ucd: Rewrite parser to be faster & more flexible by joshuamegnauth54 · Pull Request #8611 · RustPython/RustPython

joshuamegnauth54 · 2026-08-30T02:08:18Z

Related: #8599

My original parser was monolithic and inflexible. It worked as intended for the derived data files, but anything more complicated required hacky code. For example, the original parser always expected to build a vector of values, yet sometimes we required other data structures such as BTreeMaps.

I split up the parser into helper functions that are both cleaner and more flexible. The actual parser should still yield the same results - this doesn't "fix" anything yet. However, this is preliminary work for fixing more of UCD since we will need a more flexible parser for fixes like the linked PR.

Closes #xxxx

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Summary

Rewrite compile time Unicode parser to be more flexible.

Summary by CodeRabbit

Refactor
- Improved the organization and generation of Unicode data.
- Unicode data is now separated by property, including character categories, numeric values, text direction, character width, and decomposition information.
- Updated handling supports both current Unicode data and Unicode 3.2 compatibility data.
- No user-facing behavior or public API changes are expected.

coderabbitai · 2026-08-30T02:08:25Z

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crates/unicode/build.rs

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📝 Walkthrough

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Changes

The Unicode build script now uses a shared line iterator and slice writers. Latest and Unicode 3.2 data are parsed once, then processed by per-property generators. Generated tables are split into individual includes in data.rs.

Unicode build generation

Layer / File(s)	Summary
Reader and output infrastructure `crates/unicode/build.rs`	`UnicodeLineReader` parses Unicode data lines. Shared writers emit generated slices. File helpers select input data and create output files.
Property-specific generation `crates/unicode/build.rs`	Latest and Unicode 3.2 parsers generate decomposition, membership, numeric, category, width, bidi, binary-property, combining-class, and numeric-type tables.
Parser orchestration and data wiring `crates/unicode/build.rs`, `crates/unicode/src/data.rs`	`drive_parsers` runs all parser functions in parallel. `data.rs` includes each generated table separately.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🔵 Low · up to a942b

This PR rewrites compile-time Unicode table generation and runs generators in parallel; if parsing or generation fails after output creation, partially written files may remain at their final paths and complicate subsequent builds or recovery. The change is otherwise confined to build-time generation and is mergeable with explicit owner awareness or follow-up to stage and atomically publish outputs.

Suggested reviewers: youknowone

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 31.03% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: rewriting the Unicode parser to improve speed and flexibility.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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codspeed · 2026-08-31T17:06:04Z

Merging this PR will not alter performance

✅ 36 untouched benchmarks

_{Comparing joshuamegnauth54:ucd-rewrite-parser (a942ba1) with main (6a3a8b0)}

coderabbitai

Actionable comments posted: 1

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Inline comments:
In `@crates/unicode/build.rs`:
- Around line 249-255: Update the decomposition table generation around
write_slice_flat, DECOMP_COMPAT, and DECOMP_RANGE to preserve append/code-point
order instead of sorting the formatted output. If ordering is required, sort
decomp_lines by code point before calculating decomp_ranges and offsets, then
emit both tables without further sorting so Ucd::decomposition binary search and
offset indexing remain aligned.

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crates/unicode/build.rs
crates/unicode/src/data.rs

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Related: RustPython#8599 My original parser was monolithic and inflexible. It worked as intended for the derived data files, but anything more complicated required hacky code. For example, the original parser always expected to build a vector of values, yet sometimes we required other data structures such as BTreeMaps. I split up the parser into helper functions that are both cleaner and more flexible. The actual parser should still yield the same results - this doesn't "fix" anything yet. However, this is preliminary work for fixing more of UCD since we will need a more flexible parser for fixes like the linked PR.

youknowone

👍

Related: #8599 My original parser was monolithic and inflexible. It worked as intended for the derived data files, but anything more complicated required hacky code. For example, the original parser always expected to build a vector of values, yet sometimes we required other data structures such as BTreeMaps. I split up the parser into helper functions that are both cleaner and more flexible. The actual parser should still yield the same results - this doesn't "fix" anything yet. However, this is preliminary work for fixing more of UCD since we will need a more flexible parser for fixes like the linked PR.

joshuamegnauth54 marked this pull request as ready for review August 31, 2026 16:55

joshuamegnauth54 force-pushed the ucd-rewrite-parser branch from e105e3d to 411e6bf Compare August 31, 2026 16:55

coderabbitai Bot reviewed Aug 31, 2026

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Comment thread crates/unicode/build.rs Outdated

joshuamegnauth54 force-pushed the ucd-rewrite-parser branch from 411e6bf to a942ba1 Compare August 31, 2026 17:17

youknowone approved these changes Aug 31, 2026

View reviewed changes

youknowone merged commit 5b5f4c3 into RustPython:main Aug 31, 2026
29 checks passed

joshuamegnauth54 deleted the ucd-rewrite-parser branch September 2, 2026 02:42

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ucd: Rewrite parser to be faster & more flexible - #8611

ucd: Rewrite parser to be faster & more flexible#8611
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joshuamegnauth54 commented Aug 30, 2026 •

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