feat: support .archignore exclusions

BACKLOG.md

@@ -11,7 +11,7 @@ This backlog collects product and maintenance ideas from project research.
 
 ## P1 - Adoption Workflow
 
-- Add an `.archignore` or similar file, modeled after `.gitignore`, for files that should never be analyzed.
+- [x] Add an `.archignore` or similar file, modeled after `.gitignore`, for files that should never be analyzed.
 - Add a `.because(...)` API so rules can carry user-facing rationale into failure messages and generated architecture documentation.
 - Add configuration-file support for common rules, while keeping the fluent Python API as the primary interface.
 - Add support for monorepo and multi-package Python projects.

README.md

@@ -137,6 +137,25 @@ options = CheckOptions(
 violations = rule.check(options)
 ```
 
+### Excluding Files With `.archignore`
+
+Add a `.archignore` file to your project root to permanently exclude generated or
+irrelevant files from architecture checks and file-based metrics:
+
+```gitignore
+# Generated code
+generated/
+
+# Migration scripts
+migrations/*.py
+
+# A single root-level file
+/legacy_adapter.py
+```
+
+Patterns support comments, blank lines, glob syntax, root-relative paths, path
+patterns, and directory patterns with a trailing `/`.
+
 ## 🐹 Use Cases
 
 Here is an overview of common use cases.

scripts/check_release_metadata.py

@@ -17,7 +17,7 @@ def read_project_version() -> str:
     content = PYPROJECT.read_text(encoding="utf-8")
     match = re.search(r'^version = "([^"]+)"$', content, re.MULTILINE)
     if match is None:
-        raise RuntimeError("Could not find project.version in pyproject.toml")
+        raise RuntimeError("Could not find [project].version in pyproject.toml")
     return match.group(1)
 
 

src/archunitpython/common/extraction/extract_graph.py

@@ -27,6 +27,8 @@
     "*.egg-info",
 ]
 
+_ARCHIGNORE_FILE = ".archignore"
+
 
 def clear_graph_cache(options: CheckOptions | None = None) -> None:
     """Clear the cached dependency graphs."""
@@ -58,7 +60,7 @@ def extract_graph(
         project_path = os.getcwd()
 
     project_path = os.path.abspath(project_path)
-    excludes = list(exclude_patterns) if exclude_patterns is not None else list(_DEFAULT_EXCLUDE)
+    excludes = _resolve_exclude_patterns(project_path, exclude_patterns)
     ignore_type_checking_imports = bool(
         options and options.ignore_type_checking_imports
     )
@@ -94,6 +96,34 @@ def _build_cache_key(
     )
 
 
+def _resolve_exclude_patterns(
+    project_path: str,
+    exclude_patterns: list[str] | None,
+) -> list[str]:
+    """Resolve exclude patterns (explicit or defaults) plus any .archignore patterns."""
+    excludes = list(exclude_patterns) if exclude_patterns is not None else list(_DEFAULT_EXCLUDE)
+    excludes.extend(_load_archignore_patterns(project_path))
+    return excludes
+
+
+def _load_archignore_patterns(project_path: str) -> list[str]:
+    """Load .archignore patterns from a project root, if present."""
+    archignore_path = os.path.join(project_path, _ARCHIGNORE_FILE)
+    try:
+        with open(archignore_path, "r", encoding="utf-8", errors="replace") as f:
+            lines = f.readlines()
+    except OSError:
+        return []
+
+    patterns: list[str] = []
+    for line in lines:
+        pattern = line.strip()
+        if not pattern or pattern.startswith("#"):
+            continue
+        patterns.append(pattern)
+    return patterns
+
+
 def _extract_graph_uncached(
     project_path: str,
     exclude_patterns: list[str],
@@ -105,6 +135,7 @@ def _extract_graph_uncached(
 
     edges: list[Edge] = []
     py_files_set = set(py_files)
+    normalized_py_files = {_normalize(f) for f in py_files_set}
 
     for file_path in py_files:
         # Add self-referencing edge (ensures the file appears as a node)
@@ -129,10 +160,8 @@ def _extract_graph_uncached(
             )
             if resolved and resolved != _normalize(file_path):
                 # Check if the resolved path is in our project
-                if not is_external and resolved not in {
-                    _normalize(f) for f in py_files_set
-                }:
-                    is_external = True
+                if not is_external and resolved not in normalized_py_files:
