Add indent-size option

src/flake8/defaults.py

@@ -15,6 +15,7 @@ EXCLUDE = (
 IGNORE = ("E121", "E123", "E126", "E226", "E24", "E704", "W503", "W504")
 SELECT = ("E", "F", "W", "C90")
 MAX_LINE_LENGTH = 79
+INDENT_SIZE = 4
 
 TRUTHY_VALUES = {"true", "1", "t"}
 

src/flake8/main/options.py

@@ -105,6 +105,7 @@ def register_default_options(option_manager):
     - ``--per-file-ignores``
     - ``--max-line-length``
     - ``--max-doc-length``
+    - ``--indent-size``
     - ``--select``
     - ``--disable-noqa``
     - ``--show-source``
@@ -254,6 +255,14 @@ def register_default_options(option_manager):
         help="Maximum allowed doc line length for the entirety of this run. "
         "(Default: %(default)s)",
     )
+    add_option(
+        "--indent-size",
+        type=int,
+        metavar="n",
+        default=defaults.INDENT_SIZE,
+        parse_from_config=True,
+        help="Number of spaces used for indentation (Default: %default)",
+    )
 
     add_option(
         "--select",

src/flake8/processor.py

@@ -83,6 +83,8 @@ class FileProcessor(object):
         self.indent_char = None  # type: Optional[str]
         #: Current level of indentation
         self.indent_level = 0
+        #: Number of spaces used for indentation
+        self.indent_size = options.indent_size
         #: Line number in the file
         self.line_number = 0
         #: Current logical line