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carbon-lang/toolchain/check/testdata/class/self/fail_self.carbon
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Chandler Carruthandjosh11b 7871237c15 Move self to the explicit () parameter list (proposal #7016) (#7272) 
Implements proposal #7016: `self` moves from the deduced implicit list
(`fn F[self: Self]()`) to the front of the explicit list. Its type may
be written explicitly (`fn F(self: Self)`) or omitted, in which case it
defaults to `Self` (`fn F(self)`, `fn F(ref self)`); `self` in the
implicit list is rejected.

Throughout checking, `self` is modeled as the first explicit parameter.
Because a method is just a function whose first parameter is `self`, it
can also be called as an ordinary function with the receiver passed
explicitly (`Type.M(obj, ...)`), not only as `obj.M(...)`. A new
`SemIR::CallArgParamPatterns` helper chooses the parameters matched
against the explicit arguments, excluding a leading `self` only when it
is supplied as a method-call receiver; arity checking, conversion, and
generic deduction use it. The resulting SemIR and lowering are
unchanged: `self` is still `call_param0`, and witnesses, thunks, and
vtables are unaffected.

An omitted `self` type is parsed as a `SelfBindingPattern` node with no
type expression; checking synthesizes the `Self` type so it behaves
exactly like `self: Self`. However, the exact spelling used must match
between a forward declaration and a definition, following #3763's rules
around declaration matching.

Generated functions, thunks, and C++ interop import/export build `self`
as the first explicit parameter, and the `self`-type override (e.g.
Derived->Base for a virtual override) applies to the explicit `self`.
Placement is validated by new diagnostics: `SelfInImplicitParamList`,
`SelfNotFirstParam`, and `SelfOutsideParamList`. The benchmark source
generator and the documentation adopt the `(self)` shorthand; the
prelude, the examples, and the test data are migrated in the following
commits.

Assisted-by: Claude Code with Claude Opus 4.7

---------

Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
2026-06-10 15:30:43 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/convert.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/class/self/fail_self.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/class/self/fail_self.carbon
// --- fail_self_implicit_list.carbon
library "[[@TEST_NAME]]";
// `self` is not permitted in the implicit parameter list, regardless of how
// its type is spelled (explicit `Self`, an arbitrary type, or omitted).
class Class {
// CHECK:STDERR: fail_self_implicit_list.carbon:[[@LINE+4]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn F[self: Self]();
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
fn F[self: Self]();
// CHECK:STDERR: fail_self_implicit_list.carbon:[[@LINE+4]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn G[self: Class]();
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
fn G[self: Class]();
// CHECK:STDERR: fail_self_implicit_list.carbon:[[@LINE+4]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn H[self]();
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn H[self]();
// CHECK:STDERR: fail_self_implicit_list.carbon:[[@LINE+4]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn I[ref self: Self]();
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR:
fn I[ref self: Self]();
// CHECK:STDERR: fail_self_implicit_list.carbon:[[@LINE+4]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn J[ref self]();
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR:
fn J[ref self]();
}
// --- fail_self_outside_class.carbon
library "[[@TEST_NAME]]";
// `self` outside any class scope has no `Self` to default to.
// CHECK:STDERR: fail_self_outside_class.carbon:[[@LINE+4]]:6: error: name `Self` not found [NameNotFound]
// CHECK:STDERR: fn F(self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn F(self);
// `ref self` is similarly invalid at file scope.
// CHECK:STDERR: fail_self_outside_class.carbon:[[@LINE+4]]:6: error: name `Self` not found [NameNotFound]
// CHECK:STDERR: fn G(ref self);
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR:
fn G(ref self);
// --- fail_self_repeated.carbon
library "[[@TEST_NAME]]";
class Class {
// Repeating `self` within a single parameter list is rejected.
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:14: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn F(self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn F(self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn F(self, self);
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:20: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn G(self: Self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn G(self: Self, self);
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
fn G(self: Self, self);
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:14: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn H(self, self: Self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn H(self, self: Self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn H(self, self: Self);
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:18: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn I(ref self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn I(ref self, self);
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR:
fn I(ref self, self);
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:24: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn J(ref self: Self, self: Self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn J(ref self: Self, self: Self);
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR:
fn J(ref self: Self, self: Self);
// `self` in both lists, even just once each, is rejected: the implicit
// occurrence is wrong, and the explicit one becomes a duplicate.
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+11]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn K[self](self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:14: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn K[self](self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn K[self](self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn K[self](self);
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+11]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn L[self: Self](self);
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:20: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn L[self: Self](self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn L[self: Self](self);
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
fn L[self: Self](self);
// Duplicates within the implicit list and across both lists.
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+15]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn M[self, self]();
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+11]]:14: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn M[self, self]();
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:14: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn M[self, self]();
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn M[self, self]();
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn M[self, self]();
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+29]]:8: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+25]]:14: error: `self` must be declared in the explicit parameter list [SelfInImplicitParamList]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+21]]:14: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+18]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+14]]:20: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+11]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+7]]:26: error: duplicate name `self` being declared in the same scope [NameDeclDuplicate]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_self_repeated.carbon:[[@LINE+4]]:8: note: name is previously declared here [NameDeclPrevious]
// CHECK:STDERR: fn N[self, self](self, self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
fn N[self, self](self, self);
}
// --- fail_var_self.carbon
library "[[@TEST_NAME]]";
class Class {
fn F();
}
fn Class.F() {
// `var self` is only valid as the receiver of a method, not as a local
// variable.
// CHECK:STDERR: fail_var_self.carbon:[[@LINE+4]]:14: error: `self` can only be declared in a parameter list [SelfOutsideParamList]
// CHECK:STDERR: var unused self: Self;
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
var unused self: Self;
}
// --- fail_self_wrong_type.carbon
library "[[@TEST_NAME]]";
// The receiver's type can be any type, not just the enclosing class. Here `self`
// has a type that differs from the class the method is declared in, which is
// diagnosed when the method is called with a receiver of the class's type.
class Class {}
class WrongSelf {
fn F(self: Class);
}
fn CallWrongSelf(ws: WrongSelf) {
// CHECK:STDERR: fail_self_wrong_type.carbon:[[@LINE+10]]:3: error: cannot implicitly convert expression of type `WrongSelf` to `Class` [ConversionFailure]
// CHECK:STDERR: ws.F();
// CHECK:STDERR: ^~
// CHECK:STDERR: fail_self_wrong_type.carbon:[[@LINE+7]]:3: note: type `WrongSelf` does not implement interface `Core.ImplicitAs(Class)` [MissingImplInMemberAccessInContext]
// CHECK:STDERR: ws.F();
// CHECK:STDERR: ^~
// CHECK:STDERR: fail_self_wrong_type.carbon:[[@LINE-10]]:8: note: initializing function parameter [InCallToFunctionParam]
// CHECK:STDERR: fn F(self: Class);
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
ws.F();
}
// --- fail_self_not_first.carbon
library "[[@TEST_NAME]]";
class Class {
// `self` must be the first explicit parameter.
// CHECK:STDERR: fail_self_not_first.carbon:[[@LINE+4]]:22: error: `self` must be the first explicit parameter [SelfNotFirstParam]
// CHECK:STDERR: fn F(other: Class, self: Self);
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR:
fn F(other: Class, self: Self);
}
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