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Move self to the explicit () parameter list (proposal #7016) (#7272)

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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>
This commit is contained in:
Chandler Carruth
2026-06-10 15:30:43 +00:00
committed by GitHub
co-authored by josh11b
parent fb05da761f
commit 7871237c15
296 changed files with 6101 additions and 4899 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/testdata/interop/cpp/class/export/base.carbon
Vendored
+5 -5
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@@ -134,16 +134,16 @@ import Cpp;
// CHECK:STDERR:
abstract class Abstract {
// CHECK:STDERR: fail_todo_abstract_nonvirtual_dtor_but_virtual_fns.carbon:[[@LINE+10]]:3: error: initialization of abstract type `Abstract` [AbstractTypeInInit]
// CHECK:STDERR: abstract fn F[self: Self]();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: abstract fn F(self);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_abstract_nonvirtual_dtor_but_virtual_fns.carbon:[[@LINE-4]]:1: note: class was declared abstract here [ClassAbstractHere]
// CHECK:STDERR: abstract class Abstract {
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_abstract_nonvirtual_dtor_but_virtual_fns.carbon:[[@LINE+4]]:17: note: initializing function parameter [InCallToFunctionParam]
// CHECK:STDERR: abstract fn F[self: Self]();
// CHECK:STDERR: ^~~~~~~~~~
// CHECK:STDERR: abstract fn F(self);
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
abstract fn F[self: Self]();
abstract fn F(self);
}
inline Cpp '''
toolchain/check/testdata/interop/cpp/class/export/method.carbon
Vendored
+7 -7
View File
@@ -29,7 +29,7 @@ library "[[@TEST_NAME]]";
import Cpp;
class C {
fn M[self: Self]();
fn M(self);
}
inline Cpp '''
@@ -44,7 +44,7 @@ library "[[@TEST_NAME]]";
import Cpp;
class C {
fn M[self: Self]();
fn M(self);
}
inline Cpp '''
@@ -58,7 +58,7 @@ library "[[@TEST_NAME]]";
import Cpp;
class C {
fn M[ref self: Self]();
fn M(ref self);
}
inline Cpp '''
@@ -73,7 +73,7 @@ library "[[@TEST_NAME]]";
import Cpp;
class C {
fn M[ref self: Self]();
fn M(ref self);
}
inline Cpp '''
@@ -81,9 +81,9 @@ void F() {
// CHECK:STDERR: fail_ref_method_rvalue.carbon:[[@LINE+7]]:3: error: 'this' argument to member function 'M' is an rvalue, but function has non-const lvalue ref-qualifier [CppInteropParseError]
// CHECK:STDERR: 17 | Carbon::C().M();
// CHECK:STDERR: | ^
// CHECK:STDERR: fail_ref_method_rvalue.carbon:[[@LINE-8]]:25: note: 'M' declared here [CppInteropParseNote]
// CHECK:STDERR: 5 | fn M[ref self: Self]();
// CHECK:STDERR: | ^
// CHECK:STDERR: fail_ref_method_rvalue.carbon:[[@LINE-8]]:17: note: 'M' declared here [CppInteropParseNote]
// CHECK:STDERR: 5 | fn M(ref self);
// CHECK:STDERR: | ^
// CHECK:STDERR:
Carbon::C().M();
}
toolchain/check/testdata/interop/cpp/class/import/abstract.carbon
Vendored
+4 -4
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@@ -46,7 +46,7 @@ import Cpp library "abstract.h";
class C {
extend base: Cpp.A;
override fn f[unused ref self: Self]() {}
override fn f(unused ref self) {}
}
// --- fail_impl_mismatch_member.carbon
@@ -58,10 +58,10 @@ import Cpp library "abstract.h";
class C {
extend base: Cpp.A;
// CHECK:STDERR: fail_impl_mismatch_member.carbon:[[@LINE+4]]:3: error: override without compatible virtual in base class [OverrideWithoutVirtualInBase]
// CHECK:STDERR: override fn invalid[unused ref self: Self]() {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: override fn invalid(unused ref self) {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
override fn invalid[unused ref self: Self]() {}
override fn invalid(unused ref self) {}
}
// --- abstract_final.h
toolchain/check/testdata/interop/cpp/class/import/access.carbon
Vendored
+5 -5
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@@ -127,7 +127,7 @@ import Cpp library "non_function_member_protected.h";
class Derived {
extend base: Cpp.C;
fn F[self: Self]() {
fn F(self) {
//@dump-sem-ir-begin
let unused instance_data: i32 = self.instance_data;
let unused unqualified_static_data: i32 = static_data;
@@ -182,7 +182,7 @@ import Cpp library "non_function_member_private.h";
class Derived {
extend base: Cpp.C;
fn F[self: Self]() {
fn F(self) {
// CHECK:STDERR: fail_import_non_function_member_private_extend.carbon:[[@LINE+8]]:37: error: cannot access private member `instance_data` of type `Cpp.C` [ClassInvalidMemberAccess]
// CHECK:STDERR: let unused instance_data: i32 = self.instance_data;
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
@@ -313,7 +313,7 @@ import Cpp library "function_member_protected.h";
class Derived {
extend base: Cpp.C;
fn F[self: Self]() {
fn F(self) {
//@dump-sem-ir-begin
// TODO: It should be possible to call protected methods in the base class.
// CHECK:STDERR: fail_todo_import_function_member_protected_extend_call_instance_in_member.carbon:[[@LINE+8]]:22: error: no matching function for call to 'instance_fn' [CppInteropParseError]
@@ -337,7 +337,7 @@ import Cpp library "function_member_protected.h";
class Derived {
extend base: Cpp.C;
fn F[unused self: Self]() {
fn F(unused self) {
//@dump-sem-ir-begin
static_fn();
Derived.static_fn();
@@ -366,7 +366,7 @@ import Cpp library "function_member_private.h";
class Derived {
extend base: Cpp.C;
fn F[self: Self]() {
fn F(self) {
// CHECK:STDERR: fail_import_function_member_private.carbon:[[@LINE+7]]:5: error: cannot access private member `instance_fn` of type `Cpp.C` [ClassInvalidMemberAccess]
// CHECK:STDERR: self.instance_fn();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
toolchain/check/testdata/interop/cpp/class/import/dynamic.carbon
Vendored
+1 -1
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@@ -39,7 +39,7 @@ auto Use(Base& b) -> int {
base class Derived {
extend base: Cpp.Base;
virtual fn other_func[unused self: Self]() -> i32 {
virtual fn other_func(unused self) -> i32 {
return 3;
}
}