feat(intl): implement Intl.Locale (#5344)

[proggeramlug]

Summary

Implements Intl.Locale (issue #5344, the largest missing-constructor bucket in the intl402 tail), backed by icu_locale_core's data-free BCP-47 / UTS #35 parser. Previously new Intl.Locale(...) threw "undefined is not a constructor", which also blocked many other intl402 tests that construct a Locale during setup.

What's implemented

• Constructor — tag (string or Locale instance) + options, with ApplyOptionsToTag / ApplyUnicodeExtensionToTag resolution in spec-mandated order (language, script, region, variants, then ca/co/hc/kf/kn/nu). Validation: invalid subtags / out-of-range enums / empty or <3-char keyword type values → RangeError; non-string/non-object tag → TypeError.
• Getters (real prototype accessors, { get, enumerable:false, configurable:true }): baseName, language, script, region, variants, calendar, caseFirst, collation, hourCycle, numberingSystem, numeric.
• Methods: toString, maximize, minimize (the latter two are best-effort — likely-subtags need CLDR data, out of scope for the data-free parser).

Notable wiring

• ensure_function_prototype_object gains a Locale gate (mirroring the existing Temporal one) so new Intl.Locale() returns the populated prototype instead of shadowing it with a fresh empty one.
• The intl-locale feature now enables icu_locale_core/alloc explicitly (it was previously only pulled in transitively by temporal), so the auto-optimize build of a Temporal-free program that touches Intl.Locale links cleanly.
• Feature detection enables intl-locale on any Intl.Locale reference.

Results

scripts/test262_subset.py --dir intl402/Locale --all-features (node v26 oracle): 0 → 86/151 (57%).

Remaining failures are out of scope or known gaps:

• ~25 need CLDR data — the 2023 Locale-Info methods (getCalendars/getWeekInfo/getTimeZones/…) and alias / likely-subtags resolution (mo→ro, SU→AM, islamicc→islamic-civil, maximize/minimize). These need icu_locale + CLDR, not the data-free icu_locale_core.
• ~7 Symbol.toStringTag — pre-existing Perry limitation (Object.prototype.toString ignores inherited Symbol.toStringTag; affects the existing Intl formatters too).
• ~7 newTarget-detection / node-version artifacts, ~4 firstDayOfWeek (deferred), a few validation edges.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added Intl.Locale API support, including new Intl.Locale(...), toString, and maximize/minimize.
  • Implemented locale parsing and properties/options (language, script, region, variants, and Unicode extension values like calendar, collation, numbering system, numeric, etc.), with validation and RangeError for structurally invalid input.
• Bug Fixes
  • Improved handling of Intl.Locale constructor prototypes to preserve any pre-populated prototype object.
• Build/Tooling
  • Improved feature detection for Intl.Locale usage to recognize more Intl.*.Locale-related access patterns.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8332c77f-ba35-43b0-8367-f596569d7269

📥 Commits

Reviewing files that changed from the base of the PR and between fe4e134 and 422839a.

📒 Files selected for processing (5)

• crates/perry-runtime/Cargo.toml
• crates/perry-runtime/src/intl.rs
• crates/perry-runtime/src/intl/locale.rs
• crates/perry-runtime/src/object/class_registry.rs
• crates/perry/src/commands/compile/collect_modules/feature_detect.rs

🚧 Files skipped from review as they are similar to previous changes (3)

• crates/perry/src/commands/compile/collect_modules/feature_detect.rs
• crates/perry-runtime/Cargo.toml
• crates/perry-runtime/src/object/class_registry.rs

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📝 Walkthrough

Walkthrough

Adds Intl.Locale support behind the intl-locale feature flag. This includes a BCP-47/UTS#35 parsing and canonicalization pipeline using icu_locale_core, a full constructor with options application, property getters, prototype installation into the Intl namespace, a prototype registry guard matching the existing Temporal pattern, and a HIR-level feature detection trigger.

Changes

Intl.Locale implementation

Layer / File(s)	Summary
Feature configuration and module setup crates/perry-runtime/Cargo.toml, crates/perry-runtime/src/intl.rs	intl-locale feature gains icu_locale_core/alloc sub-feature; locale submodule introduced with feature-gated re-exports of install_locale_constructor and is_locale_ctor; install_intl_namespace updated to conditionally invoke the constructor installer.
Locale parsing and validation pipeline crates/perry-runtime/src/intl/locale.rs	Defines KEY_LOCALE_TAG and LOCALE_PROTO_BITS thread-local cell; implements BCP-47 tag parsing via icu_locale_core, unicode-extension keyword reading, option validation and subtag application (raising RangeError on invalid values), and canonical locale string construction via build_locale_string; includes is_locale_ctor identity check for constructor recognition.
Constructor thunk and instance methods crates/perry-runtime/src/intl/locale.rs	Constructor thunk allocates Intl.Locale instances with internal [[Kind]] and [[Locale]] fields and prototype linkage from LOCALE_PROTO_BITS; toString returns the stored canonical tag; maximize and minimize clone the stored tag into new Locale wrappers preserving the prototype chain.
Property getter implementations crates/perry-runtime/src/intl/locale.rs	All exported property getters (baseName, language, script, region, variants, calendar, caseFirst, collation, hourCycle, numberingSystem, numeric) re-parse the stored canonical locale string on demand and return the corresponding value or undefined; numeric includes boolean semantics based on -u-kn presence/value.
Prototype installation and namespace wiring crates/perry-runtime/src/intl/locale.rs	install_proto_getter allocates getter closures and installs them as non-settable configurable accessors on the prototype; install_locale_constructor creates the prototype, installs methods and accessor getters, sets Symbol.toStringTag to "Intl.Locale", caches prototype bits in LOCALE_PROTO_BITS, and registers the constructor on the Intl namespace object.
Prototype registry guard and feature detection crates/perry-runtime/src/object/class_registry.rs, crates/perry/src/commands/compile/collect_modules/feature_detect.rs	ensure_function_prototype_object is extended to preserve pre-populated .prototype for Intl.Locale constructors via is_locale_ctor, mirroring the Temporal guard. HIR feature detection gains a property: "Locale" match to set ctx.uses_intl_locale.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related issues

• PerryTS/perry#5344: Directly addresses the missing Intl.Locale constructor implementation with feature detection, which resolves the "Locale: 137" constructor failures reported in test262 intl402 test suite failures.

Possibly related PRs

• PerryTS/perry#5320: Both PRs are tied to the shared intl-locale ICU feature gate—main PR extends feature detection and runtime to add Intl.Locale, while the retrieved PR uses the same gate for locale-tag canonicalization powering Intl.getCanonicalLocales/supportedLocalesOf.
• PerryTS/perry#5359: Both PRs implement Intl.Locale by modifying crates/perry-runtime/src/intl.rs (wiring/installation and constructor/prototype setup), so changes are directly in the same codepath.

Poem

🐇 A hop through BCP-47 land,
Where locale tags meet a careful hand,
The bunny parsed each script and region,
With icu_locale_core as its legion.
RangeError for the ones gone wrong,
And Intl.Locale joins the throng! 🌍

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat(intl): implement Intl.Locale (#5344)' clearly and concisely summarizes the main feature being added—the implementation of the Intl.Locale constructor—which is the primary focus of all changes in the pull request.
Description check	✅ Passed	The description covers the main feature implementation, lists concrete changes across multiple files, explains notable wiring/infrastructure changes, provides test results, and includes the required checklist with all items marked. The description is comprehensive and well-structured.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch worktree-intl-locale-5344

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch worktree-intl-locale-5344

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[proggeramlug]

Superseded by #5359, which already implemented Intl.Locale for #5344 and merged to main (commit b0e9f48) while this was in progress. #5359's implementation is strictly more complete (it includes a likely-subtags table for maximize/minimize, which this PR deferred), so there's nothing here to add. Closing as a duplicate.