Fix grammar for block comments#2191
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| `/**/` | ||
| | `/***/` | ||
| | `/*` | ||
| ^ | ||
| ( ~[`*` `!`] | `**` | BLOCK_COMMENT_OR_DOC ) | ||
| ( BLOCK_COMMENT_OR_DOC | ~`*/` )* | ||
| ^ ( BLOCK_COMMENT_OR_DOC | ~`*/` )* |
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With the changes, the first two branches aren't needed, right?
Separately, we might as well avoid using ~ here on this multiple character lookahead.
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Indeed, it is no longer needed, I have removed it and the use of ~.
This fixes an issue with the block comment grammar with nested block comments. For example, this would fail to match `/*/* test */*/` because of the following: The open slash of the inner block comment matches `~[`*` `!`]` which then misinterprets the rest of the inner block comment as being normal characters, and prevents the nesting from working correctly. The original intent with this formulation was to prevent it from matching an inner or outer block doc comment. This is no longer needed because we are now defining the order with the COMMENT production, and the doc comments come before block comments. This also changes the order of BLOCK_COMMENT_OR_DOC, but that is not strictly necessary because once inside a block comment, everything is comment text. rustc does not expose nested comments as being distinct. I mainly ordered them to be consistent with COMMENT (and in case I forgot anything). The implementation for this is at [`Cursor::block_comment`](https://github.com/rust-lang/rust/blob/859951e3c7c9d0322c39bad49221937455bdffcd/compiler/rustc_lexer/src/lib.rs#L782-L817).
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In the grammar rule for `BLOCK_COMMENT`, we indent the rule expression for the content of the block comment. We had put the cut ahead of this rule, but the resulting indentation makes it seem as though the cut is scoped to this subpart when it in fact applies to all remaining parts of the rule. The potential confusion here is particularly subtle because the rule for the content of a block comment is followed by a Kleene star -- if the cut only applied to this subpart, it would be superfluous. Let's move the cut to after the opening `/*` to avoid this.
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Looks good; thanks. |
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Update books ## rust-embedded/book 4 commits in 99d0341ff4e06757490af8fceee790c4ede50bc0..e88aa4403b4bf2071c8df9509160477e40179099 2026-02-28 20:13:44 UTC to 2026-02-28 20:07:25 UTC - Clarify that a mini usb cable is used on the STM32F3DISCOVERY (rust-embedded/book#381) - Update outdated qemu documentation (rust-embedded/book#403) - Add TRACE32 to Debuggers section (rust-embedded/book#406) - Add a link to Rust for Zephyr (rust-embedded/book#407) ## rust-lang/nomicon 4 commits in b8f254a991b8b7e8f704527f0d4f343a4697dfa9..cc6a6bae8c3bfa389974e533c54694662c1a9de6 2026-02-27 23:27:18 UTC to 2026-02-26 22:57:03 UTC - Fix `Vec::push_all` ptr code in exception-safety (rust-lang/nomicon#418) - Clarify parameter and argument compatibility (rust-lang/nomicon#516) - Improve grammar in Variance section (rust-lang/nomicon#515) - Explicit `extern "C"` ABI for FFI (rust-lang/nomicon#520) ## rust-lang/reference 7 commits in 50a1075e879be75aeec436252c84eef0fad489f4..c49e89cc8c7c2c43ca625a8d5b7ad9a53a9ce978 2026-03-04 15:39:00 UTC to 2026-03-01 06:34:18 UTC - Resolve grammar rules in link reference definitions (rust-lang/reference#2198) - Support non-ASCII Unicode in grammar rule names (rust-lang/reference#2196) - Fix grammar for block comments (rust-lang/reference#2191) - Fix an EN grammar error & add an item to place expr context list (rust-lang/reference#2189) - Align attribute template with applied conventions (rust-lang/reference#2194) - Update shebang (rust-lang/reference#2192) - Remove RESERVED_NUMBER (rust-lang/reference#2193)
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Update books ## rust-embedded/book 4 commits in 99d0341ff4e06757490af8fceee790c4ede50bc0..e88aa4403b4bf2071c8df9509160477e40179099 2026-02-28 20:13:44 UTC to 2026-02-28 20:07:25 UTC - Clarify that a mini usb cable is used on the STM32F3DISCOVERY (rust-embedded/book#381) - Update outdated qemu documentation (rust-embedded/book#403) - Add TRACE32 to Debuggers section (rust-embedded/book#406) - Add a link to Rust for Zephyr (rust-embedded/book#407) ## rust-lang/nomicon 4 commits in b8f254a991b8b7e8f704527f0d4f343a4697dfa9..cc6a6bae8c3bfa389974e533c54694662c1a9de6 2026-02-27 23:27:18 UTC to 2026-02-26 22:57:03 UTC - Fix `Vec::push_all` ptr code in exception-safety (rust-lang/nomicon#418) - Clarify parameter and argument compatibility (rust-lang/nomicon#516) - Improve grammar in Variance section (rust-lang/nomicon#515) - Explicit `extern "C"` ABI for FFI (rust-lang/nomicon#520) ## rust-lang/reference 7 commits in 50a1075e879be75aeec436252c84eef0fad489f4..c49e89cc8c7c2c43ca625a8d5b7ad9a53a9ce978 2026-03-04 15:39:00 UTC to 2026-03-01 06:34:18 UTC - Resolve grammar rules in link reference definitions (rust-lang/reference#2198) - Support non-ASCII Unicode in grammar rule names (rust-lang/reference#2196) - Fix grammar for block comments (rust-lang/reference#2191) - Fix an EN grammar error & add an item to place expr context list (rust-lang/reference#2189) - Align attribute template with applied conventions (rust-lang/reference#2194) - Update shebang (rust-lang/reference#2192) - Remove RESERVED_NUMBER (rust-lang/reference#2193)
