Fix crash on star unpack in TypedDict (#16116)

Fixes #16107
Fixes #15891

I only vaguely remember why I added those context managers, it seemed to
me giving full TypedDict as context may cause false positives. But since
the current way causes crashes, let's just not do this (we will see if
there will be actual false positives).

mypy/checkexpr.py

@@ -813,8 +813,7 @@ def validate_star_typeddict_item(
         Note `result` and `always_present_keys` are updated in place. Return true if the
         expression `item_arg` may valid in `callee` TypedDict context.
         """
-        with self.chk.local_type_map(), self.msg.filter_errors():
-            inferred = get_proper_type(self.accept(item_arg, type_context=callee))
+        inferred = get_proper_type(self.accept(item_arg, type_context=callee))
         possible_tds = []
         if isinstance(inferred, TypedDictType):
             possible_tds = [inferred]

test-data/unit/check-typeddict.test

@@ -3224,3 +3224,15 @@ t2: Foo = {**y}  # E: Missing key "a" for TypedDict "Foo"
 t3: Foo = {**z}  # E: Missing key "a" for TypedDict "Foo"
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
+
+[case testTypedDictUnpackError]
+from typing import TypedDict
+
+class Foo(TypedDict):
+    a: int
+
+def foo(x: int) -> Foo: ...
+
+f: Foo = {**foo("no")}  # E: Argument 1 to "foo" has incompatible type "str"; expected "int"
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-typeddict.pyi]

test-data/unit/reports.test

@@ -69,6 +69,40 @@ def untyped_function():
   </packages>
 </coverage>
 
+[case testCoberturaStarUnpacking]
+# cmd: mypy --cobertura-xml-report build a.py
+[file a.py]
+from typing import TypedDict
+
+class MyDict(TypedDict):
+    a: int
+
+def foo(a: int) -> MyDict:
+    return {"a": a}
+md: MyDict = MyDict(**foo(42))
+[outfile build/cobertura.xml]
+<coverage timestamp="$TIMESTAMP" version="$VERSION" line-rate="0.8333" branch-rate="0">
+  <sources>
+    <source>$PWD</source>
+  </sources>
+  <packages>
+    <package complexity="1.0" name="a" branch-rate="0" line-rate="0.8333">
+      <classes>
+        <class complexity="1.0" filename="a.py" name="a.py" branch-rate="0" line-rate="0.8333">
+          <methods/>
+          <lines>
+            <line branch="false" hits="1" number="1" precision="precise"/>
+            <line branch="false" hits="1" number="3" precision="precise"/>
+            <line branch="false" hits="0" number="4" precision="any"/>
+            <line branch="false" hits="1" number="6" precision="precise"/>
+            <line branch="false" hits="1" number="7" precision="precise"/>
+            <line branch="false" hits="1" number="8" precision="precise"/>
+          </lines>
+        </class>
+      </classes>
+    </package>
+  </packages>
+</coverage>
 
 [case testAnyExprReportDivisionByZero]
 # cmd: mypy --any-exprs-report=out -c 'pass'