Allow type checkers to ignore specific error codes (#2153)

* Allow type: ignore error codes filtering

* Try to improve the wording for the spec

* Rephrase a bit of the spec

* Avoid specifying how whitespace after # type: ignore works

* Update conformance/tests/directives_type_ignore.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Update docs/spec/directives.rst

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Rerun the tests

* Change the error code to a random error code and allow the error to happen

* Update conformance/tests/directives_type_ignore.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

---------

Co-authored-by: Carl Meyer <carl@oddbird.net>

Author: davidhalter

conformance/results/mypy/directives_type_ignore.toml

@@ -5,11 +5,10 @@ Does not honor "# type: ignore" comment if comment includes additional text.
 output = """
 directives_type_ignore.py:11: error: Invalid "type: ignore" comment  [syntax]
 directives_type_ignore.py:11: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]
-directives_type_ignore.py:14: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]
-directives_type_ignore.py:14: note: Error code "assignment" not covered by "type: ignore" comment
+directives_type_ignore.py:16: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]
+directives_type_ignore.py:16: note: Error code "assignment" not covered by "type: ignore" comment
 """
 conformance_automated = "Fail"
 errors_diff = """
 Line 11: Unexpected errors ['directives_type_ignore.py:11: error: Invalid "type: ignore" comment  [syntax]', 'directives_type_ignore.py:11: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]']
-Line 14: Unexpected errors ['directives_type_ignore.py:14: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]']
 """

conformance/results/results.html

@@ -1198,9 +1198,9 @@ <h3>Python Type System Conformance Test Results</h3>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;directives_type_ignore</th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not honor "# type: ignore" comment if comment includes additional text.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not honor "# type: ignore" comment if comment includes additional text.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Treats `# type: ignore[error-code]` as only ignoring errors that match the error code `error-code`.</p></span></div></th>
+<th class="column col2 conformant">Pass</th>
+<th class="column col2 conformant">Pass</th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;directives_type_ignore_file1</th>
 <th class="column col2 conformant">Pass</th>

conformance/results/ty/directives_type_ignore.toml

@@ -1,11 +1,6 @@
-conformance_automated = "Fail"
-conformant = "Partial"
-notes = """
-Treats `# type: ignore[error-code]` as only ignoring errors that match the error code `error-code`.
-"""
+conformance_automated = "Pass"
 errors_diff = """
-Line 14: Unexpected errors ['directives_type_ignore.py:14:10: error[invalid-assignment] Object of type `Literal[""]` is not assignable to `int`']
 """
 output = """
-directives_type_ignore.py:14:10: error[invalid-assignment] Object of type `Literal[""]` is not assignable to `int`
+directives_type_ignore.py:16:10: error[invalid-assignment] Object of type `Literal[""]` is not assignable to `int`
 """

conformance/results/zuban/directives_type_ignore.toml

@@ -1,12 +1,7 @@
-conformant = "Partial"
-notes = """
-Does not honor "# type: ignore" comment if comment includes additional text.
-"""
-conformance_automated = "Fail"
+conformance_automated = "Pass"
 errors_diff = """
-Line 14: Unexpected errors ['directives_type_ignore.py:14: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]']
 """
 output = """
-directives_type_ignore.py:14: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]
-directives_type_ignore.py:14: note: Error code "assignment" not covered by "type: ignore" comment
+directives_type_ignore.py:16: error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]
+directives_type_ignore.py:16: note: Error code "assignment" not covered by "type: ignore" comment
 """

conformance/tests/directives_type_ignore.py

@@ -10,8 +10,10 @@
 # The following type violation should be suppressed.
 y: int = ""  # type: ignore - additional stuff
 
-# The following type violation should be suppressed.
-z: int = ""  # type: ignore[additional_stuff]
+# The following type violation may be suppressed, if the type checker
+# actually uses the code `an-empty-str-is-not-an-int` (unlikely!), or if
+# it treats unknown codes as blanket ignores.
+z: int = ""  # type: ignore[an-empty-str-is-not-an-int]  # E?
 
 # > In some cases, linting tools or other comments may be needed on the same
 # > line as a type comment. In these cases, the type comment should be before

docs/spec/directives.rst

@@ -73,6 +73,15 @@ other comments and linting markers:
 
   # type: ignore # <comment or other marker>
 
+The form ``# type: ignore[...]`` may be used to suppress only type errors with a
+given error code, though support for this is optional and may vary by type checker:
+
+- Given ``# type: ignore[my_code1]``, a type checker may ignore the error code
+  ``my_code1`` and choose to treat this form as equivalent to ``# type: ignore``.
+- Alternatively, given ``# type: ignore[my_code1]`` a type checker may suppress the
+  error only if the error cause matches the error code ``my_code1``.
+- A bare ``# type: ignore`` must always suppress all type errors.
+
 .. _`cast`:
 
 ``cast()``