mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-09-24 20:10:13 +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
49 lines
2.7 KiB
Plaintext
49 lines
2.7 KiB
Plaintext
// 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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//
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// AUTOUPDATE
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// TIP: To test this file alone, run:
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// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/match/fail_missing_case_pattern.carbon
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// TIP: To dump output, run:
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// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/match/fail_missing_case_pattern.carbon
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fn f() -> i32 {
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match (3) {
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// CHECK:STDERR: fail_missing_case_pattern.carbon:[[@LINE+4]]:10: error: expected pattern [ExpectedPattern]
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// CHECK:STDERR: case => { return 2; }
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// CHECK:STDERR: ^~
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// CHECK:STDERR:
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case => { return 2; }
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}
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return 0;
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}
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// CHECK:STDOUT: - filename: fail_missing_case_pattern.carbon
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// CHECK:STDOUT: parse_tree: [
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// CHECK:STDOUT: {kind: 'FileStart', text: ''},
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// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
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// CHECK:STDOUT: {kind: 'IdentifierNameMaybeBeforeSignature', text: 'f'},
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// CHECK:STDOUT: {kind: 'ExplicitParamListStart', text: '('},
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// CHECK:STDOUT: {kind: 'ExplicitParamList', text: ')', subtree_size: 2},
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// CHECK:STDOUT: {kind: 'IntTypeLiteral', text: 'i32'},
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// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 2},
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// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 7},
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// CHECK:STDOUT: {kind: 'MatchIntroducer', text: 'match'},
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// CHECK:STDOUT: {kind: 'MatchConditionStart', text: '('},
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// CHECK:STDOUT: {kind: 'IntLiteral', text: '3'},
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// CHECK:STDOUT: {kind: 'MatchCondition', text: ')', subtree_size: 3},
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// CHECK:STDOUT: {kind: 'MatchStatementStart', text: '{', subtree_size: 5},
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// CHECK:STDOUT: {kind: 'MatchCaseIntroducer', text: 'case'},
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// CHECK:STDOUT: {kind: 'InvalidParse', text: '=>', has_error: yes},
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// CHECK:STDOUT: {kind: 'MatchCase', text: '=>', has_error: yes, subtree_size: 3},
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// CHECK:STDOUT: {kind: 'MatchHandlerStart', text: '=>', has_error: yes, subtree_size: 4},
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// CHECK:STDOUT: {kind: 'MatchHandler', text: '=>', has_error: yes, subtree_size: 5},
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// CHECK:STDOUT: {kind: 'MatchStatement', text: '}', subtree_size: 11},
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// CHECK:STDOUT: {kind: 'ReturnStatementStart', text: 'return'},
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// CHECK:STDOUT: {kind: 'IntLiteral', text: '0'},
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// CHECK:STDOUT: {kind: 'ReturnStatement', text: ';', subtree_size: 3},
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// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 22},
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// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
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// CHECK:STDOUT: ]
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