Allow attrs kw_only arguments at any position (#8803)

Fixes #7489.

mypy/plugins/attrs.py

@@ -358,15 +358,13 @@ def _analyze_class(ctx: 'mypy.plugin.ClassDefContext',
     # Check the init args for correct default-ness.  Note: This has to be done after all the
     # attributes for all classes have been read, because subclasses can override parents.
     last_default = False
-    last_kw_only = False
 
     for i, attribute in enumerate(attributes):
         if not attribute.init:
             continue
 
         if attribute.kw_only:
             # Keyword-only attributes don't care whether they are default or not.
-            last_kw_only = True
             continue
 
         # If the issue comes from merging different classes, report it
@@ -377,11 +375,6 @@ def _analyze_class(ctx: 'mypy.plugin.ClassDefContext',
             ctx.api.fail(
                 "Non-default attributes not allowed after default attributes.",
                 context)
-        if last_kw_only:
-            ctx.api.fail(
-                "Non keyword-only attributes are not allowed after a keyword-only attribute.",
-                context
-            )
         last_default |= attribute.has_default
 
     return attributes
@@ -626,7 +619,18 @@ def _make_frozen(ctx: 'mypy.plugin.ClassDefContext', attributes: List[Attribute]
 def _add_init(ctx: 'mypy.plugin.ClassDefContext', attributes: List[Attribute],
               adder: 'MethodAdder') -> None:
     """Generate an __init__ method for the attributes and add it to the class."""
-    args = [attribute.argument(ctx) for attribute in attributes if attribute.init]
+    # Convert attributes to arguments with kw_only arguments at the  end of
+    # the argument list
+    pos_args = []
+    kw_only_args = []
+    for attribute in attributes:
+        if not attribute.init:
+            continue
+        if attribute.kw_only:
+            kw_only_args.append(attribute.argument(ctx))
+        else:
+            pos_args.append(attribute.argument(ctx))
+    args = pos_args + kw_only_args
     if all(
         # We use getattr rather than instance checks because the variable.type
         # might be wrapped into a Union or some other type, but even non-Any

test-data/unit/check-attr.test

@@ -1070,11 +1070,12 @@ class A:
      a = attr.ib(default=0)
 @attr.s
 class B(A):
-    b = attr.ib()  # E: Non keyword-only attributes are not allowed after a keyword-only attribute.
+    b = attr.ib()
 @attr.s
 class C:
     a = attr.ib(kw_only=True)
-    b = attr.ib(15)  # E: Non keyword-only attributes are not allowed after a keyword-only attribute.
+    b = attr.ib(15)
+
 [builtins fixtures/attr.pyi]
 
 [case testAttrsKwOnlyPy2]

test-data/unit/fine-grained.test

@@ -1023,31 +1023,6 @@ class A:
 ==
 main:2: error: Unsupported left operand type for < ("B")
 
-[case testAttrsUpdateKwOnly]
-[file a.py]
-import attr
-@attr.s(kw_only=True)
-class A:
-    a = attr.ib(15)   # type: int
-[file b.py]
-from a import A
-import attr
-@attr.s(kw_only=True)
-class B(A):
-    b = attr.ib("16")   # type: str
-
-[file b.py.2]
-from a import A
-import attr
-@attr.s()
-class B(A):
-    b = attr.ib("16")   # type: str
-B(b="foo", a=7)
-[builtins fixtures/attr.pyi]
-[out]
-==
-b.py:5: error: Non keyword-only attributes are not allowed after a keyword-only attribute.
-
 [case testAttrsUpdateBaseKwOnly]
 from b import B
 B(5)