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https://github.com/carbon-language/carbon-lang.git
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Chandler Carruth
8be274cf60
Implement the toolchain side of proposal #7254, removing the `:!` binding syntax for generic and template parameters in favor of the keywords `generic`, `template`, and `runtime` plus contextual defaults for phase. For valid programs this is semantics-preserving: each binding resolves to the same phase, and produces the same SemIR, as it did under `:!`/`:`. The parser derives a binding's phase from its syntactic context plus any explicit phase keyword; new diagnostics and error recovery for misused keywords are described below. Implementation details for each component: - Lexer: remove the `:!` (`ColonExclaim`) token, move its virtual parse-node budget onto `:`, and add the `generic` and `runtime` keywords. - Parser: thread a `BindingContext` (`ExplicitParam`, `DeducedParam`, or `CompileTimeEntityParam`) from declaration introducers down through parameter lists to each binding pattern, using a one-token lookahead to distinguish a name-qualifier parameter list from a declaration's own final list. Parameters of a compile-time entity (`class`, `interface`, `constraint`, `choice`, `alias`, `export`, `namespace`) and deduced `[]` parameters default to checked generic; explicit function parameters and local bindings default to runtime. `HandleBindingPattern` resolves the phase from that context plus the keyword: a `generic` keyword needs no node of its own (the phase is carried by the binding's node kind), while a `runtime` keyword is preserved as a `RuntimeBindingName` node so `check` can name it in a diagnostic. A phase keyword that is merely redundant with the contextual default is diagnosed here, without invalidating the parse tree. - Check: a phase keyword that is invalid for its context (for example `runtime` on a checked-generic parameter) is diagnosed here, and recovers by building an error binding that still introduces the name so that later uses of it do not produce cascading errors. The removed `:!` syntax is now rejected as an ordinary parse error. The `form`/`:?`/`->?` ("extended types") portion of proposal #7254 is left for a separate change. Assisted-by: Claude Code
79 lines
2.7 KiB
C++
79 lines
2.7 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#include "toolchain/parse/context.h"
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#include "toolchain/parse/handle.h"
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namespace Carbon::Parse {
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static auto ExpectAsOrTypeExpression(Context& context) -> void {
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if (context.PositionIs(Lex::TokenKind::As)) {
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// as <expression> ...
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context.AddLeafNode(NodeKind::ImplDefaultSelfAs, context.Consume());
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context.PushState(StateKind::Expr);
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} else {
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// <expression> as <expression>...
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context.PushState(StateKind::ImplBeforeAs);
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context.PushStateForExpr(PrecedenceGroup::ForImplAs());
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}
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}
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auto HandleImplAfterIntroducer(Context& context) -> void {
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auto state = context.PopState();
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state.kind = StateKind::DeclOrDefinitionAsImpl;
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context.PushState(state);
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if (context.PositionIs(Lex::TokenKind::Forall)) {
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// forall [<implicit parameter list>] ...
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context.PushState(StateKind::ImplAfterForall);
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context.AddLeafNode(NodeKind::Forall, context.Consume());
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if (context.PositionIs(Lex::TokenKind::OpenSquareBracket)) {
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context.PushState(StateKind::PatternListAsImplicit, *context.position(),
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BindingContext::DeducedParam);
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} else {
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CARBON_DIAGNOSTIC(ImplExpectedAfterForall, Error,
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"expected `[` after `forall` in `impl` declaration");
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context.emitter().Emit(*context.position(), ImplExpectedAfterForall);
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context.ReturnErrorOnState();
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// If we aren't producing a node from the PatternListAsImplicit state,
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// we still need to create a node to be the child of the `ImplForall`
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// token created in the `ImplAfterForall` state.
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context.AddInvalidParse(*context.position());
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}
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} else {
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// One of:
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// as <expression> ...
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// <expression> as <expression>...
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ExpectAsOrTypeExpression(context);
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}
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}
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auto HandleImplAfterForall(Context& context) -> void {
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auto state = context.PopState();
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if (state.has_error) {
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context.ReturnErrorOnState();
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}
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// One of:
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// as <expression> ...
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// <expression> as <expression>...
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ExpectAsOrTypeExpression(context);
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}
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auto HandleImplBeforeAs(Context& context) -> void {
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auto state = context.PopState();
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if (auto as = context.ConsumeIf(Lex::TokenKind::As)) {
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context.AddNode(NodeKind::ImplTypeAs, *as, state.has_error);
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context.PushState(StateKind::Expr);
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} else {
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if (!state.has_error) {
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CARBON_DIAGNOSTIC(ImplExpectedAs, Error,
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"expected `as` in `impl` declaration");
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context.emitter().Emit(*context.position(), ImplExpectedAs);
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}
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context.ReturnErrorOnState();
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}
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}
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} // namespace Carbon::Parse
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