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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/handle_binding_pattern.cpp
+67 -18
View File
@@ -13,6 +13,7 @@
#include "toolchain/check/inst.h"
#include "toolchain/check/interface.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/name_ref.h"
#include "toolchain/check/pattern.h"
#include "toolchain/check/period_self.h"
#include "toolchain/check/return.h"
@@ -57,12 +58,14 @@ static auto IsValidParamForIntroducer(Context& context, Parse::NodeId node_id,
bool is_generic) -> bool {
switch (introducer_kind) {
case Lex::TokenKind::Fn: {
// `self` in the implicit parameter list is diagnosed separately (see
// `SelfInImplicitParamList`), so skip it here to avoid a redundant
// diagnostic.
if (context.full_pattern_stack().CurrentKind() ==
FullPatternStack::Kind::ImplicitParamList &&
!(is_generic || name_id == SemIR::NameId::SelfValue)) {
CARBON_DIAGNOSTIC(
ImplictParamMustBeConstant, Error,
"implicit parameters of functions must be constant or `self`");
CARBON_DIAGNOSTIC(ImplictParamMustBeConstant, Error,
"implicit parameters of functions must be constant");
context.emitter().Emit(node_id, ImplictParamMustBeConstant);
return false;
}
@@ -112,8 +115,10 @@ namespace {
// expression may be interpreted as a type or a form, depending on the binding
// kind.
struct BindingPatternTypeInfo {
// The parse node representing the expression.
Parse::AnyExprId node_id;
// The parse node representing the expression. For a `self` binding with an
// omitted type this is the binding pattern node itself, since there is no
// separate type expression.
Parse::NodeId node_id;
// The inst representing the converted value of that expression. For a `:?`
// binding the expression is converted to type `Core.Form`; otherwise it is
// converted to type `type`.
@@ -124,10 +129,21 @@ struct BindingPatternTypeInfo {
};
} // namespace
// Handle the type position of a binding pattern.
// Handle the type position of a binding pattern. For a `self` binding with an
// omitted type, `self_type_inst_id` is the synthesized `Self` type expression
// and there is no type expression on the node stack to pop.
static auto HandleAnyBindingPatternType(Context& context,
Parse::NodeKind node_kind)
Parse::NodeId binding_node_id,
Parse::NodeKind node_kind,
SemIR::InstId self_type_inst_id)
-> BindingPatternTypeInfo {
if (self_type_inst_id.has_value()) {
auto as_type = ExprAsType(context, binding_node_id, self_type_inst_id);
return {.node_id = binding_node_id,
.inst_id = as_type.inst_id,
.type_component_id = as_type.type_id};
}
auto [node_id, original_inst_id] = context.node_stack().PopExprWithNodeId();
if (node_kind == Parse::FormBindingPattern::Kind) {
@@ -144,10 +160,12 @@ static auto HandleAnyBindingPatternType(Context& context,
}
// TODO: make this function shorter by factoring pieces out.
static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
Parse::NodeKind node_kind,
bool is_unused = false) -> bool {
auto type_expr = HandleAnyBindingPatternType(context, node_kind);
static auto HandleAnyBindingPattern(
Context& context, Parse::NodeId node_id, Parse::NodeKind node_kind,
bool is_unused = false,
SemIR::InstId self_type_inst_id = SemIR::InstId::None) -> bool {
auto type_expr = HandleAnyBindingPatternType(context, node_id, node_kind,
self_type_inst_id);
if (context.types()
.GetAsInst(type_expr.type_component_id)
.Is<SemIR::TypeComponentOf>()) {
@@ -228,13 +246,29 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
type_expr.type_component_id);
};
// A `self` binding can only appear in an implicit parameter list.
if (name_id == SemIR::NameId::SelfValue &&
!context.node_stack().PeekIs(Parse::NodeKind::ImplicitParamListStart)) {
CARBON_DIAGNOSTIC(
SelfOutsideImplicitParamList, Error,
"`self` can only be declared in an implicit parameter list");
context.emitter().Emit(node_id, SelfOutsideImplicitParamList);
// A `self` binding must be the first parameter in the explicit parameter
// list (see proposal #7016). Here we can reject `self` in the implicit
// parameter list or outside any parameter list; that it must be *first* in
// the explicit list is checked once the full list is known (see
// `BuildFunctionDecl`).
if (name_id == SemIR::NameId::SelfValue) {
switch (context.full_pattern_stack().CurrentKind()) {
case FullPatternStack::Kind::ExplicitParamList:
break;
case FullPatternStack::Kind::ImplicitParamList: {
CARBON_DIAGNOSTIC(
SelfInImplicitParamList, Error,
"`self` must be declared in the explicit parameter list");
context.emitter().Emit(node_id, SelfInImplicitParamList);
break;
}
default: {
CARBON_DIAGNOSTIC(SelfOutsideParamList, Error,
"`self` can only be declared in a parameter list");
context.emitter().Emit(node_id, SelfOutsideParamList);
break;
}
}
}
if (node_kind == Parse::NodeKind::CompileTimeBindingPattern &&
@@ -399,6 +433,21 @@ auto HandleParseNode(Context& context, Parse::LetBindingPatternId node_id)
Parse::NodeKind::LetBindingPattern);
}
auto HandleParseNode(Context& context, Parse::SelfBindingPatternId node_id)
-> bool {
// A `self` binding with an omitted type behaves like `self: Self`. There is
// no type expression in the parse tree, so synthesize a reference to `Self`
// into the current subpattern region and feed it in as the binding's type.
auto self_type =
LookupUnqualifiedName(context, node_id, SemIR::NameId::SelfType);
auto self_type_inst_id = BuildNameRef(
context, node_id, SemIR::NameId::SelfType,
self_type.scope_result.target_inst_id(), self_type.specific_id);
return HandleAnyBindingPattern(context, node_id,
Parse::NodeKind::LetBindingPattern,
/*is_unused=*/false, self_type_inst_id);
}
auto HandleParseNode(Context& context, Parse::VarBindingPatternId node_id)
-> bool {
return HandleAnyBindingPattern(context, node_id,