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https://github.com/carbon-language/carbon-lang.git
synced 2026-09-24 22:02:23 +01:00
Richard Smith
181a592b8c
When parsing a pattern, if we encounter something that isn't pattern syntax, try parsing as an expression instead. We only need one-token lookahead to distinguish pattern syntax from expression syntax. Track a precedence group through pattern parsing so that we can allow different kinds of expressions in a top-level pattern (such as the operand of `let`) and in a nested pattern (such as a subpattern of a tuple pattern or within grouping parens). For example, we do not allow `case if ...`, and for now I've chosen to also not allow logical or relational operators at the top level of a pattern, so `case 1 + 1` is OK, but `case 1 == 1` and `case true and false` require parentheses. This decision should be ratified or revisited by a design proposal. Very basic check support is also provided, only sufficient to form an `ExprPattern` instruction and nothing beyond that. For now, all pattern matching against an `ExprPattern` fails with a TODO error. To support that, I've switched from calling `BeginSubpattern` in the parent handler of a pattern and `EndSubpatternAs*` in the pattern handler itself to calling both functions in parent handlers, with `EndSubpattern` converting an expression into an expression pattern where needed. Depends on #6976. Assisted-by: Gemini via Google Antigravity
38 lines
1.3 KiB
C++
38 lines
1.3 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 HandleUnusedPattern(Context& context) -> void {
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auto state = context.PopState();
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if (state.in_unused_pattern) {
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CARBON_DIAGNOSTIC(NestedUnused, Error,
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"`unused` nested within another `unused`");
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context.emitter().Emit(*context.position(), NestedUnused);
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state.has_error = true;
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}
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context.PushState(StateKind::FinishUnusedPattern);
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context.ConsumeChecked(Lex::TokenKind::Unused);
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context.PushStateForPattern(StateKind::Pattern, state.in_var_pattern,
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/*in_unused_pattern=*/true,
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state.ambient_precedence);
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}
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auto HandleFinishUnusedPattern(Context& context) -> void {
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auto state = context.PopState();
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context.AddNode(NodeKind::UnusedPattern, state.token, state.has_error);
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// Propagate errors to the parent state so that they can take different
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// actions on invalid patterns.
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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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