document, and add a new test

Author: wyattscarpenter

docs/source/command_line.rst

@@ -799,6 +799,24 @@ of the above sections.
         x = 'a string'
         x.trim()  # error: "str" has no attribute "trim"  [attr-defined]
 
+.. option:: --enable-all-error-codes
+
+    This flag enables all of the error codes for mypy,
+    including the optional ones that are off by default.
+    See :ref:`error-codes` for more information.
+
+    This flag will override disabled error codes from the
+    :option:`--disable-error-code <mypy --disable-error-code>` flag.
+
+    Note that future releases of mypy will likely introduce more error codes,
+    so the effective behavior of this flag will change from release to release.
+
+    While often useful, this flag will enable **all** error codes,
+    including those that may be experimental, wrongheaded, or contradictory.
+
+    It is not the same as enabling all checks that mypy could perform;
+    for example, :option:`--strict-bytes` is not enabled by this flag.
+
 .. _configuring-error-messages:
 
 Configuring error messages

docs/source/config_file.rst

@@ -761,6 +761,15 @@ section of the command line docs.
 
     Note: This option will override disabled error codes from the disable_error_code option.
 
+.. confval:: enable_all_error_codes
+
+    :type: boolean
+    :default: False
+
+    Enables all mypy error codes.
+
+    Note: This option will override disabled error codes from the disable_error_code option.
+
 .. confval:: extra_checks
 
    :type: boolean

test-data/unit/check-flags.test

@@ -2494,7 +2494,7 @@ class Child(Parent):
 # (For example, if all the errors expected by testSpotCheckErrorCodeAll get turned on by default, then
 #  the testSpotCheckErrorCodeAll test would fail to guarantee the enablement of any additional errors!
 #  (hint: if that does happen, breaking this test, then consider changing these two tests to pick *different*,
-#   not-enabled-by-default, error codes.))
+#   not-enabled-by-default, error codes. Also, testSpotCheckEnableAllErrorCodesConfig.))
 from typing_extensions import override
 
 class Parent:
@@ -2512,3 +2512,25 @@ class Child(Parent):
     def g(self, y: int) -> None: #type: ignore
         pass
 [builtins fixtures/tuple-simple.pyi]
+
+[case testSpotCheckEnableAllErrorCodesConfig]
+# flags: --config-file tmp/mypy.ini
+# This test just makes sure that the user can still countermand
+# enable_all_error_codes on a more-specific level.
+import tests.foo
+import bar
+[file bar.py]
+def foo() -> int: ...
+if foo: ...  # E: Function "foo" could always be true in boolean context
+42 + "no"  # type: ignore  # E: "type: ignore" comment without error code (consider "type: ignore[operator]" instead)
+[file tests/__init__.py]
+[file tests/foo.py]
+def foo() -> int: ...
+if foo: ...  # E: Function "foo" could always be true in boolean context
+42 + "no"  # type: ignore
+[file mypy.ini]
+\[mypy]
+enable_all_error_codes = True
+
+\[mypy-tests.*]
+disable_error_code = ignore-without-code