New analyser: Fix crash in plugins when star import blocks adding a symbol (#7136)

Fixes #7076

The fix is pretty straightforward. I also add a comment about `missing_names` being per-module, not per namespace.

Author: ilevkivskyi

mypy/newsemanal/semanal.py

@@ -201,6 +201,12 @@ class NewSemanticAnalyzer(NodeVisitor[None],
     # unbound names due to cyclic definitions and should not defer)?
     _final_iteration = False
     # These names couldn't be added to the symbol table due to incomplete deps.
+    # Note that missing names are per module, _not_ per namespace. This means that e.g.
+    # a missing name at global scope will block adding same name at a class scope.
+    # This should not affect correctness and is purely a performance issue,
+    # since it can cause unnecessary deferrals.
+    # Note that a star import adds a special name '*' to the set, this blocks
+    # adding _any_ names in the current file.
     missing_names = None  # type: Set[str]
     # Callbacks that will be called after semantic analysis to tweak things.
     patches = None  # type: List[Tuple[int, Callable[[], None]]]

mypy/plugins/attrs.py

@@ -212,7 +212,12 @@ def attr_class_maker_callback(ctx: 'mypy.plugin.ClassDefContext',
     if ctx.api.options.new_semantic_analyzer:
         # Check if attribute types are ready.
         for attr in attributes:
-            if info[attr.name].type is None and not ctx.api.final_iteration:
+            node = info.get(attr.name)
+            if node is None:
+                # This name is likely blocked by a star import. We don't need to defer because
+                # defer() is already called by mark_incomplete().
+                return
+            if node.type is None and not ctx.api.final_iteration:
                 ctx.api.defer()
                 return
 

mypy/plugins/dataclasses.py

@@ -213,7 +213,14 @@ def collect_attributes(self) -> List[DataclassAttribute]:
             if not isinstance(lhs, NameExpr):
                 continue
 
-            node = cls.info.names[lhs.name].node
+            sym = cls.info.names.get(lhs.name)
+            if sym is None:
+                # This name is likely blocked by a star import. We don't need to defer because
+                # defer() is already called by mark_incomplete().
+                assert ctx.api.options.new_semantic_analyzer
+                continue
+
+            node = sym.node
             if isinstance(node, PlaceholderNode):
                 # This node is not ready yet.
                 continue

test-data/unit/check-attr.test

@@ -1151,3 +1151,19 @@ class C:
 
 C(0).total = 1  # E: Property "total" defined in "C" is read-only
 [builtins fixtures/bool.pyi]
+
+[case testTypeInAttrDeferredStar]
+import lib
+[file lib.py]
+import attr
+from other import *
+
+@attr.s
+class C:
+    total = attr.ib(type=int)
+
+C()  # E: Too few arguments for "C"
+C('no')  # E: Argument 1 to "C" has incompatible type "str"; expected "int"
+[file other.py]
+import lib
+[builtins fixtures/bool.pyi]

test-data/unit/check-dataclasses.test

@@ -665,3 +665,19 @@ def func() -> int: ...
 c: C
 c.x = 1  # E: Property "x" defined in "C" is read-only
 [builtins fixtures/bool.pyi]
+
+[case testTypeInDataclassDeferredStar]
+import lib
+[file lib.py]
+from dataclasses import dataclass
+from other import *
+
+@dataclass
+class C:
+    total: int
+
+C()  # E: Too few arguments for "C"
+C('no')  # E: Argument 1 to "C" has incompatible type "str"; expected "int"
+[file other.py]
+import lib
+[builtins fixtures/bool.pyi]