Support int range patterns by cknitt · Pull Request #8894 · rescript-lang/rescript

cknitt · 2026-10-18T09:55:23Z

Third step of #7028, stacked on #8893.

switch now accepts int range patterns, and their bounds may mix ints and chars, since char is an alias of int (#8892). They use the Tpat_interval node from #8893, so a range costs the same however wide it is.

let status = code =>
  switch code {
  | 200 .. 299 => "success"
  | 301 | 302 | 307 | 308 => "redirect"
  | 400 .. 499 => "client error"
  | 500 .. 599 => "server error"
  | _ => "unknown"
  }

function status(code) {
  if (code >= 309) {
    if (code >= 500) {
      if (code >= 600) {
        return "unknown";
      } else {
        return "server error";
      }
    } else if (code >= 400) {
      return "client error";
    } else {
      return "unknown";
    }
  }
  if (code < 200) {
    return "unknown";
  }
  if (code < 300) {
    return "success";
  }
  switch (code) {
    case 300 :
    case 303 :
    case 304 :
    case 305 :
    case 306 :
      return "unknown";
    case 301 :
    case 302 :
    case 307 :
    case 308 :
      return "redirect";
  }
}

Type checker: accepts int and mixed bounds; reversed bounds are swapped, as for chars. Ranges of other constants (1.0 .. 5.0) still report Invalid_interval, whose message now reads "Only int and char intervals are supported in patterns."
Exhaustiveness: int switches are never exhaustive, as before. The missing-case example is the least uncovered value from 0 up, else the greatest one below 0, or _ if all of int32 is covered.

New tests:

int_range_test.res: negative, hex, reversed and mixed bounds, large ranges, HTTP status codes, ranges in several columns.
super_errors: a missing-case example below 0 (warning 8), and Invalid_interval with float bounds. That fixture replaces pattern_interval_non_char.res, since 1 .. 5 is now valid.

A differential fuzzer ran 600 switches over int, char and mixed ranges (negative bounds, or-patterns, guards, tuples, options). For every input, the results equal a reference evaluation. Three programs hit the pre-existing Matching.comp_exit crash described in #8893.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo

pkg-pr-new · 2026-10-18T10:15:05Z

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commit: 24a773a

cknitt · 2026-10-18T11:06:12Z

@codex review

chatgpt-codex-connector · 2026-10-18T11:06:28Z

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-18T11:51:56.819617Z	`4d2e390`	Manual request

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Reviewed commit: 9a4e37f913

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A missing-case example in a char column took the kind of the first pattern, so a value that no char literal can denote was printed as an invalid one: a switch covering every char literal suggested `'\u{110000}'`. Such values are now printed as ints. Example (rescript): let f = c => switch c { | '\u{0}' .. '\u{10FFFF}' => 1 } Before (text): You forgot to handle a possible case here, for example: | '\u{110000}' After (text): You forgot to handle a possible case here, for example: | 1114112 Source: tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res, compiled with the parent commit and with this one. Review: Codex found this for mixed ranges on #8894, where an example below 0 was printed as a char; the cause is here. Area: typechecker tests Output: unchanged Errors: ERROR_VARIANTS.md warnings section lists warning_8_char_range_beyond.res Tests: +tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo Signed-off-by: Christoph Knittel <ck@cca.io>

codecov · 2026-10-18T11:24:22Z

Codecov Report

❌ Patch coverage is 88.46154% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.04%. Comparing base (02d5ac2) to head (24a773a).

Files with missing lines	Patch %	Lines
compiler/ml/typecore.ml	83.33%	2 Missing ⚠️
compiler/ml/parmatch.ml	92.85%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           char-intervals    #8894   +/-   ##
===============================================
  Coverage           81.04%   81.04%           
===============================================
  Files                 455      455           
  Lines               63660    63675   +15     
===============================================
+ Hits                51591    51605   +14     
- Misses              12069    12070    +1

Files with missing lines	Coverage Δ
compiler/ml/parmatch.ml	`77.26% <92.85%> (+0.17%)`	⬆️
compiler/ml/typecore.ml	`86.59% <83.33%> (-0.01%)`	⬇️

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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cknitt · 2026-10-18T11:49:35Z

@codex review

chatgpt-codex-connector · 2026-10-18T11:51:55Z

Codex Review: Didn't find any major issues. Hooray!

