clarify evolve of _what_

Author: ikonst

mypy/plugins/attrs.py

@@ -8,6 +8,7 @@
 import mypy.plugin  # To avoid circular imports.
 from mypy.checker import TypeChecker
 from mypy.exprtotype import TypeTranslationError, expr_to_unanalyzed_type
+from mypy.messages import format_type_bare
 from mypy.nodes import (
     ARG_NAMED,
     ARG_NAMED_OPT,
@@ -926,13 +927,14 @@ def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> Callabl
     inst_type = get_proper_type(inst_type)
     if isinstance(inst_type, AnyType):
         return ctx.default_signature
+    inst_type_str = format_type_bare(inst_type)
 
     # In practice, we're taking the initializer generated by _add_init and tweaking it
     # so that (a) its arguments are kw-only & optional, and (b) its return type is the instance's.
     attrs_init_type = _get_attrs_init_type(inst_type)
     if not attrs_init_type:
         ctx.api.fail(
-            f'Argument 1 to "evolve" has incompatible type "{inst_type}"; expected an attrs class',
+            f'Argument 1 to "evolve" has incompatible type "{inst_type_str}"; expected an attrs class',
             ctx.context,
         )
         return ctx.default_signature
@@ -941,5 +943,5 @@ def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> Callabl
         arg_names=["inst"] + attrs_init_type.arg_names[1:],
         arg_kinds=[ARG_POS] + [ARG_NAMED_OPT for _ in attrs_init_type.arg_kinds[1:]],
         ret_type=inst_type,
-        name=ctx.default_signature.name,
+        name=f"{ctx.default_signature.name} of {inst_type_str}",
     )

test-data/unit/check-attr.test

@@ -1889,12 +1889,12 @@ class C:
 c = C(name='foo', b=Derived())
 c = attr.evolve(c)
 c = attr.evolve(c, name='foo')
-c = attr.evolve(c, 'foo')  # E: Too many positional arguments for "evolve"
+c = attr.evolve(c, 'foo')  # E: Too many positional arguments for "evolve" of "C"
 c = attr.evolve(c, b=Derived())
 c = attr.evolve(c, b=Base())
-c = attr.evolve(c, b=Other())  # E: Argument "b" to "evolve" has incompatible type "Other"; expected "Base"
-c = attr.evolve(c, name=42)  # E: Argument "name" to "evolve" has incompatible type "int"; expected "str"
-c = attr.evolve(c, foobar=42)  # E: Unexpected keyword argument "foobar" for "evolve"
+c = attr.evolve(c, b=Other())  # E: Argument "b" to "evolve" of "C" has incompatible type "Other"; expected "Base"
+c = attr.evolve(c, name=42)  # E: Argument "name" to "evolve" of "C" has incompatible type "int"; expected "str"
+c = attr.evolve(c, foobar=42)  # E: Unexpected keyword argument "foobar" for "evolve" of "C"
 
 # test passing instance as 'inst' kw
 c = attr.evolve(inst=c, name='foo')
@@ -1907,7 +1907,7 @@ def f() -> C:
 c = attr.evolve(f(), name='foo')
 
 # test 'inst' arg type check
-attr.evolve(42, name='foo')  # E: Argument 1 to "evolve" has incompatible type "Literal[42]?"; expected an attrs class
+attr.evolve(42, name='foo')  # E: Argument 1 to "evolve" has incompatible type "int"; expected an attrs class
 attr.evolve(None, name='foo')  # E: Argument 1 to "evolve" has incompatible type "None"; expected an attrs class
 
 # test that all bets are off for 'Any'
@@ -1931,13 +1931,13 @@ class C:
 c = C(name='foo')
 
 c = attr.assoc(c, name='test')
-c = attr.assoc(c, name=42)  # E: Argument "name" to "assoc" has incompatible type "int"; expected "str"
+c = attr.assoc(c, name=42)  # E: Argument "name" to "assoc" of "C" has incompatible type "int"; expected "str"
 
 c = attrs.evolve(c, name='test')
-c = attrs.evolve(c, name=42)  # E: Argument "name" to "evolve" has incompatible type "int"; expected "str"
+c = attrs.evolve(c, name=42)  # E: Argument "name" to "evolve" of "C" has incompatible type "int"; expected "str"
 
 c = attrs.assoc(c, name='test')
-c = attrs.assoc(c, name=42)  # E: Argument "name" to "assoc" has incompatible type "int"; expected "str"
+c = attrs.assoc(c, name=42)  # E: Argument "name" to "assoc" of "C" has incompatible type "int"; expected "str"
 
 [builtins fixtures/attr.pyi]
 [typing fixtures/typing-medium.pyi]