) -> int:
     stash = not args.all_files and not args.files
-
     # Check if we have unresolved merge conflict files and fail fast.
     if stash and _has_unmerged_paths():
         logger.error('Unmerged files.  Resolve before committing.')
@@ -419,29 +447,36 @@ def run(
         if stash:
             exit_stack.enter_context(staged_files_only(store.directory))
 
-        config = load_config(config_file)
-        hooks = [
-            hook
-            for hook in all_hooks(config, store)
-            if not args.hook or hook.id == args.hook or hook.alias == args.hook
-            if args.hook_stage in hook.stages
-        ]
+        ret_int = 0
+        # find all applicable config files
+        all_config_files = _find_all_config_files(_all_filenames(args), config_file)
+        for _config_file in all_config_files:
+            config = load_config(_config_file)
+            if len(all_config_files) > 0 :
+                print(f"Hooks from {_config_file}:")
+            hooks = [
+                hook
+                for hook in all_hooks(config, store)
+                if not args.hook or hook.id == args.hook or hook.alias == args.hook
+                if args.hook_stage in hook.stages
+            ]
 
-        if args.hook and not hooks:
-            output.write_line(
-                f'No hook with id `{args.hook}` in stage `{args.hook_stage}`',
-            )
-            return 1
+            if args.hook and not hooks:
+                output.write_line(
+                    f'No hook with id `{args.hook}` in stage `{args.hook_stage}` of file {_config_file}',
+                )
+                return 1
 
-        skips = _get_skips(environ)
-        to_install = [
-            hook
-            for hook in hooks
-            if hook.id not in skips and hook.alias not in skips
-        ]
-        install_hook_envs(to_install, store)
+            skips = _get_skips(environ)
+            to_install = [
+                hook
+                for hook in hooks
+                if hook.id not in skips and hook.alias not in skips
+            ]
+            install_hook_envs(to_install, store)
 
-        return _run_hooks(config, hooks, skips, args)
+            ret_int += _run_hooks(config, hooks, skips, args)  # accumulate errors
+        return ret_int
 
     # https://github.com/python/mypy/issues/7726
     raise AssertionError('unreachable')