Reviewed commit: 4d2e390417

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cristianoc

Legit

A missing-case example in a char column took the kind of the first pattern, so a value that no char literal can denote was printed as an invalid one: a switch covering every char literal suggested `'\u{110000}'`. Such values are now printed as ints. Example (rescript): let f = c => switch c { | '\u{0}' .. '\u{10FFFF}' => 1 } Before (text): You forgot to handle a possible case here, for example: | '\u{110000}' After (text): You forgot to handle a possible case here, for example: | 1114112 Source: tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res, compiled with the parent commit and with this one. Review: Codex found this for mixed ranges on #8894, where an example below 0 was printed as a char; the cause is here. Area: typechecker tests Output: unchanged Errors: ERROR_VARIANTS.md warnings section lists warning_8_char_range_beyond.res Tests: +tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo Signed-off-by: Christoph Knittel <ck@cca.io>

`switch` now accepts int ranges such as `200 .. 299`, and bounds that mix ints and chars, since `char` is an alias of `int`. They use the `Tpat_interval` node char ranges compile to, so a range costs the same however wide it is. Ranges of other constants, such as `1.0 .. 5.0`, still report `Invalid_interval`, whose message now names int and char intervals. Int switches are never exhaustive, as before: a missing-case example is the least uncovered value from 0 up, else the greatest one below 0. Example (rescript): let status = code => switch code { | 200 .. 299 => "success" | 301 | 302 | 307 | 308 => "redirect" | 400 .. 499 => "client error" | 500 .. 599 => "server error" | _ => "unknown" } After (js): function status(code) { if (code >= 309) { if (code >= 500) { if (code >= 600) { return "unknown"; } else { return "server error"; } } else if (code >= 400) { return "client error"; } else { return "unknown"; } } if (code < 200) { return "unknown"; } if (code < 300) { return "success"; } switch (code) { case 300 : case 303 : case 304 : case 305 : case 306 : return "unknown"; case 301 : case 302 : case 307 : case 308 : return "redirect"; } } Source: tests/tests/src/int_range_test.mjs in the diff. Before this commit the example reported "Only character intervals are supported in patterns." Review: Does a switch covering all ints count as exhaustive? No. Ints are never matched exhaustively, so warning 8 still reports `_` for a switch on `-0x80000000 .. -1 | 0 .. 0x7FFFFFFF`, as it does for constants. Review: Can a mixed range give an invalid example? Codex found that a range from a char to an int covering all non-negative ints suggested a char for -1. Examples are written as chars only when they are valid code points, a fix in the parent commit; warning_8_mixed_range_example.res covers this case. Review: How was it checked? A fuzzer generated 600 switches over int, char and mixed ranges with negative bounds, or-patterns, guards, tuples and options; the results equal a reference evaluation for every input. Three programs hit `Fatal error: Matching.comp_exit`; each reduces to `| _ => ... | p1 | p2 if g() => ...`, which crashes the parent commits the same way with char patterns. Area: typechecker tests Output: unchanged, existing programs compile the same; int ranges are new Formatting: unchanged Formats: none PPX: unchanged Editor: unchanged Tests: +tests/tests/src/int_range_test.res +tests/build_tests/super_errors/fixtures/warning_8_int_range_example.res +tests/build_tests/super_errors/fixtures/warning_8_mixed_range_example.res +tests/build_tests/super_errors/fixtures/pattern_interval_float.res -tests/build_tests/super_errors/fixtures/pattern_interval_non_char.res Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo Signed-off-by: Christoph Knittel <ck@cca.io>

github-actions · 2026-10-19T06:38:59Z

Semantic diff: https://cdn.rescript-lang.org/semantic-diff/pr-8894/index.html?v=24a773a08

* Represent char range patterns with a typed-tree node A char range pattern such as `'a' .. 'z'` used to be expanded by the type checker into an or-pattern with one constant per character, so compile time and memory grew with the width of the range. It is now one `Tpat_interval` node. Exhaustiveness and match compilation split each column at the bounds of its ranges into pieces that every range covers fully or not at all, so the work depends on the number of patterns, not on the number of characters. Missing-case warnings show ranges instead of listing every character. Example (rescript): let f = (a, b) => switch (a, b) { | ('a' .. 'z', 'a' .. 'z') => 1 | (_, '\u{0}' .. '`') => 2 } Before (text): You forgot to handle a possible case here, for example: | ('t', '{') | ('u', '{') | ('v', '{') | ('w', '{') | ('x', '{') | ('y', '{') | ('z', '{') After (text): You forgot to handle a possible case here, for example: | ('a' .. 'z', '{') | ('\x00', 'a') Source: tests/build_tests/super_errors/fixtures/warning_8_char_range_example.res, compiled with the parent commit and with this one. Review: Is the generated JavaScript the same? Every committed snapshot is byte-identical. A differential fuzzer (900 random switches over overlapping char ranges, or-patterns, guards, tuples and options) compiled each program with the parent commit and with this one: results equal a reference evaluation for every input, warning numbers and locations are equal, and the JS differs in shape for some programs and is 0.4% smaller in total (296,645 -> 295,495 characters). Review: Why are intervals precompiled like or-patterns? An expanded range used to be an or-pattern, whose row is compiled once in a handler. Doing the same for an interval whose row tests further columns keeps that sharing; dividing such rows by piece instead made the fuzzer's output 16% larger. Review: Why is the action of a range stored as shared? The switch emits it for each value of the range. An expanded range shared it the same way, because its values had equal actions; a copy per value would declare the action's variables twice in one JavaScript scope. Review: Are int ranges such as `1 .. 5` accepted? Not yet; they still report `Invalid_interval`. The node and the algorithms already work on int and char constants, for a follow-up. Area: typechecker lambda analysis tests Output: unchanged, all committed generated JS is byte-identical (char_range_test.mjs changes with its source) Formatting: unchanged Formats: cmt (Caml1999T045 -> Caml1999T046) PPX: unchanged, Ppat_interval already exists in the v0 parsetree Editor: unchanged; analysis visits the new node like a constant Tests: ~tests/tests/src/char_range_test.res +tests/build_tests/super_errors/fixtures/warning_8_char_range_example.res +tests/build_tests/super_errors/fixtures/warning_11_char_range_covered.res Measured: switch on '\u{0}' .. '\u{10FFFF}': 15.75 s and 1.78 GB -> 0.02 s and 19 MB (bsc wall time and max RSS, /usr/bin/time, parent commit vs this one); switch on '\u{0}' .. '\u{FFFF}': 0.55 s and 135 MB -> 0.02 s and 20 MB Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo Signed-off-by: Christoph Knittel <ck@cca.io> * Write missing-case examples beyond char literals as ints A missing-case example in a char column took the kind of the first pattern, so a value that no char literal can denote was printed as an invalid one: a switch covering every char literal suggested `'\u{110000}'`. Such values are now printed as ints. Example (rescript): let f = c => switch c { | '\u{0}' .. '\u{10FFFF}' => 1 } Before (text): You forgot to handle a possible case here, for example: | '\u{110000}' After (text): You forgot to handle a possible case here, for example: | 1114112 Source: tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res, compiled with the parent commit and with this one. Review: Codex found this for mixed ranges on #8894, where an example below 0 was printed as a char; the cause is here. Area: typechecker tests Output: unchanged Tests: +tests/build_tests/super_errors/fixtures/warning_8_char_range_beyond.res Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JALXUyHhkDqzcB3WuW9Svo Signed-off-by: Christoph Knittel <ck@cca.io> --------- Signed-off-by: Christoph Knittel <ck@cca.io> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

cknitt added this pull request to stack #8895 October 18, 2026 09:55

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cknitt requested a review from cristianoc October 18, 2026 12:05

cknitt marked this pull request as ready for review October 18, 2026 12:05

cknitt mentioned this pull request Oct 18, 2026

Remove the hashing fast paths from pattern matching #8900

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cristianoc approved these changes Oct 18, 2026

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This was referenced Oct 18, 2026

Make char an alias of int #8892

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Fix watch tests that flake on duplicate change events #8902

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cknitt force-pushed the char-int-ranges branch from 003b92e to 24a773a Compare October 19, 2026 06:38

cknitt merged commit 407c384 into master Oct 19, 2026
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cknitt deleted the char-int-ranges branch October 19, 2026 07:15

cknitt mentioned this pull request Oct 19, 2026

RFC: Revise char primitive #7028

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Support int range patterns - #8894

Support int range patterns#8894
cknitt merged 1 commit into
char-intervalsfrom
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