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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
25 lines
1.1 KiB
Plaintext
25 lines
1.1 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/let/fail_empty.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/let/fail_empty.carbon
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// CHECK:STDERR: fail_empty.carbon:[[@LINE+4]]:4: error: expected pattern [ExpectedPattern]
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// CHECK:STDERR: let;
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// CHECK:STDERR: ^
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// CHECK:STDERR:
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let;
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// CHECK:STDOUT: - filename: fail_empty.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: 'LetIntroducer', text: 'let'},
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// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
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// CHECK:STDOUT: {kind: 'LetDecl', text: ';', subtree_size: 3},
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// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
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// CHECK:STDOUT: ]
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