Fix: handle verbose include/exclude patterns in pyproject.toml

If a verbose pattern was being used in pyproject.toml, the
patterns did not function correctly. For instance, the pattern

exclude = '''
(
/(
  folder1
| folder2
)/
)
'''

does not function properly. This pattern is inspired by the
pattern that black themselves use:
https://github.com/python/black/blob/master/pyproject.toml

Solve this issue by removing newlines, and formatting
the pattern before using it. This is done the same way
as black themselves are doing it.

pytest_black.py

@@ -49,7 +49,12 @@ def __init__(self, fspath, parent):
         self.add_marker("black")
         try:
             with open("pyproject.toml") as toml_file:
-                self.pyproject = toml.load(toml_file)["tool"]["black"]
+                settings = toml.load(toml_file)["tool"]["black"]
+            if "include" in settings.keys():
+                settings["include"] = self._re_fix_verbose(settings["include"])
+            if "exclude" in settings.keys():
+                settings["exclude"] = self._re_fix_verbose(settings["exclude"])
+            self.pyproject = settings
         except Exception:
             self.pyproject = {}
 
@@ -97,6 +102,11 @@ def _excluded(self):
             return False
         return re.search(self.pyproject["exclude"], str(self.fspath))
 
+    def _re_fix_verbose(self, regex):
+        if "\n" in regex:
+            regex = "(?x)" + regex
+        return re.compile(regex)
+
 
 class BlackError(Exception):
     pass

tests/test_black.py

@@ -96,6 +96,43 @@ def hello():
     result.assert_outcomes(skipped=1, passed=0)
 
 
+def test_exclude_folder(testdir):
+    """Assert test is skipped for files in a folder
+    """
+    testdir.makefile(
+        "pyproject.toml",
+        """
+        [tool.black]
+            exclude = '''
+            (
+              /(
+                  first_folder
+                | ignore_folder
+              )/
+            )
+    '''
+    """,
+    )
+    p = testdir.makepyfile(
+        """
+        def hello():
+            print("Hello, world!")
+    """
+    )
+    # replace trailing newline (stripped by testdir.makepyfile)
+    p = p.write(p.read() + "\n")
+
+    # Move file into folder that should be excluded
+    ignore_folder = testdir.mkdir("ignore_folder")
+    testdir.run("mv", "test_exclude_folder.py", ignore_folder)
+
+    # Rename pyproject.toml ¯\_(ツ)_/¯
+    testdir.run("mv", "test_exclude_folder.pyproject.toml", "pyproject.toml")
+
+    result = testdir.runpytest("--black")
+    result.assert_outcomes(skipped=1, passed=0)
+
+
 def test_include(testdir):
     """Assert test is not skipped if path is included but not excluded
     """