Make "deprecated" Note a standard Error, disabled by default (#18192)

While working on the relase of mypy 1.14 we noticed a large number of
notes for deprecated. Speaking with Jukka, he suggested we make this
disabled by default. And if it's disabled by default, having it as a
note is not as useful. We also don't have many stand alone notes. Most
notes are "attached" with an error.

This PR makes the deprecated error disabled by default and by default
reports it as error when enabled. `--report-deprecated-as-note` can
be used to report them as notes instead.

Author: svalentin

docs/source/command_line.rst

@@ -541,12 +541,12 @@ potentially problematic or redundant in some way.
 
         This limitation will be removed in future releases of mypy.
 
-.. option:: --report-deprecated-as-error
+.. option:: --report-deprecated-as-note
 
-    By default, mypy emits notes if your code imports or uses deprecated
-    features.    This flag converts such notes to errors, causing mypy to
-    eventually finish with a non-zero exit code.  Features are considered
-    deprecated when decorated with ``warnings.deprecated``.
+    If error code ``deprecated`` is enabled, mypy emits errors if your code
+    imports or uses deprecated features. This flag converts such errors to
+    notes, causing mypy to eventually finish with a zero exit code. Features
+    are considered deprecated when decorated with ``warnings.deprecated``.
 
 .. _miscellaneous-strictness-flags:
 

docs/source/error_code_list2.rst

@@ -236,13 +236,13 @@ incorrect control flow or conditional checks that are accidentally always true o
 Check that imported or used feature is deprecated [deprecated]
 --------------------------------------------------------------
 
-By default, mypy generates a note if your code imports a deprecated feature explicitly with a
+If you use :option:`--enable-error-code deprecated <mypy --enable-error-code>`,
+mypy generates an error if your code imports a deprecated feature explicitly with a
 ``from mod import depr`` statement or uses a deprecated feature imported otherwise or defined
 locally.  Features are considered deprecated when decorated with ``warnings.deprecated``, as
-specified in `PEP 702 <https://peps.python.org/pep-0702>`_.  You can silence single notes via
-``# type: ignore[deprecated]`` or turn off this check completely via ``--disable-error-code=deprecated``.
-Use the :option:`--report-deprecated-as-error <mypy --report-deprecated-as-error>` option for
-more strictness, which turns all such notes into errors.
+specified in `PEP 702 <https://peps.python.org/pep-0702>`_.
+Use the :option:`--report-deprecated-as-note <mypy --report-deprecated-as-note>` option to
+turn all such errors into notes.
 
 .. note::
 

mypy/checker.py

@@ -7696,7 +7696,7 @@ def warn_deprecated(self, node: SymbolNode | None, context: Context) -> None:
             and ((deprecated := node.deprecated) is not None)
             and not self.is_typeshed_stub
         ):
-            warn = self.msg.fail if self.options.report_deprecated_as_error else self.msg.note
+            warn = self.msg.note if self.options.report_deprecated_as_note else self.msg.fail
             warn(deprecated, context, code=codes.DEPRECATED)
 
 

mypy/errorcodes.py

@@ -308,6 +308,7 @@ def __hash__(self) -> int:
     "deprecated",
     "Warn when importing or using deprecated (overloaded) functions, methods or classes",
     "General",
+    default_enabled=False,
 )
 
 # This copy will not include any error codes defined later in the plugins.

mypy/main.py

@@ -810,10 +810,10 @@ def add_invertible_flag(
         group=lint_group,
     )
     add_invertible_flag(
-        "--report-deprecated-as-error",
+        "--report-deprecated-as-note",
         default=False,
         strict_flag=False,
-        help="Report importing or using deprecated features as errors instead of notes",
+        help="Report importing or using deprecated features as notes instead of errors",
         group=lint_group,
     )
 

mypy/options.py

@@ -177,7 +177,7 @@ def __init__(self) -> None:
         self.warn_return_any = False
 
         # Report importing or using deprecated features as errors instead of notes.
-        self.report_deprecated_as_error = False
+        self.report_deprecated_as_note = False
 
         # Warn about unused '# type: ignore' comments
         self.warn_unused_ignores = False

mypy/typeanal.py

@@ -790,7 +790,7 @@ def check_and_warn_deprecated(self, info: TypeInfo, ctx: Context) -> None:
                 if isinstance(imp, ImportFrom) and any(info.name == n[0] for n in imp.names):
                     break
             else:
-                warn = self.fail if self.options.report_deprecated_as_error else self.note
+                warn = self.note if self.options.report_deprecated_as_note else self.fail
                 warn(deprecated, ctx, code=codes.DEPRECATED)
 
     def analyze_type_with_type_info(