From e50c043a4f0fc642ce8384eb80cf32e74e526541 Mon Sep 17 00:00:00 2001
From: Matthew Hoffman <matthew@protopia.ai>
Date: Sun, 18 Jun 2023 17:05:32 -0700
Subject: [PATCH] Infer function parameter types using annotations

Fixes https://github.com/pylint-dev/pylint/issues/4813 & https://github.com/pylint-dev/pylint/issues/8781
---
 astroid/inference.py    | 24 ++++++++++++++++++++++--
 tests/test_inference.py | 18 ++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/astroid/inference.py b/astroid/inference.py
index 6dcfa49f1b..bf61a6377f 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -1168,10 +1168,30 @@ def infer_assign(
     assign node.
     """
     if isinstance(self.parent, nodes.AugAssign):
-        return self.parent.infer(context)
+        yield from self.parent.infer(context)
+        return
 
     stmts = list(self.assigned_stmts(context=context))
-    return bases._infer_stmts(stmts, context)
+    yield from bases._infer_stmts(stmts, context)
+
+    # Infer function parameter types using their annotations, if present.
+    if (
+        isinstance(self, nodes.AssignName)
+        and isinstance(self.parent, nodes.Arguments)
+        and self.parent.args is not None
+    ):
+        try:
+            annotation_index = self.parent.args.index(self)
+        except ValueError:
+            annotation_index = None
+
+        if (
+            annotation_index is not None
+            and (annotation := self.parent.annotations[annotation_index]) is not None
+        ):
+            for annotation_result in annotation.infer(context=context):
+                if isinstance(annotation_result, nodes.ClassDef):
+                    yield bases.Instance(annotation_result)
 
 
 nodes.AssignName._infer = infer_assign
diff --git a/tests/test_inference.py b/tests/test_inference.py
index 6760f9c91b..92521091e7 100644
--- a/tests/test_inference.py
+++ b/tests/test_inference.py
@@ -4488,6 +4488,24 @@ def test_uninferable_type_subscript(self) -> None:
         with self.assertRaises(InferenceError):
             _ = next(node.infer())
 
+    def test_infer_parameters_from_type_hints(self) -> None:
+        node = extract_node(
+            """
+        class Logger:
+            def info(self, msg: str) -> None:
+                ...
+
+        class MyClassThatLogs:
+            def __init__(self, logger: Logger) -> None:
+                self.logger = logger
+
+        my_class_that_logs = MyClassThatLogs(Logger())
+        my_class_that_logs.logger
+        """
+        )
+        inferred = list(node.infer())
+        assert isinstance(inferred[1], Instance)
+
 
 class GetattrTest(unittest.TestCase):
     def test_yes_when_unknown(self) -> None: