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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/lower/testdata/function/generic/call_basic.carbon
Vendored
+4 -4
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@@ -12,7 +12,7 @@
class C {
impl as Core.Copy {
fn Op[unused self: Self]() -> Self { return {}; }
fn Op(unused self) -> Self { return {}; }
}
}
@@ -60,12 +60,12 @@ fn M() {
// CHECK:STDOUT:
// CHECK:STDOUT: %type = type {}
// CHECK:STDOUT:
// CHECK:STDOUT: @C.val.loc15_51 = internal constant {} zeroinitializer
// CHECK:STDOUT: @C.val.loc15_43 = internal constant {} zeroinitializer
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @"_COp.C.Main:Copy.Core"(ptr sret({}) %return, ptr %self) #0 !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 1 %return, ptr align 1 @C.val.loc15_51, i64 0, i1 false), !dbg !10
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 1 %return, ptr align 1 @C.val.loc15_43, i64 0, i1 false), !dbg !10
// CHECK:STDOUT: ret void, !dbg !10
// CHECK:STDOUT: }
// CHECK:STDOUT:
@@ -284,7 +284,7 @@ fn M() {
// CHECK:STDOUT: !7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
// CHECK:STDOUT: !8 = !{!9}
// CHECK:STDOUT: !9 = !DILocalVariable(arg: 1, scope: !4, type: !7)
// CHECK:STDOUT: !10 = !DILocation(line: 15, column: 42, scope: !4)
// CHECK:STDOUT: !10 = !DILocation(line: 15, column: 34, scope: !4)
// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "Op", linkageName: "_COp.807eb4f2d3ed7e54:core.Destroy.Core", scope: null, file: !3, line: 43, type: !12, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !14)
// CHECK:STDOUT: !12 = !DISubroutineType(types: !13)
// CHECK:STDOUT: !13 = !{null, !7}