Add back support for warn_unused_configs (#20801)

ilevkivskyi · web-flow · commit d3de4a4b4b7b · 2026-02-17T16:10:26.000Z
Fixes #7998 This was disabled in incremental mode (i.e. almost always, since this is now the default), because we didn't clone options for suppressed dependencies, but now because we are doing this (for the purpose of fixing other issues), there is no reason to keep this disabled (IMO this is a nice feature to keep your config clean). Few more things here: * I moved the logic inside `build.build()`, first it is wrong to show this warning in case of blocking errors (since we may not processed all files yet), second it is easier to test. * I am now using more standard message formatting `path: note: ...` * I am updating couple comments I forgot to update in previous PRs (sorry)
diff --git a/mypy/build.py b/mypy/build.py
@@ -131,7 +131,7 @@
     from mypy.report import Reports  # Avoid unconditional slow import
 
 from mypy import errorcodes as codes
-from mypy.config_parser import parse_mypy_comments
+from mypy.config_parser import get_config_module_names, parse_mypy_comments
 from mypy.fixup import fixup_module
 from mypy.freetree import free_tree
 from mypy.fscache import FileSystemCache
@@ -481,6 +481,7 @@ def build_inner(
             dump_timing_stats(options.timing_stats, graph)
         if options.line_checking_stats is not None:
             dump_line_checking_stats(options.line_checking_stats, graph)
+        warn_unused_configs(options, flush_errors)
         return BuildResult(manager, graph)
     finally:
         t0 = time.time()
@@ -505,6 +506,19 @@ def build_inner(
             record_missing_stub_packages(options.cache_dir, manager.missing_stub_packages)
 
 
+def warn_unused_configs(
+    options: Options, flush_errors: Callable[[str | None, list[str], bool], None]
+) -> None:
+    if options.warn_unused_configs and options.unused_configs and not options.non_interactive:
+        unused = get_config_module_names(
+            options.config_file,
+            [glob for glob in options.per_module_options.keys() if glob in options.unused_configs],
+        )
+        flush_errors(
+            None, ["{}: note: unused section(s): {}".format(options.config_file, unused)], False
+        )
+
+
 def default_data_dir() -> str:
     """Returns directory containing typeshed directory."""
     return os.path.dirname(__file__)
@@ -3789,7 +3803,7 @@ def load_graph(
                 manager.missing_modules[dep] = SuppressionReason.NOT_FOUND
                 # TODO: for now we skip this in the daemon as a performance optimization.
                 # This however creates a correctness issue, see #7777 and State.is_fresh().
-                if not manager.use_fine_grained_cache():
+                if not manager.use_fine_grained_cache() or manager.options.warn_unused_configs:
                     manager.import_options[dep] = manager.options.clone_for_module(
                         dep
                     ).dep_import_options()
@@ -3839,8 +3853,8 @@ def load_graph(
                     graph[newst.id] = newst
                     new.append(newst)
     # There are two things we need to do after the initial load loop. One is up-suppress
-    # modules that are back in graph. We need to do this after the loop to cover an edge
-    # case where a namespace package ancestor is shared by a typed and an untyped package.
+    # modules that are back in graph. We need to do this after the loop to cover edge cases
+    # like where a namespace package ancestor is shared by a typed and an untyped package.
     for st in graph.values():
         for dep in st.suppressed.copy():
             if dep in graph:
diff --git a/mypy/ipc.py b/mypy/ipc.py
@@ -53,9 +53,8 @@ class IPCBase:
     This contains logic shared between the client and server, such as reading
     and writing.
     We want to be able to send multiple "messages" over a single connection and
-    to be able to separate the messages. We do this by encoding the messages
-    in an alphabet that does not contain spaces, then adding a space for
-    separation. The last framed message is also followed by a space.
+    to be able to separate the messages. We do this by prefixing each message
+    with its size in a fixed format.
     """
 
     connection: _IPCHandle
diff --git a/mypy/main.py b/mypy/main.py
@@ -23,12 +23,7 @@
     sys.exit(2)
 
