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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
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toolchain/check/testdata/pointer/arrow.carbon
Vendored
+1 -1
View File
@@ -13,7 +13,7 @@
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/pointer/arrow.carbon
class C {
fn Member[self: Self]();
fn Member(self);
var field: C*;
}
toolchain/check/testdata/pointer/nested_const.carbon
Vendored
+3
View File
@@ -17,6 +17,7 @@ fn F(p: const (const (const i32*)*)) -> const i32 {
return **p;
}
// CHECK:STDOUT: --- nested_const.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
@@ -106,6 +107,8 @@ fn F(p: const (const (const i32*)*)) -> const i32 {
// CHECK:STDOUT: %.loc17_10.2: %const.6a8 = acquire_value %.loc17_10.1
// CHECK:STDOUT: %impl.elem0: %.367 = impl_witness_access constants.%Copy.impl_witness.0b0, element0 [concrete = constants.%const.as.Copy.impl.Op.9cf]
// CHECK:STDOUT: %bound_method.loc17_10.1: <bound method> = bound_method %.loc17_10.2, %impl.elem0
// CHECK:STDOUT: %Copy.facet: %Copy.type = facet_value constants.%i32, (constants.%Copy.impl_witness.0e0) [concrete = constants.%Copy.facet.987]
// CHECK:STDOUT: %.loc17_10.3: %Copy.type = converted constants.%i32, %Copy.facet [concrete = constants.%Copy.facet.987]
// CHECK:STDOUT: %specific_fn: <specific function> = specific_function %impl.elem0, @const.as.Copy.impl.Op(constants.%Copy.facet.987) [concrete = constants.%const.as.Copy.impl.Op.specific_fn]
// CHECK:STDOUT: %bound_method.loc17_10.2: <bound method> = bound_method %.loc17_10.2, %specific_fn
// CHECK:STDOUT: %const.as.Copy.impl.Op.call: init %const.6a8 = call %bound_method.loc17_10.2(%.loc17_10.2)