Merge branch '405-nonexisting-files' into 'master'

Resolve "flake8 does not generate error when given a non-existent file on the command line"

Closes #405

See merge request pycqa/flake8!227

Author: sigmavirus24

src/flake8/checker.py

@@ -210,7 +210,6 @@ def should_create_file_checker(filename, argument):
                 filename, filename_patterns
             )
             is_stdin = filename == '-'
-            file_exists = os.path.exists(filename)
             # NOTE(sigmavirus24): If a user explicitly specifies something,
             # e.g, ``flake8 bin/script`` then we should run Flake8 against
             # that. Since should_create_file_checker looks to see if the
@@ -221,8 +220,7 @@ def should_create_file_checker(filename, argument):
             explicitly_provided = (not running_from_vcs and
                                    not running_from_diff and
                                    (argument == filename))
-            return ((file_exists and
-                     (explicitly_provided or matches_filename_patterns)) or
+            return ((explicitly_provided or matches_filename_patterns) or
                     is_stdin)
 
         checks = self.checks.to_dictionary()

tests/unit/test_file_checker.py

@@ -32,3 +32,14 @@ def test_repr(*args):
         'example.py', checks={}, options=object(),
     )
     assert repr(file_checker) == 'FileChecker for example.py'
+
+
+def test_nonexistent_file():
+    """Verify that checking non-existent file results in an error."""
+    c = checker.FileChecker("foobar.py", checks={}, options=object())
+
+    assert c.processor is None
+    assert not c.should_process
+    assert len(c.results) == 1
+    error = c.results[0]
+    assert error[0] == "E902"

tests/unit/test_file_processor.py

@@ -321,3 +321,8 @@ def test_log_token(token, log_string):
 def test_count_parentheses(current_count, token_text, expected):
     """Verify our arithmetic is correct."""
     assert processor.count_parentheses(current_count, token_text) == expected
+
+
+def test_nonexistent_file():
+    with pytest.raises(IOError):
+        processor.FileProcessor("foobar.py", options_from())