implement fluent (ftl) check

Fluent is file format used by Firefox and other programs for translation strings.

pre_commit_hooks/check_fluent.py

@@ -0,0 +1,137 @@
+from __future__ import annotations
+
+import argparse
+from collections.abc import Sequence
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*', help='Filenames to check.')
+    args = parser.parse_args(argv)
+
+    retval = 0
+    for filename in args.filenames:
+        try:
+            with open(filename, encoding='UTF-8') as f:
+                content = f.read()
+
+            if not _validate_fluent_syntax(content, filename):
+                retval = 1
+
+        except (OSError, UnicodeDecodeError) as exc:
+            print(f"{filename}: Failed to read file ({exc})")
+            retval = 1
+
+    return retval
+
+
+def _validate_fluent_syntax(content: str, filename: str) -> bool:
+    """Validate Fluent FTL file syntax."""
+    lines = content.splitlines()
+    errors = []
+
+    # Track current message context
+    current_message = None
+    has_default_variant = False
+    in_select_expression = False
+
+    for line_num, line in enumerate(lines, 1):
+        # Skip empty lines and comments
+        if not line.strip() or line.strip().startswith('#'):
+            continue
+
+        # Check for message definitions (identifier = value)
+        if (
+            '=' in line and
+            not line.startswith(' ') and
+            not line.startswith('\t')
+        ):
+            current_message = line.split('=')[0].strip()
+            in_select_expression = False
+            has_default_variant = False
+
+            # Validate message identifier
+            if not _is_valid_identifier(current_message):
+                errors.append(
+                    f"Line {line_num}: Invalid message identifier "
+                    f'"{current_message}"',
+                )
+
+            # Check for select expressions (contains -> or other select syntax)
+            if '{' in line and '$' in line and '->' in line:
+                in_select_expression = True
+
+        # Handle indented content (attributes, variants, multiline values)
+        elif line.startswith(' ') or line.startswith('\t'):
+            if current_message is None:
+                errors.append(
+                    f"Line {line_num}: Indented content without "
+                    f"message context",
+                )
+                continue
+
+            stripped = line.strip()
+
+            # Check for attribute definitions
+            if stripped.startswith('.') and '=' in stripped:
+                # Remove leading dot
+                attr_name = stripped.split('=')[0].strip()[1:]
+                if not _is_valid_identifier(attr_name):
+                    errors.append(
+                        f"Line {line_num}: Invalid attribute identifier "
+                        f'"{attr_name}"',
+                    )
+
+            # Check for variants in select expressions
+            elif stripped.startswith('*') or (
+                stripped.startswith('[') and stripped.endswith(']')
+            ):
+                if not in_select_expression:
+                    errors.append(
+                        f"Line {line_num}: Variant definition outside "
+                        f"select expression",
+                    )
+                elif stripped.startswith('*'):
+                    has_default_variant = True
+                else:
+                    # Non-* variants don't set has_default_variant
+                    pass
+
+        # Check for unterminated select expressions
+        if in_select_expression and current_message:
+            if '}' in line:
+                in_select_expression = False
+                if not has_default_variant:
+                    errors.append(
+                        f"Line {line_num}: Select expression missing "
+                        f"default variant (marked with *)",
+                    )
+
+    # Report errors
+    if errors:
+        for error in errors:
+            print(f"{filename}: {error}")
+        return False
+
+    return True
+
+
+def _is_valid_identifier(identifier: str) -> bool:
+    """Check if identifier follows Fluent naming conventions."""
+    if not identifier:
+        return False
+
+    # Must start with letter
+    if not identifier[0].isalpha():
+        return False
+
+    # Can contain letters, numbers, underscores, and hyphens
+    for char in identifier:
+        if not (char.isalnum() or char in '_-'):
+            return False
+
+    return True
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())