Add --stdin-display-name to modify report output

docs/source/user/options.rst

@@ -192,6 +192,30 @@
             another-example*.py
 
 
+.. option:: --stdin-display-name=<display_name>
+
+    Provide the name to use to report warnings and errors from code on stdin.
+
+    Instead of reporting an error as something like:
+
+    .. code::
+
+        stdin:82:73 E501 line too long
+
+    You can specify this option to have it report whatever value you want
+    instead of stdin.
+
+    This defaults to: ``stdin``
+
+    Command-line example:
+
+    .. prompt:: bash
+
+        cat file.py | flake8 --stdin-display-name=file.py -
+
+    This **can not** be specified in config files.
+
+
 .. option:: --format=<format>
 
     Select the formatter used to display errors to the user.

flake8/main/cli.py

@@ -86,6 +86,13 @@ def register_default_options(option_manager):
              'separated list. (Default: %default)',
     )
 
+    add_option(
+        '--stdin-display-name', default='stdin',
+        help='The name used when reporting errors from code passed via stdin.'
+             ' This is useful for editors piping the file contents to flake8.'
+             ' (Default: %default)',
+    )
+
     # TODO(sigmavirus24): Figure out --first/--repeat
 
     add_option(

flake8/style_guide.py

@@ -237,6 +237,8 @@ class StyleGuide(object):
         """Handle an error reported by a check."""
         error = Error(code, filename, line_number, column_number, text,
                       physical_line)
+        if error.filename is None or error.filename == '-':
+            error = error._replace(filename=self.options.stdin_display_name)
         error_is_selected = (self.should_report_error(error.code) is
                              Decision.Selected)
         is_not_inline_ignored = self.is_inline_ignored(error) is False