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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/class/method/generic_method.carbon
Vendored
+23 -22
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@@ -14,10 +14,11 @@
class Class(T:! type) {
var a: T;
fn F[self: Self](n: T);
fn F(self, n: T);
}
fn Class(T:! type).F[unused self: Self](unused n: T) {}
fn Class(T:! type).F(unused self, unused n: T) {}
// CHECK:STDOUT: --- generic_method.carbon
// CHECK:STDOUT:
@@ -63,10 +64,10 @@ fn Class(T:! type).F[unused self: Self](unused n: T) {}
// CHECK:STDOUT: %T.loc15_14.2: type = symbolic_binding T, 0 [symbolic = %T.loc15_14.1 (constants.%T)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %Class.F.decl: %Class.F.type = fn_decl @Class.F [symbolic = constants.%Class.F] {
// CHECK:STDOUT: %self.param_patt: @Class.F.%pattern_type.loc17_12 (%pattern_type.36e) = value_param_pattern [concrete]
// CHECK:STDOUT: %self.patt: @Class.F.%pattern_type.loc17_12 (%pattern_type.36e) = at_binding_pattern self, %self.param_patt [concrete]
// CHECK:STDOUT: %n.param_patt: @Class.F.%pattern_type.loc17_21 (%pattern_type.51d) = value_param_pattern [concrete]
// CHECK:STDOUT: %n.patt: @Class.F.%pattern_type.loc17_21 (%pattern_type.51d) = at_binding_pattern n, %n.param_patt [concrete]
// CHECK:STDOUT: %self.param_patt: @Class.F.%pattern_type.loc17_8 (%pattern_type.36e) = value_param_pattern [concrete]
// CHECK:STDOUT: %self.patt: @Class.F.%pattern_type.loc17_8 (%pattern_type.36e) = at_binding_pattern self, %self.param_patt [concrete]
// CHECK:STDOUT: %n.param_patt: @Class.F.%pattern_type.loc17_15 (%pattern_type.51d) = value_param_pattern [concrete]
// CHECK:STDOUT: %n.patt: @Class.F.%pattern_type.loc17_15 (%pattern_type.51d) = at_binding_pattern n, %n.param_patt [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc20_14.1: type = splice_block %.loc20_14.2 [concrete = type] {
// CHECK:STDOUT: %.Self: %type = symbolic_binding .Self [symbolic_self = constants.%.Self]
@@ -74,9 +75,9 @@ fn Class(T:! type).F[unused self: Self](unused n: T) {}
// CHECK:STDOUT: }
// CHECK:STDOUT: %T.loc20: type = symbolic_binding T, 0 [symbolic = @Class.%T.loc15_14.1 (constants.%T)]
// CHECK:STDOUT: %self.param.loc20: @Class.F.%Class (%Class) = value_param call_param0
// CHECK:STDOUT: %.loc20_35.1: type = splice_block %Self.ref.loc20 [symbolic = %Class (constants.%Class)] {
// CHECK:STDOUT: %.loc20_35.2: type = specific_constant constants.%Class, @Class(constants.%T) [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %Self.ref.loc20: type = name_ref Self, %.loc20_35.2 [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %.loc20_29.1: type = splice_block %Self.ref.loc20 [symbolic = %Class (constants.%Class)] {
// CHECK:STDOUT: %.loc20_29.2: type = specific_constant constants.%Class, @Class(constants.%T) [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %Self.ref.loc20: type = name_ref Self, %.loc20_29.2 [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %self.loc20: @Class.F.%Class (%Class) = value_binding self, %self.param.loc20
// CHECK:STDOUT: %n.param.loc20: @Class.F.%T.loc17 (%T) = value_param call_param1
@@ -100,15 +101,15 @@ fn Class(T:! type).F[unused self: Self](unused n: T) {}
// CHECK:STDOUT: class {
// CHECK:STDOUT: %.loc16: @Class.%Class.elem (%Class.elem) = field_decl a, element0 [concrete]
// CHECK:STDOUT: %Class.F.decl: @Class.%Class.F.type (%Class.F.type) = fn_decl @Class.F [symbolic = @Class.%Class.F (constants.%Class.F)] {
// CHECK:STDOUT: %self.param_patt: @Class.F.%pattern_type.loc17_12 (%pattern_type.36e) = value_param_pattern [concrete]
// CHECK:STDOUT: %self.patt: @Class.F.%pattern_type.loc17_12 (%pattern_type.36e) = at_binding_pattern self, %self.param_patt [concrete]
// CHECK:STDOUT: %n.param_patt: @Class.F.%pattern_type.loc17_21 (%pattern_type.51d) = value_param_pattern [concrete]