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Update books ## rust-embedded/book 4 commits in 99d0341ff4e06757490af8fceee790c4ede50bc0..e88aa4403b4bf2071c8df9509160477e40179099 2026-02-28 20:13:44 UTC to 2026-02-28 20:07:25 UTC - Clarify that a mini usb cable is used on the STM32F3DISCOVERY (rust-embedded/book#381) - Update outdated qemu documentation (rust-embedded/book#403) - Add TRACE32 to Debuggers section (rust-embedded/book#406) - Add a link to Rust for Zephyr (rust-embedded/book#407) ## rust-lang/nomicon 4 commits in b8f254a991b8b7e8f704527f0d4f343a4697dfa9..cc6a6bae8c3bfa389974e533c54694662c1a9de6 2026-02-27 23:27:18 UTC to 2026-02-26 22:57:03 UTC - Fix `Vec::push_all` ptr code in exception-safety (rust-lang/nomicon#418) - Clarify parameter and argument compatibility (rust-lang/nomicon#516) - Improve grammar in Variance section (rust-lang/nomicon#515) - Explicit `extern "C"` ABI for FFI (rust-lang/nomicon#520) ## rust-lang/reference 7 commits in 50a1075e879be75aeec436252c84eef0fad489f4..c49e89cc8c7c2c43ca625a8d5b7ad9a53a9ce978 2026-03-04 15:39:00 UTC to 2026-03-01 06:34:18 UTC - Resolve grammar rules in link reference definitions (rust-lang/reference#2198) - Support non-ASCII Unicode in grammar rule names (rust-lang/reference#2196) - Fix grammar for block comments (rust-lang/reference#2191) - Fix an EN grammar error & add an item to place expr context list (rust-lang/reference#2189) - Align attribute template with applied conventions (rust-lang/reference#2194) - Update shebang (rust-lang/reference#2192) - Remove RESERVED_NUMBER (rust-lang/reference#2193)
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Rollup merge of #153619 - rustbot:docs-update, r=ehuss Update books ## rust-embedded/book 4 commits in 99d0341ff4e06757490af8fceee790c4ede50bc0..e88aa4403b4bf2071c8df9509160477e40179099 2026-02-28 20:13:44 UTC to 2026-02-28 20:07:25 UTC - Clarify that a mini usb cable is used on the STM32F3DISCOVERY (rust-embedded/book#381) - Update outdated qemu documentation (rust-embedded/book#403) - Add TRACE32 to Debuggers section (rust-embedded/book#406) - Add a link to Rust for Zephyr (rust-embedded/book#407) ## rust-lang/nomicon 4 commits in b8f254a991b8b7e8f704527f0d4f343a4697dfa9..cc6a6bae8c3bfa389974e533c54694662c1a9de6 2026-02-27 23:27:18 UTC to 2026-02-26 22:57:03 UTC - Fix `Vec::push_all` ptr code in exception-safety (rust-lang/nomicon#418) - Clarify parameter and argument compatibility (rust-lang/nomicon#516) - Improve grammar in Variance section (rust-lang/nomicon#515) - Explicit `extern "C"` ABI for FFI (rust-lang/nomicon#520) ## rust-lang/reference 7 commits in 50a1075e879be75aeec436252c84eef0fad489f4..c49e89cc8c7c2c43ca625a8d5b7ad9a53a9ce978 2026-03-04 15:39:00 UTC to 2026-03-01 06:34:18 UTC - Resolve grammar rules in link reference definitions (rust-lang/reference#2198) - Support non-ASCII Unicode in grammar rule names (rust-lang/reference#2196) - Fix grammar for block comments (rust-lang/reference#2191) - Fix an EN grammar error & add an item to place expr context list (rust-lang/reference#2189) - Align attribute template with applied conventions (rust-lang/reference#2194) - Update shebang (rust-lang/reference#2192) - Remove RESERVED_NUMBER (rust-lang/reference#2193)
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This fixes an issue with the block comment grammar with nested block comments. For example, this would fail to match
/*/* test */*/because of the following:The open slash of the inner block comment matches
~[*]which then misinterprets the rest of the inner block comment as being normal characters, and prevents the nesting from working correctly.The original intent with this formulation was to prevent it from matching an inner or outer block doc comment. This is no longer needed because we are now defining the order with the COMMENT production, and the doc comments come before block comments.
This also changes the order of BLOCK_COMMENT_OR_DOC, but that is not strictly necessary because once inside a block comment, everything is comment text. rustc does not expose nested comments as being distinct. I mainly ordered them to be consistent with COMMENT (and in case I forgot anything).
The implementation for this is at
Cursor::block_comment.