+                    continue
 
                 edges.append(
                     Edge(
@@ -154,29 +183,65 @@ def _normalize(path: str) -> str:
 def _find_python_files(root: str, exclude: list[str]) -> list[str]:
     """Recursively find all .py files, excluding specified patterns."""
     py_files: list[str] = []
+    root = os.path.abspath(root)
     for dirpath, dirnames, filenames in os.walk(root):
         # Filter out excluded directories in-place
         dirnames[:] = [
             d
             for d in dirnames
-            if not _should_exclude(d, exclude)
+            if not _should_exclude_path(os.path.join(dirpath, d), root, exclude, is_dir=True)
         ]
 
         for filename in filenames:
-            if filename.endswith(".py") and not _should_exclude(filename, exclude):
-                full_path = os.path.join(dirpath, filename)
+            full_path = os.path.join(dirpath, filename)
+            if filename.endswith(".py") and not _should_exclude_path(
+                full_path, root, exclude, is_dir=False
+            ):
                 py_files.append(os.path.abspath(full_path))
 
     return py_files
 
 
-def _should_exclude(name: str, patterns: list[str]) -> bool:
-    """Check if a name matches any exclude pattern."""
+def _should_exclude_path(
+    path: str,
+    root: str,
+    patterns: list[str],
+    *,
+    is_dir: bool,
+) -> bool:
+    """Check if a path matches any exclude pattern."""
     import fnmatch
 
-    for pattern in patterns:
-        if fnmatch.fnmatch(name, pattern):
+    rel_path = _normalize(os.path.relpath(path, root))
+    name = os.path.basename(path)
+
+    for raw_pattern in patterns:
+        pattern = raw_pattern.strip().replace("\\", "/")
+        if not pattern or pattern.startswith("#"):
+            continue
+
+        pattern = pattern.removeprefix("./")
+        anchored = pattern.startswith("/")
+        if anchored:
+            pattern = pattern[1:]
+
+        dir_only = pattern.endswith("/")
+        if dir_only:
+            pattern = pattern.rstrip("/")
+            if not is_dir:
+                continue
+
+        if not pattern:
+            continue
+
+        if "/" in pattern or anchored:
+            if fnmatch.fnmatch(rel_path, pattern):
+                return True
+            if is_dir and rel_path == pattern:
+                return True
+        elif fnmatch.fnmatch(name, pattern):
             return True
+
     return False
 
 

src/archunitpython/metrics/extraction/extract_class_info.py

@@ -5,7 +5,10 @@
 import ast
 import os
 
-from archunitpython.common.extraction.extract_graph import _DEFAULT_EXCLUDE, _find_python_files
+from archunitpython.common.extraction.extract_graph import (
+    _find_python_files,
+    _resolve_exclude_patterns,
+)
 from archunitpython.metrics.common.types import (
     ClassInfo,
     EnhancedClassInfo,
@@ -33,7 +36,7 @@ def extract_class_info(
         project_path = os.getcwd()
 
     project_path = os.path.abspath(project_path)
-    excludes = exclude_patterns if exclude_patterns is not None else _DEFAULT_EXCLUDE
+    excludes = _resolve_exclude_patterns(project_path, exclude_patterns)
     py_files = _find_python_files(project_path, excludes)
 
     classes: list[ClassInfo] = []
@@ -53,7 +56,7 @@ def extract_enhanced_class_info(
         project_path = os.getcwd()
 
     project_path = os.path.abspath(project_path)
-    excludes = exclude_patterns if exclude_patterns is not None else _DEFAULT_EXCLUDE
+    excludes = _resolve_exclude_patterns(project_path, exclude_patterns)
     py_files = _find_python_files(project_path, excludes)
 
     results: list[FileAnalysisResult] = []

src/archunitpython/metrics/fluentapi/metrics.py

@@ -267,13 +267,13 @@ def check(self, options: CheckOptions | None = None) -> list[Violation]:
         import os
 
         from archunitpython.common.extraction.extract_graph import (
-            _DEFAULT_EXCLUDE,
             _find_python_files,
+            _resolve_exclude_patterns,
         )
 
         project = self._project_path or os.getcwd()
         project = os.path.abspath(project)
-        files = _find_python_files(project, _DEFAULT_EXCLUDE)
+        files = _find_python_files(project, _resolve_exclude_patterns(project, None))
         violations: list[Violation] = []
 
