Deduplicate error codes for ignore-without-code

docs/source/error_code_list2.rst

@@ -257,6 +257,8 @@ except that attempting to invoke an undefined method (e.g. ``__len__``) results
 while attempting to evaluate an object in boolean context without a concrete implementation results in a truthy value.
 
 
+.. _ignore-without-code:
+
 Check that ``# type: ignore`` include an error code [ignore-without-code]
 -------------------------------------------------------------------------
 
@@ -280,7 +282,7 @@ Example:
     # - the expected error 'assignment', and
     # - the unexpected error 'attr-defined'
     # are silenced.
-    # Error: "type: ignore" comment without error code (currently ignored: [attr-defined])
+    # Error: "type: ignore" comment without error code (use "type: ignore[attr-defined]" instead)
     f.nme = 42  # type: ignore
 
     # This line warns correctly about the typo in the attribute name

docs/source/error_codes.rst

@@ -31,6 +31,10 @@ or config `show_error_codes = True` to display error codes. Error codes are show
    $ mypy --show-error-codes prog.py
    prog.py:1: error: "str" has no attribute "trim"  [attr-defined]
 
+It's also possible to require error codes for ``type: ignore`` comments.
+See :ref:`ignore-without-code<ignore-without-code>` for more information.
+
+
 .. _silence-error-codes:
 
 Silencing errors based on error codes

mypy/errors.py

@@ -532,9 +532,9 @@ def generate_ignore_without_code_errors(self,
                 continue
 
             codes_hint = ''
-            ignored_codes = used_ignored_lines[line]
+            ignored_codes = sorted(set(used_ignored_lines[line]))
             if ignored_codes:
-                codes_hint = f' (currently ignored: [{", ".join(ignored_codes)}])'
+                codes_hint = f' (use "type: ignore[{", ".join(ignored_codes)}]" instead)'
 
             message = f'"type: ignore" comment without error code{codes_hint}'
             # Don't use report since add_error_info will ignore the error!

test-data/unit/check-errorcodes.test

@@ -148,7 +148,7 @@ x # type: ignore[name-defined, attr-defined] # E: Unused "type: ignore[attr-defi
 [case testErrorCodeMissingWhenRequired]
 # flags: --enable-error-code ignore-without-code
 "x" # type: ignore # E: "type: ignore" comment without error code  [ignore-without-code]
-y # type: ignore # E: "type: ignore" comment without error code (currently ignored: [name-defined])  [ignore-without-code]
+y # type: ignore # E: "type: ignore" comment without error code (use "type: ignore[name-defined]" instead)  [ignore-without-code]
 z # type: ignore[name-defined]
 "a" # type: ignore[ignore-without-code]
 
@@ -164,6 +164,18 @@ z # type: ignore[ignore-without-code] # E: Unused "type: ignore" comment # E: Na
 x
 y # type: ignore  # ignore the lack of error code since we're ignore the whole file
 
+[case testErrorCodeMissingMultiple]
+# flags: --enable-error-code ignore-without-code --python-version 3.7
+from __future__ import annotations
+class A:
+    attr: int
+    def func(self, var: int) -> A | None: ...
+
+a: A | None
+# 'union-attr' should only be listed once (instead of twice) and list should be sorted
+a.func("invalid string").attr  # type: ignore  # E: "type: ignore" comment without error code (use "type: ignore[arg-type, union-attr]" instead)  [ignore-without-code]
+[builtins fixtures/tuple.pyi]
+
 [case testErrorCodeIgnoreWithExtraSpace]
 x  # type: ignore   [name-defined]
 x2 # type: ignore   [ name-defined ]