Add locale-sensitive casing

[mosuem]

Fixes #229
Fixes #336

• Works for ECMA
• Works for ICU4X - needs the right feature flags in the library build @robertbastian icu_casemap

Needs to land the artifact changes separately before landing this PR.

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
intl4x	Non-Breaking	0.10.1	0.10.2-wip	0.10.2	✔️

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

Coverage ⚠️

File	Coverage
pkgs/intl4x/hook/build.dart	💔 Not covered
pkgs/intl4x/lib/case_mapping.dart	💚 50 %
pkgs/intl4x/lib/intl4x.dart	💚 65 %
pkgs/intl4x/lib/src/case_mapping/case_mapping.dart	💚 83 %
pkgs/intl4x/lib/src/case_mapping/case_mapping_4x.dart	💚 50 %
pkgs/intl4x/lib/src/case_mapping/case_mapping_ecma.dart	💚 100 %
pkgs/intl4x/lib/src/case_mapping/case_mapping_impl.dart	💚 100 %
pkgs/intl4x/lib/src/case_mapping/case_mapping_stub.dart	💔 0 % ⬇️ NaN %
pkgs/intl4x/lib/src/case_mapping/case_mapping_stub_4x.dart	💔 0 % ⬇️ NaN %

This check for test coverage is informational (issues shown here will not fail the PR).

This check can be disabled by tagging the PR with skip-coverage-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Package publish validation ✔️

Package	Version	Status
package:intl	0.20.0-wip	WIP (no publish necessary)
package:intl4x	0.10.2-wip	WIP (no publish necessary)
package:intl_translation	0.20.1-wip	WIP (no publish necessary)
package:messages	0.2.0	already published at pub.dev
package:messages_builder	0.2.1	already published at pub.dev
package:messages_serializer	0.2.1	already published at pub.dev
package:messages_shrinker	0.2.2-wip	WIP (no publish necessary)

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[gnprice]

Excellent, looking forward to having this!

[robertbastian]

That's too many dots on the lowercase i. Does this pass?

[gnprice]

That's the same result as I get from the corresponding browser API:

> "İstanbul".toLocaleLowerCase('en-US')
'i̇stanbul'
> "İstanbul".toLocaleLowerCase('en-US')[1]
'̇'

The result changes with a Turkish locale, to be what I think you're expecting:

> "İstanbul".toLocaleLowerCase('tr-TR')
'istanbul'
> "İstanbul".toLocaleLowerCase('tr-TR')[1]
's'

This test should probably exercise the Turkish locale too:

Suggested change

	expect('İstanbul'.toLocaleLowerCase(enUS), 'i̇stanbul');
	expect('İstanbul'.toLocaleLowerCase(enUS), 'i̇stanbul');
	expect('İstanbul'.toLocaleLowerCase(trTR), 'istanbul');

so that the contrast is explicit. (It already does something very similar below on lines 16–17, but it's not obvious to the reader what that means for this "İstanbul" case.)

[robertbastian]

ah that makes sense

[gnprice]

That's the same result as I get from the corresponding browser API:

> "İstanbul".toLocaleLowerCase('en-US')
'i̇stanbul'
> "İstanbul".toLocaleLowerCase('en-US')[1]
'̇'

The result changes with a Turkish locale, to be what I think you're expecting:

> "İstanbul".toLocaleLowerCase('tr-TR')
'istanbul'
> "İstanbul".toLocaleLowerCase('tr-TR')[1]
's'

This test should probably exercise the Turkish locale too:

Suggested change

	expect('İstanbul'.toLocaleLowerCase(enUS), 'i̇stanbul');
	expect('İstanbul'.toLocaleLowerCase(enUS), 'i̇stanbul');
	expect('İstanbul'.toLocaleLowerCase(trTR), 'istanbul');

so that the contrast is explicit. (It already does something very similar below on lines 16–17, but it's not obvious to the reader what that means for this "İstanbul" case.)

[gnprice]

ISTR there's one other case besides Turkish where locale-specific case-mapping is interesting — I think it was Lithuanian. It'd be nice to have a test case demonstrating that too.

[gnprice]

nit: I like the Locale.parse way of expressing the locales that you use below — those strings like en-US are nice and compact, and are familiar from how locales are identified in other systems. Consider using it throughout the test:

Suggested change

	expect('\u0130'.toLocaleLowerCase(const Locale(language: 'tr')), 'i');
	expect('\u0130'.toLocaleLowerCase(enUS), isNot('i'));
	expect('\u0130'.toLocaleLowerCase(Locale.parse('tr'), 'i');
	expect('\u0130'.toLocaleLowerCase(Locale.parse('en-US'), isNot('i'));