         for file_path in files:

tests/common/test_extract_graph.py

@@ -11,6 +11,7 @@
     _extract_imports,
     _find_python_files,
     _normalize,
+    _resolve_exclude_patterns,
     clear_graph_cache,
     extract_graph,
 )
@@ -132,6 +133,73 @@ def test_edge_has_import_kinds(self):
         assert len(edges_with_kinds) > 0
 
 
+class TestArchignore:
+    def setup_method(self):
+        clear_graph_cache()
+        self._temp_dir = Path(__file__).resolve().parent / ".tmp" / f"project_{uuid4().hex}"
+        self._temp_dir.mkdir(parents=True)
+
+    def teardown_method(self):
+        shutil.rmtree(self._temp_dir, ignore_errors=True)
+
+    def _write(self, relative_path: str, content: str = "") -> None:
+        path = self._temp_dir / relative_path
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_text(content, encoding="utf-8")
+
+    def test_archignore_excludes_files_and_directories(self):
+        self._write(
+            ".archignore",
+            "\n".join(
+                [
+                    "# Ignore generated architecture-test inputs",
+                    "ignored.py",
+                    "generated/",
+                    "nested/*.py",
+                    "/root_ignored.py",
+                ]
+            ),
+        )
+        self._write("keep.py")
+        self._write("ignored.py")
+        self._write("root_ignored.py")
+        self._write("generated/generated.py")
+        self._write("nested/ignored_nested.py")
+
+        excludes = _resolve_exclude_patterns(str(self._temp_dir), ["__pycache__"])
+        files = _find_python_files(str(self._temp_dir), excludes)
+        relative_files = {
+            Path(file_path).relative_to(self._temp_dir).as_posix()
+            for file_path in files
+        }
+
+        assert relative_files == {"keep.py"}
+
+    def test_archignore_ignored_files_are_not_dependency_targets(self):
+        self._write(".archignore", "ignored.py\n")
+        self._write("keep.py", "import ignored\n")
+        self._write("ignored.py", "VALUE = 1\n")
+
+        graph = extract_graph(str(self._temp_dir))
+        targets = {edge.target for edge in graph}
+
+        ignored_path = _normalize(str((self._temp_dir / "ignored.py").resolve()))
+        assert ignored_path not in targets
+
+    def test_archignore_with_invalid_utf8_bytes_does_not_abort_extraction(self):
+        (self._temp_dir / ".archignore").write_bytes(b"ignored.py\n\xff\n")
+        self._write("keep.py")
+        self._write("ignored.py")
+
+        graph = extract_graph(str(self._temp_dir))
+        sources = {edge.source for edge in graph}
+
+        keep_path = _normalize(str((self._temp_dir / "keep.py").resolve()))
+        ignored_path = _normalize(str((self._temp_dir / "ignored.py").resolve()))
+        assert keep_path in sources
+        assert ignored_path not in sources
+
+
 class TestTypeCheckingImportHandling:
     def setup_method(self):
         clear_graph_cache()

tests/metrics/test_metrics_fluentapi.py

@@ -1,6 +1,9 @@
 """Tests for the metrics fluent API."""
 
 import os
+import shutil
+from pathlib import Path
+from uuid import uuid4
 
 from archunitpython.metrics.assertion.metric_thresholds import (
     FileCountViolation,
@@ -58,6 +61,29 @@ def test_lines_of_code_violation(self):
         assert len(file_violations) > 0
 
 
+class TestMetricsArchignore:
+    def setup_method(self):
+        self._temp_dir = Path(__file__).resolve().parent / ".tmp" / f"project_{uuid4().hex}"
+        self._temp_dir.mkdir(parents=True)
+
+    def teardown_method(self):
+        shutil.rmtree(self._temp_dir, ignore_errors=True)
+
+    def test_file_metrics_respect_archignore(self):
+        (self._temp_dir / ".archignore").write_text("ignored.py\n", encoding="utf-8")
+        (self._temp_dir / "keep.py").write_text("VALUE = 1\n", encoding="utf-8")
+        (self._temp_dir / "ignored.py").write_text(
+            "\n".join(f"VALUE_{i} = {i}" for i in range(20)),
+            encoding="utf-8",
+        )
+
+        violations = (
+            metrics(str(self._temp_dir)).count().lines_of_code().should_be_below(5).check()
+        )
+
+        assert violations == []
+
+
 class TestLCOMMetricsFluentAPI:
     def test_lcom96b_below(self):
         violations = (