Add hook to check the file can be parsed as Python.

doc-source/hooks.rst

@@ -30,6 +30,15 @@ Pull ``# noqa: ...`` comments that immediately follow docstrings back up to the
 This hook takes no arguments.
 
 
+``check_ast``
+--------------------
+
+Check the source can be parsed as a Python Abstract Syntax Tree.
+This could be called early in the execution -- to check the file is valid before starting reformatting -- and again at the end to ensure no errors were introduced by the reformatting.
+
+This hook takes no arguments.
+
+
 ``ellipsis_reformat``
 -----------------------
 

formate/mini_hooks.py

@@ -27,9 +27,10 @@
 #
 
 # stdlib
+import ast
 import re
 
-__all__ = ["noqa_reformat"]
+__all__ = ["noqa_reformat", "check_ast"]
 
 
 def noqa_reformat(source: str) -> str:
@@ -42,3 +43,16 @@ def noqa_reformat(source: str) -> str:
 	"""
 
 	return re.sub(r'"""[\n\s]+#\s+noqa', '"""  # noqa', source)
+
+
+def check_ast(source: str) -> str:
+	"""
+	Check the source can be parsed as a Python Abstract Syntax Tree.
+
+	:param source: The source to check.
+
+	:raises SyntaxError: If the source is not valid Python.
+	"""
+
+	ast.parse(source)
+	return source

tests/test_integration.py

@@ -3,8 +3,8 @@
 
 # 3rd party
 import pytest
-from coincidence.selectors import not_pypy, only_pypy
 from coincidence.regressions import AdvancedDataRegressionFixture, check_file_output, check_file_regression
+from coincidence.selectors import not_pypy, only_pypy
 from consolekit.terminal_colours import strip_ansi
 from consolekit.testing import CliRunner, Result
 from domdf_python_tools.paths import PathPlus, in_directory

tests/test_mini_hooks.py

@@ -1,5 +1,8 @@
+# 3rd party
+import pytest
+
 # this package
-from formate.mini_hooks import noqa_reformat
+from formate.mini_hooks import check_ast, noqa_reformat
 
 
 def test_noqa_reformat():
@@ -20,3 +23,40 @@ def test_noqa_reformat():
 	assert noqa_reformat('\n'.join(code)) == '\n'.join(expected)
 
 	assert noqa_reformat('\n'.join(expected)) == '\n'.join(expected)
+
+
+def test_check_ast():
+	code = [
+			"def foo(:",
+			'\t"""',
+			"\tDoes something,",
+			'\t"""',
+			'',
+			"  # noqa: D400  ",
+			]
+
+	with pytest.raises(SyntaxError):
+		check_ast('\n'.join(code))
+
+	code = [
+			"def foo():",
+			'"""',
+			"\tDoes something,",
+			'\t"""',
+			'',
+			"  # noqa: D400  ",
+			]
+
+	with pytest.raises(SyntaxError):
+		check_ast('\n'.join(code))
+
+	code = [
+			"def foo():",
+			'\t"""',
+			"\tDoes something,",
+			'\t"""',
+			'',
+			"  # noqa: D400  ",
+			]
+
+	assert check_ast('\n'.join(code)) == '\n'.join(code)