mirror of
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
115 lines
4.0 KiB
C++
115 lines
4.0 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/diagnostics/diagnostic.h"
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#include "toolchain/lex/token_kind.h"
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#include "toolchain/parse/context.h"
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#include "toolchain/parse/handle.h"
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#include "toolchain/parse/node_kind.h"
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namespace Carbon::Parse {
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auto HandleLet(Context& context) -> void {
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auto state = context.PopState();
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// These will start at the `let`.
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context.PushState(state, StateKind::LetFinishAsRegular);
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context.PushState(state, StateKind::LetAfterPatternAsRegular);
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context.PushStateForPattern(StateKind::Pattern, /*in_var_pattern=*/false,
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/*in_unused_pattern=*/false,
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PrecedenceGroup::ForTopLevelPattern());
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}
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auto HandleAssociatedConstant(Context& context) -> void {
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auto state = context.PopState();
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// Parse the associated constant pattern: identifier :! type
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auto identifier = context.ConsumeIf(Lex::TokenKind::Identifier);
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if (!identifier) {
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CARBON_DIAGNOSTIC(ExpectedAssociatedConstantIdentifier, Error,
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"expected identifier in associated constant declaration");
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context.emitter().Emit(*context.position(),
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ExpectedAssociatedConstantIdentifier);
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state.has_error = true;
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}
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auto colon_exclaim = context.ConsumeIf(Lex::TokenKind::ColonExclaim);
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if (identifier && !colon_exclaim) {
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CARBON_DIAGNOSTIC(ExpectedAssociatedConstantColonExclaim, Error,
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"found runtime binding pattern in associated constant "
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"declaration; expected a `:!` binding");
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context.emitter().Emit(*context.position(),
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ExpectedAssociatedConstantColonExclaim);
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state.has_error = true;
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}
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if (!identifier || !colon_exclaim) {
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auto end_token = context.SkipPastLikelyEnd(*(context.position() - 1));
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context.AddNode(NodeKind::AssociatedConstantDecl, end_token,
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/*has_error=*/true);
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state.has_error = true;
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return;
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}
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context.AddLeafNode(NodeKind::IdentifierNameNotBeforeSignature, *identifier);
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state.token = *colon_exclaim;
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context.PushState(state, StateKind::LetFinishAsAssociatedConstant);
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context.PushState(state, StateKind::LetAfterPatternAsAssociatedConstant);
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context.PushState(StateKind::Expr);
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}
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static auto HandleLetAfterPattern(Context& context, NodeKind init_kind)
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-> void {
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auto state = context.PopState();
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if (state.has_error) {
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if (auto after_pattern =
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context.FindNextOf({Lex::TokenKind::Equal, Lex::TokenKind::Semi})) {
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context.SkipTo(*after_pattern);
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}
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}
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if (auto equals = context.ConsumeIf(Lex::TokenKind::Equal)) {
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context.AddLeafNode(init_kind, *equals);
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context.PushState(StateKind::Expr);
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}
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}
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auto HandleLetAfterPatternAsRegular(Context& context) -> void {
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HandleLetAfterPattern(context, NodeKind::LetInitializer);
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}
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auto HandleLetAfterPatternAsAssociatedConstant(Context& context) -> void {
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auto state = context.PopState();
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context.AddNode(NodeKind::AssociatedConstantNameAndType, state.token,
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state.has_error);
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context.PushState(state);
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HandleLetAfterPattern(context, NodeKind::AssociatedConstantInitializer);
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}
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static auto HandleLetFinish(Context& context, NodeKind node_kind) -> void {
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auto state = context.PopState();
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auto end_token = state.token;
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if (context.PositionIs(Lex::TokenKind::Semi)) {
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end_token = context.Consume();
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} else {
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context.DiagnoseExpectedDeclSemi(Lex::TokenKind::Let);
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state.has_error = true;
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end_token = context.SkipPastLikelyEnd(state.token);
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}
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context.AddNode(node_kind, end_token, state.has_error);
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}
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auto HandleLetFinishAsRegular(Context& context) -> void {
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HandleLetFinish(context, NodeKind::LetDecl);
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}
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auto HandleLetFinishAsAssociatedConstant(Context& context) -> void {
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HandleLetFinish(context, NodeKind::AssociatedConstantDecl);
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}
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} // namespace Carbon::Parse
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