Add configurable issue ID validation in title

Read a regex pattern from `git config commit-editor.issue-pattern` and
validate that the commit title starts with a matching issue ID followed
by a colon. A new validation bar displays errors and clears
automatically when the title is corrected.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Martin Prpič <martin.prpic@gmail.com>

Author: mprpic

CLAUDE.md

@@ -6,7 +6,7 @@ This document describes how to work with the commit-editor project.
 
 ## Project Structure
 
-```
+```text
 src/commit_editor/
 ├── __init__.py    # Package init with version
 ├── cli.py         # CLI entry point (argparse)

README.md

@@ -14,6 +14,7 @@ with [Textual](https://textual.textualize.io/).
 - **White space**: Trailing white space is automatically stripped when a file is saved; an empty newline is inserted
   at the end of the file if not present.
 - **Signed-off-by toggle**: Quickly add or remove a `Signed-off-by` trailer with a keyboard shortcut
+- **Issue ID validation**: Optionally enforce that commit titles start with an issue ID (e.g. `PROJ-123:`)
 - **Status bar**: Shows current cursor position (line/column) and title length with warnings
 
 ## Installation
@@ -58,6 +59,26 @@ commit-editor path/to/file.txt
 Additional key bindings are noted in the Textual
 [`TextArea` documentation](https://textual.textualize.io/widgets/text_area/#bindings).
 
+## Configuration
+
+### Issue ID Validation
+
+You can require commit titles to start with an issue ID by setting a regex pattern:
+
+```bash
+# Per-repository
+git config commit-editor.issue-pattern 'PROJ-\d+'
+
+# Global
+git config --global commit-editor.issue-pattern 'PROJ-\d+'
+```
+
+The pattern is matched against the **start of the title** and must be followed by a colon (`:`). For example, with
+the pattern `PROJ-\d+`:
+
+- valid: `PROJ-123: fix login bug`
+- invalid: `fix login bug`
+
 ## Commit Message Format
 
 This editor enforces the widely-accepted git commit message conventions:
@@ -68,10 +89,6 @@ This editor enforces the widely-accepted git commit message conventions:
 
 ## Future Improvements
 
-- Support adding a "Co-authored-by" trailer for AI attribution
-- Word-level spellchecking
-- Config file support (`.commit.toml` project or global level or `pyproject.toml`); support tweaking line length limits
-- Jira (or other issue tracker) ID checking (e.g. title starts with `ABC-123: `)
 - Color theme support
 
 ## License

pyproject.toml

@@ -51,3 +51,7 @@ select = ["F", "E", "W", "I", "N"]
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 asyncio_default_fixture_loop_scope = "function"
+
+[tool.mdlint.rules.MD013]
+line_length = 120
+code_blocks = false

src/commit_editor/app.py

@@ -1,3 +1,4 @@
+import re
 from collections.abc import Callable
 from pathlib import Path
 
@@ -13,12 +14,13 @@
 from textual.widgets import Input, OptionList, Static, TextArea
 from textual.widgets._option_list import Option
 
-from commit_editor.git import get_signed_off_by
+from commit_editor.git import get_issue_pattern, get_signed_off_by
 from commit_editor.spelling import WORD_PATTERN, SpellCheckCache
 
 TITLE_MAX_LENGTH = 50
 BODY_MAX_LENGTH = 72
 _SUGGESTION_PREFIX = "Suggestions for"
+_ISSUE_ID_ERROR = "Missing/Invalid issue ID in title!"
 
 AI_COAUTHOR_MODELS = [
     ("Claude Opus 4.6", "noreply@anthropic.com"),
@@ -325,6 +327,51 @@ def get_cursor_position(self) -> tuple[int, int]:
         return row + 1, col + 1
 