// CHECK:STDOUT: %n.patt: @Class.F.%pattern_type.loc17_21 (%pattern_type.51d) = at_binding_pattern n, %n.param_patt [concrete]
// CHECK:STDOUT: %self.param_patt: @Class.F.%pattern_type.loc17_8 (%pattern_type.36e) = value_param_pattern [concrete]
// CHECK:STDOUT: %self.patt: @Class.F.%pattern_type.loc17_8 (%pattern_type.36e) = at_binding_pattern self, %self.param_patt [concrete]
// CHECK:STDOUT: %n.param_patt: @Class.F.%pattern_type.loc17_15 (%pattern_type.51d) = value_param_pattern [concrete]
// CHECK:STDOUT: %n.patt: @Class.F.%pattern_type.loc17_15 (%pattern_type.51d) = at_binding_pattern n, %n.param_patt [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %self.param.loc17: @Class.F.%Class (%Class) = value_param call_param0
// CHECK:STDOUT: %.loc17_14.1: type = splice_block %Self.ref.loc17 [symbolic = %Class (constants.%Class)] {
// CHECK:STDOUT: %.loc17_14.2: type = specific_constant constants.%Class, @Class(constants.%T) [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %Self.ref.loc17: type = name_ref Self, %.loc17_14.2 [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %.loc17_8.1: type = splice_block %Self.ref.loc17 [symbolic = %Class (constants.%Class)] {
// CHECK:STDOUT: %.loc17_8.2: type = specific_constant constants.%Class, @Class(constants.%T) [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %Self.ref.loc17: type = name_ref Self, %.loc17_8.2 [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %self.loc17: @Class.F.%Class (%Class) = value_binding self, %self.param.loc17
// CHECK:STDOUT: %n.param.loc17: @Class.F.%T.loc17 (%T) = value_param call_param1
@@ -129,12 +130,12 @@ fn Class(T:! type).F[unused self: Self](unused n: T) {}
// CHECK:STDOUT: generic fn @Class.F(@Class.%T.loc15_14.2: type) {
// CHECK:STDOUT: %T.loc17: type = symbolic_binding T, 0 [symbolic = %T.loc17 (constants.%T)]
// CHECK:STDOUT: %Class: type = class_type @Class, @Class(%T.loc17) [symbolic = %Class (constants.%Class)]
// CHECK:STDOUT: %pattern_type.loc17_12: type = pattern_type %Class [symbolic = %pattern_type.loc17_12 (constants.%pattern_type.36e)]
// CHECK:STDOUT: %pattern_type.loc17_21: type = pattern_type %T.loc17 [symbolic = %pattern_type.loc17_21 (constants.%pattern_type.51d)]
// CHECK:STDOUT: %pattern_type.loc17_8: type = pattern_type %Class [symbolic = %pattern_type.loc17_8 (constants.%pattern_type.36e)]
// CHECK:STDOUT: %pattern_type.loc17_15: type = pattern_type %T.loc17 [symbolic = %pattern_type.loc17_15 (constants.%pattern_type.51d)]
// CHECK:STDOUT:
// CHECK:STDOUT: !definition:
// CHECK:STDOUT: %require_complete.loc20_33: <witness> = require_complete_type %Class [symbolic = %require_complete.loc20_33 (constants.%require_complete.4d9)]
// CHECK:STDOUT: %require_complete.loc20_49: <witness> = require_complete_type %T.loc17 [symbolic = %require_complete.loc20_49 (constants.%require_complete.944)]
// CHECK:STDOUT: %require_complete.loc20_29: <witness> = require_complete_type %Class [symbolic = %require_complete.loc20_29 (constants.%require_complete.4d9)]
// CHECK:STDOUT: %require_complete.loc20_43: <witness> = require_complete_type %T.loc17 [symbolic = %require_complete.loc20_43 (constants.%require_complete.944)]
// CHECK:STDOUT:
// CHECK:STDOUT: fn(%self.param.loc20: @Class.F.%Class (%Class), %n.param.loc20: @Class.F.%T.loc17 (%T)) {
// CHECK:STDOUT: !entry:
@@ -158,7 +159,7 @@ fn Class(T:! type).F[unused self: Self](unused n: T) {}
// CHECK:STDOUT: specific @Class.F(constants.%T) {
// CHECK:STDOUT: %T.loc17 => constants.%T
// CHECK:STDOUT: %Class => constants.%Class
// CHECK:STDOUT: %pattern_type.loc17_12 => constants.%pattern_type.36e
// CHECK:STDOUT: %pattern_type.loc17_21 => constants.%pattern_type.51d
// CHECK:STDOUT: %pattern_type.loc17_8 => constants.%pattern_type.36e
// CHECK:STDOUT: %pattern_type.loc17_15 => constants.%pattern_type.51d
// CHECK:STDOUT: }
// CHECK:STDOUT: