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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
87 lines
3.4 KiB
C++
87 lines
3.4 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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auto HandlePattern(Context& context) -> void {
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auto state = context.PopState();
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switch (context.PositionKind()) {
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case Lex::TokenKind::OpenParen:
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context.PushStateForPattern(StateKind::PatternListAsTuple,
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state.in_var_pattern, state.in_unused_pattern,
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state.binding_context,
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state.ambient_precedence);
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break;
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case Lex::TokenKind::Var:
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context.PushStateForPattern(StateKind::VariablePattern,
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state.in_var_pattern, state.in_unused_pattern,
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state.binding_context,
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state.ambient_precedence);
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break;
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case Lex::TokenKind::Unused:
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context.PushStateForPattern(StateKind::UnusedPattern,
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state.in_var_pattern, state.in_unused_pattern,
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state.binding_context,
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state.ambient_precedence);
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break;
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case Lex::TokenKind::Template:
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case Lex::TokenKind::Generic:
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case Lex::TokenKind::Runtime:
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case Lex::TokenKind::Ref:
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// `self` is always a binding, even when its type is omitted (and so is not
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// followed by a `:`).
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case Lex::TokenKind::SelfValueIdentifier:
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context.PushStateForPattern(StateKind::BindingPattern,
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state.in_var_pattern, state.in_unused_pattern,
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state.binding_context,
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state.ambient_precedence);
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break;
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default:
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if (context.PositionKind().is_word() &&
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context.PositionKind(Lookahead::NextToken)
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.is_binding_pattern_operator()) {
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context.PushStateForPattern(
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StateKind::BindingPattern, state.in_var_pattern,
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state.in_unused_pattern, state.binding_context,
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state.ambient_precedence);
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break;
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}
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context.PushState(StateKind::ExprPattern);
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context.PushStateForExpr(state.ambient_precedence);
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break;
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}
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}
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auto HandleExprPattern(Context& context) -> void {
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auto state = context.PopState();
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// If we parsed an expression followed by a binding operator, we most likely
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// have a malformed attempt to introduce a binding pattern that we interpreted
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// as an expression pattern, so diagnose that here rather than diagnosing a
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// missing `;` at an outer level.
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if (context.PositionKind().is_binding_pattern_operator()) {
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if (!state.has_error) {
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CARBON_DIAGNOSTIC(ExpectedBindingName, Error,
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"unexpected expression before {0} in binding pattern",
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Lex::TokenKind);
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// TODO: Underline the parsed expression.
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context.emitter().Emit(*context.position(), ExpectedBindingName,
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context.PositionKind());
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state.has_error = true;
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}
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context.Consume();
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// It'd be nice to skip the type expression here too, but we can't determine
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// the end of it.
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}
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if (state.has_error) {
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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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