 
+class ValidationBar(Static):
+    """Bar for showing validation error messages. Hidden when empty."""
+
+    DEFAULT_CSS = """
+    ValidationBar {
+        height: auto;
+        background: $surface;
+        color: $error;
+        padding: 0 1;
+        display: none;
+    }
+    ValidationBar.has-errors {
+        display: block;
+    }
+    """
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._errors: list[tuple[str, str]] = []
+
+    def set_error(self, key: str, message: str) -> None:
+        """Add or update a validation error by key."""
+        for i, (k, _) in enumerate(self._errors):
+            if k == key:
+                self._errors[i] = (key, message)
+                self._refresh_display()
+                return
+        self._errors.append((key, message))
+        self._refresh_display()
+
+    def clear_error(self, key: str) -> None:
+        """Remove a validation error by key."""
+        self._errors = [(k, m) for k, m in self._errors if k != key]
+        self._refresh_display()
+
+    def _refresh_display(self) -> None:
+        """Update the display based on current errors."""
+        if self._errors:
+            self.update("\n".join(msg for _, msg in self._errors))
+            self.add_class("has-errors")
+        else:
+            self.update("")
+            self.remove_class("has-errors")
+
+
 class StatusBar(Static):
     """Status bar showing cursor position and title length."""
 
@@ -433,9 +480,17 @@ def __init__(self, filename: Path):
         self._original_content = ""
         self._prompt_mode: str | None = None  # Track active prompt type
         self._spell_timer = None
+        self._issue_pattern: re.Pattern[str] | None = None
+        pattern = get_issue_pattern()
+        if pattern:
+            try:
+                self._issue_pattern = re.compile(pattern + r":")
+            except re.error:
+                pass
 
     def compose(self) -> ComposeResult:
         yield CommitTextArea(id="editor", show_line_numbers=True, highlight_cursor_line=True)
+        yield ValidationBar(id="validation")
         yield StatusBar(id="status")
         yield MessageBar(id="message")
 
@@ -450,6 +505,7 @@ def on_mount(self) -> None:
         editor.focus()
 
         self._update_status_bar()
+        self._validate_issue_id()
 
     def check_action(self, action: str, parameters: tuple) -> bool | None:
         """Disable editor actions when in prompt mode."""
@@ -514,6 +570,7 @@ def on_editor_changed(self, event: CommitTextArea.Changed) -> None:
             self.query_one("#message", MessageBar).clear()
 
         self._update_status_bar()
+        self._validate_issue_id()
 
     @on(CommitTextArea.SelectionChanged)
     def on_selection_changed(self, event: CommitTextArea.SelectionChanged) -> None:
@@ -531,6 +588,18 @@ def _update_status_bar(self) -> None:
 
         status.update_status(line, col, title_length, self.dirty)
 
+    def _validate_issue_id(self) -> None:
+        """Validate issue ID in the title and update the validation bar."""
+        if self._issue_pattern is None:
+            return
+        editor = self.query_one("#editor", CommitTextArea)
+        title = editor.text.split("\n")[0] if editor.text else ""
+        validation_bar = self.query_one("#validation", ValidationBar)
+        if self._issue_pattern.match(title):
+            validation_bar.clear_error("issue_id")
+        else:
+            validation_bar.set_error("issue_id", _ISSUE_ID_ERROR)
+
     def _show_message(self, message: str, error: bool = False) -> None:
         """Show a message in the message bar."""
         message_bar = self.query_one("#message", MessageBar)

src/commit_editor/git.py

@@ -31,6 +31,21 @@ def get_user_email() -> str | None:
         return None
 
 
+def get_issue_pattern() -> str | None:
+    try:
+        result = subprocess.run(
+            ["git", "config", "commit-editor.issue-pattern"],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        return result.stdout.strip() or None
+    except subprocess.CalledProcessError:
+        return None
+    except FileNotFoundError:
+        return None
+
+
 def get_signed_off_by() -> str | None:
     name = get_user_name()
     email = get_user_email()

tests/test_app.py

@@ -8,6 +8,7 @@
     CommitEditorApp,
     CommitTextArea,
     MessageBar,
+    ValidationBar,
     _format_coauthor,
 )
 