 from mypy import build, defaults, state, util
-from mypy.config_parser import (
-    get_config_module_names,
-    parse_config_file,
-    parse_version,
-    validate_package_allow_list,
-)
+from mypy.config_parser import parse_config_file, parse_version, validate_package_allow_list
 from mypy.defaults import RECURSION_LIMIT
 from mypy.error_formatter import OUTPUT_CHOICES
 from mypy.errors import CompileError
@@ -221,26 +216,6 @@ def flush_errors(filename: str | None, new_messages: list[str], serious: bool) -
         blockers = True
         if not e.use_stdout:
             serious = True
-    if (
-        options.warn_unused_configs
-        and options.unused_configs
-        and not options.incremental
-        and not options.non_interactive
-    ):
-        print(
-            "Warning: unused section(s) in {}: {}".format(
-                options.config_file,
-                get_config_module_names(
-                    options.config_file,
-                    [
-                        glob
-                        for glob in options.per_module_options.keys()
-                        if glob in options.unused_configs
-                    ],
-                ),
-            ),
-            file=stderr,
-        )
     maybe_write_junit_xml(time.time() - t0, serious, messages, messages_by_file, options)
     return res, messages, blockers
 
diff --git a/test-data/unit/check-incremental.test b/test-data/unit/check-incremental.test
@@ -7929,6 +7929,58 @@ from a import b  # type: ignore[attr-defined]
 main:2: error: Unused "type: ignore" comment
 [out2]
 
+[case testConfigWarnUnusedSectionIncremental]
+# flags: --config-file=tmp/mypy.ini
+import m
+[file m.py]
+import a
+[file m.py.2]
+import a  # touch
+[file a.py]
+import foo  # type: ignore
+[file mypy.ini]
+\[mypy]
+warn_unused_configs = true
+\[mypy-bar]
+\[mypy-foo]
+[file mypy.ini.3]
+\[mypy]
+warn_unused_configs = true
+\[mypy-foo]
+[out]
+tmp/mypy.ini: note: unused section(s): [mypy-bar]
+[out2]
+tmp/mypy.ini: note: unused section(s): [mypy-bar]
+[out3]
+
+[case testConfigWarnUnusedSectionIncrementalTOML]
+# flags: --config-file tmp/pyproject.toml
+import m
+[file m.py]
+import a
+[file m.py.2]
+import a  # touch
+[file a.py]
+import foo  # type: ignore
+[file pyproject.toml]
+\[tool.mypy]
+warn_unused_configs = true
+\[[tool.mypy.overrides]]
+module = "bar"
+\[[tool.mypy.overrides]]
+module = "foo"
+warn_unreachable = true
+[file pyproject.toml.3]
+\[tool.mypy]
+warn_unused_configs = true
+\[[tool.mypy.overrides]]
+module = "foo"
+[out]
+tmp/pyproject.toml: note: unused section(s): module = ['bar']
+[out2]
+tmp/pyproject.toml: note: unused section(s): module = ['bar']
+[out3]
+
 [case testAddedMissingModuleSkip]
 # flags: --follow-imports=skip
 import mod
diff --git a/test-data/unit/cmdline.test b/test-data/unit/cmdline.test
@@ -535,7 +535,6 @@ variable has type "bytes")
 [file mypy.ini]
 \[mypy]
 warn_unused_configs = True
-incremental = False
 \[mypy-bar]
 \[mypy-foo]
 \[mypy-baz.*]
@@ -555,7 +554,7 @@ incremental = False
 [file spam/__init__.py]
 [file spam/eggs.py]
 [out]
-Warning: unused section(s) in mypy.ini: [mypy-bar], [mypy-baz.*], [mypy-emarg.*], [mypy-emarg.hatch], [mypy-a.*.c], [mypy-a.x.b]
+mypy.ini: note: unused section(s): [mypy-bar], [mypy-baz.*], [mypy-emarg.*], [mypy-emarg.hatch], [mypy-a.*.c], [mypy-a.x.b]
 == Return code: 0
 
 [case testPackageRootEmpty]
