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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/array/init_dependent_bound.carbon
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+11 -8
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@@ -56,6 +56,7 @@ fn G(template N:! i32) {
fn H() { G(3); }
// CHECK:STDOUT: --- generic_empty.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
@@ -96,11 +97,11 @@ fn H() { G(3); }
// CHECK:STDOUT: %pattern_type: type = pattern_type %array_type.loc7_29.2 [symbolic = %pattern_type (constants.%pattern_type.bd6)]
// CHECK:STDOUT: %array: @G.%array_type.loc7_29.2 (%array_type.1b3) = tuple_value () [symbolic = %array (constants.%array.ca4)]
// CHECK:STDOUT: %Destroy.lookup_impl_witness: <witness> = lookup_impl_witness %array_type.loc7_29.2, @Destroy [symbolic = %Destroy.lookup_impl_witness (constants.%Destroy.lookup_impl_witness)]
// CHECK:STDOUT: %Destroy.facet: %Destroy.type = facet_value %array_type.loc7_29.2, (%Destroy.lookup_impl_witness) [symbolic = %Destroy.facet (constants.%Destroy.facet.a52)]
// CHECK:STDOUT: %Destroy.WithSelf.Op.type: type = fn_type @Destroy.WithSelf.Op, @Destroy.WithSelf(%Destroy.facet) [symbolic = %Destroy.WithSelf.Op.type (constants.%Destroy.WithSelf.Op.type.a67)]
// CHECK:STDOUT: %.loc7_3.2: type = fn_type_with_self_type %Destroy.WithSelf.Op.type, %Destroy.facet [symbolic = %.loc7_3.2 (constants.%.1e5)]
// CHECK:STDOUT: %impl.elem0.loc7_3.2: @G.%.loc7_3.2 (%.1e5) = impl_witness_access %Destroy.lookup_impl_witness, element0 [symbolic = %impl.elem0.loc7_3.2 (constants.%impl.elem0)]
// CHECK:STDOUT: %specific_impl_fn.loc7_3.2: <specific function> = specific_impl_function %impl.elem0.loc7_3.2, @Destroy.WithSelf.Op(%Destroy.facet) [symbolic = %specific_impl_fn.loc7_3.2 (constants.%specific_impl_fn)]
// CHECK:STDOUT: %Destroy.facet.loc7_3.2: %Destroy.type = facet_value %array_type.loc7_29.2, (%Destroy.lookup_impl_witness) [symbolic = %Destroy.facet.loc7_3.2 (constants.%Destroy.facet.a52)]
// CHECK:STDOUT: %Destroy.WithSelf.Op.type: type = fn_type @Destroy.WithSelf.Op, @Destroy.WithSelf(%Destroy.facet.loc7_3.2) [symbolic = %Destroy.WithSelf.Op.type (constants.%Destroy.WithSelf.Op.type.a67)]
// CHECK:STDOUT: %.loc7_3.3: type = fn_type_with_self_type %Destroy.WithSelf.Op.type, %Destroy.facet.loc7_3.2 [symbolic = %.loc7_3.3 (constants.%.1e5)]
// CHECK:STDOUT: %impl.elem0.loc7_3.2: @G.%.loc7_3.3 (%.1e5) = impl_witness_access %Destroy.lookup_impl_witness, element0 [symbolic = %impl.elem0.loc7_3.2 (constants.%impl.elem0)]
// CHECK:STDOUT: %specific_impl_fn.loc7_3.2: <specific function> = specific_impl_function %impl.elem0.loc7_3.2, @Destroy.WithSelf.Op(%Destroy.facet.loc7_3.2) [symbolic = %specific_impl_fn.loc7_3.2 (constants.%specific_impl_fn)]
// CHECK:STDOUT:
// CHECK:STDOUT: fn() {
// CHECK:STDOUT: !entry:
@@ -119,8 +120,10 @@ fn H() { G(3); }
// CHECK:STDOUT: %array_type.loc7_29.1: type = array_type %int_0, %T.ref [symbolic = %array_type.loc7_29.2 (constants.%array_type.1b3)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %arr: ref @G.%array_type.loc7_29.2 (%array_type.1b3) = ref_binding arr, %arr.var
// CHECK:STDOUT: %impl.elem0.loc7_3.1: @G.%.loc7_3.2 (%.1e5) = impl_witness_access constants.%Destroy.lookup_impl_witness, element0 [symbolic = %impl.elem0.loc7_3.2 (constants.%impl.elem0)]
// CHECK:STDOUT: %impl.elem0.loc7_3.1: @G.%.loc7_3.3 (%.1e5) = impl_witness_access constants.%Destroy.lookup_impl_witness, element0 [symbolic = %impl.elem0.loc7_3.2 (constants.%impl.elem0)]
// CHECK:STDOUT: %bound_method.loc7_3.1: <bound method> = bound_method %arr.var, %impl.elem0.loc7_3.1
// CHECK:STDOUT: %Destroy.facet.loc7_3.1: %Destroy.type = facet_value constants.%array_type.1b3, (constants.%Destroy.lookup_impl_witness) [symbolic = %Destroy.facet.loc7_3.2 (constants.%Destroy.facet.a52)]
// CHECK:STDOUT: %.loc7_3.2: %Destroy.type = converted constants.%array_type.1b3, %Destroy.facet.loc7_3.1 [symbolic = %Destroy.facet.loc7_3.2 (constants.%Destroy.facet.a52)]
// CHECK:STDOUT: %specific_impl_fn.loc7_3.1: <specific function> = specific_impl_function %impl.elem0.loc7_3.1, @Destroy.WithSelf.Op(constants.%Destroy.facet.a52) [symbolic = %specific_impl_fn.loc7_3.2 (constants.%specific_impl_fn)]
// CHECK:STDOUT: %bound_method.loc7_3.2: <bound method> = bound_method %arr.var, %specific_impl_fn.loc7_3.1
// CHECK:STDOUT: %Destroy.WithSelf.Op.call: init %empty_tuple.type = call %bound_method.loc7_3.2(%arr.var)
@@ -143,9 +146,9 @@ fn H() { G(3); }
// CHECK:STDOUT: %pattern_type => constants.%pattern_type.6be
// CHECK:STDOUT: %array => constants.%array.497
// CHECK:STDOUT: %Destroy.lookup_impl_witness => constants.%custom_witness.df9
// CHECK:STDOUT: %Destroy.facet => constants.%Destroy.facet.396
// CHECK:STDOUT: %Destroy.facet.loc7_3.2 => constants.%Destroy.facet.396
// CHECK:STDOUT: %Destroy.WithSelf.Op.type => constants.%Destroy.WithSelf.Op.type.ccc
// CHECK:STDOUT: %.loc7_3.2 => constants.%.a02
// CHECK:STDOUT: %.loc7_3.3 => constants.%.a02
// CHECK:STDOUT: %impl.elem0.loc7_3.2 => constants.%Destroy.Op
// CHECK:STDOUT: %specific_impl_fn.loc7_3.2 => constants.%Destroy.Op
// CHECK:STDOUT: }