@@ -612,3 +613,84 @@ async def test_signoff_after_coauthor_no_blank_line(self, temp_file):
                 )
                 # Trailers should be on adjacent lines
                 assert signoff_idx == coauthor_idx + 1
+
+
+class TestIssueIdValidation:
+    """Tests for issue ID validation in commit title."""
+
+    async def test_no_pattern_configured(self, temp_file):
+        """When no pattern is configured, validation bar should be hidden."""
+        temp_file.write_text("Any title without issue ID")
+        with patch("commit_editor.app.get_issue_pattern", return_value=None):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test():
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" not in validation_bar.classes
+
+    async def test_invalid_title_shows_error(self, temp_file):
+        """Invalid title should show error in validation bar."""
+        temp_file.write_text("Fix something")
+        with patch("commit_editor.app.get_issue_pattern", return_value=r"AIPCC-\d+"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test():
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" in validation_bar.classes
+
+    async def test_valid_title_no_error(self, temp_file):
+        """Valid title should not show error in validation bar."""
+        temp_file.write_text("AIPCC-123: Fix something")
+        with patch("commit_editor.app.get_issue_pattern", return_value=r"AIPCC-\d+"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test():
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" not in validation_bar.classes
+
+    async def test_title_becomes_valid_clears_error(self, temp_file):
+        """Error should disappear when title becomes valid."""
+        temp_file.write_text("Fix something")
+        with patch("commit_editor.app.get_issue_pattern", return_value=r"AIPCC-\d+"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test() as pilot:
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" in validation_bar.classes
+
+                # Edit title to be valid
+                editor = app.query_one("#editor", CommitTextArea)
+                editor.load_text("AIPCC-123: Fix something")
+                await pilot.pause()
+
+                assert "has-errors" not in validation_bar.classes
+
+    async def test_error_shown_on_mount(self, temp_file):
+        """Error should be shown immediately on mount with invalid title."""
+        temp_file.write_text("Bad title")
+        with patch("commit_editor.app.get_issue_pattern", return_value=r"AIPCC-\d+"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test():
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" in validation_bar.classes
+
+    async def test_error_persists_while_typing(self, temp_file):
+        """Error should persist while title remains invalid during typing."""
+        temp_file.write_text("Fix something")
+        with patch("commit_editor.app.get_issue_pattern", return_value=r"AIPCC-\d+"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test() as pilot:
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" in validation_bar.classes
+
+                # Type more text (title still invalid)
+                editor = app.query_one("#editor", CommitTextArea)
+                editor.load_text("Fix something else")
+                await pilot.pause()
+
+                assert "has-errors" in validation_bar.classes
+
+    async def test_invalid_regex_treated_as_unconfigured(self, temp_file):
+        """Invalid regex pattern should be treated as unconfigured (no error, no crash)."""
+        temp_file.write_text("Any title")
+        with patch("commit_editor.app.get_issue_pattern", return_value="[invalid"):
+            app = CommitEditorApp(temp_file)
+            async with app.run_test():
+                validation_bar = app.query_one("#validation", ValidationBar)
+                assert "has-errors" not in validation_bar.classes

tests/test_git.py

@@ -1,6 +1,6 @@
 from unittest.mock import patch
 
-from commit_editor.git import get_signed_off_by, get_user_email, get_user_name
+from commit_editor.git import get_issue_pattern, get_signed_off_by, get_user_email, get_user_name
 
 
 class TestGetUserName:
@@ -111,3 +111,50 @@ def test_returns_none_when_email_missing(self):
 
             result = get_signed_off_by()
             assert result is None
+
+
+class TestGetIssuePattern:
+    """Tests for get_issue_pattern function."""
+
+    def test_successful_config_read(self):
+        """Should return the pattern string when git config succeeds."""
+        with patch("commit_editor.git.subprocess.run") as mock_run:
+            mock_run.return_value.stdout = "AIPCC-\\d+\n"
+            mock_run.return_value.returncode = 0
+
+            result = get_issue_pattern()
+            assert result == "AIPCC-\\d+"
+
+            mock_run.assert_called_once_with(
+                ["git", "config", "commit-editor.issue-pattern"],
+                capture_output=True,
+                text=True,
+                check=True,
+            )
+
+    def test_missing_config(self):
+        """Should return None when git config is not set."""
+        with patch("commit_editor.git.subprocess.run") as mock_run:
+            from subprocess import CalledProcessError
+
+            mock_run.side_effect = CalledProcessError(1, "git config")
+
+            result = get_issue_pattern()
+            assert result is None
+
+    def test_git_not_found(self):
+        """Should return None when git is not installed."""
+        with patch("commit_editor.git.subprocess.run") as mock_run:
+            mock_run.side_effect = FileNotFoundError()
+
+            result = get_issue_pattern()
+            assert result is None
+
+    def test_empty_config(self):
+        """Should return None when git config returns empty string."""
+        with patch("commit_editor.git.subprocess.run") as mock_run:
+            mock_run.return_value.stdout = "\n"
+            mock_run.return_value.returncode = 0
+
+            result = get_issue_pattern()
+            assert result is None