refactor: labeled expressions implementation

[timofei-iatsenko]

This is my attempt on fixing #241 and #239

This is more systematic refactoring rather ad-hoc fix. The refactoring make closer Rust implementation to a babel's one, so they not diverge.

Previously indexes for expression were allocated during processing a Message Phase in a message builder, in babel version those indexes where assigned during AST scanning phase, so it produced a diffrent result described in #241

Additionally ph macro was not processed uniformly. It was processed in some places but were skipped in other, for example:

<Plural value={ph({count: getCount()})} / > 

With this refactoring, ph support is added everywhere and processed uniformly.

Other changes:

1. I extracted all tests related to labeled expressions feature into separate file. It's easier to see all cases and work on the feature this way
2. I changed internal structures,

• TransformCtx (formerly MacroCtx) — global per-file context holding macro imports, options, directives, and runtime identifiers.
• MacroCtx<'a> — short-lived, created fresh for each macro invocation. Borrows &'a mut TransformCtx and owns its own expression index counter starting at 0.
• Free tokenization functions: tokenize_tpl, tokenize_expr_to_arg, try_tokenize_call_expr_as_choice_cmp, try_tokenize_expr, and get_choice_cases_from_obj are now free functions taking &mut MacroCtx explicitly, making the data flow clear.

[codecov]

Codecov Report

❌ Patch coverage is 90.88235% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.83%. Comparing base (32416e4) to head (43cfc14).

Files with missing lines	Patch %	Lines
crates/lingui_macro/src/macro_utils.rs	90.56%	20 Missing ⚠️
crates/lingui_macro/src/jsx_visitor.rs	84.05%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #244      +/-   ##
==========================================
- Coverage   95.06%   94.83%   -0.24%     
==========================================
  Files           9        9              
  Lines        2251     2325      +74     
==========================================
+ Hits         2140     2205      +65     
- Misses        111      120       +9     

Flag	Coverage Δ
unittests	94.83% <90.88%> (-0.24%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crates/lingui_macro/src/ast_utils.rs	90.80% <ø> (-0.41%)	⬇️
crates/lingui_macro/src/builder.rs	99.15% <100.00%> (+0.17%)	⬆️
crates/lingui_macro/src/js_macro_folder.rs	98.42% <100.00%> (+0.06%)	⬆️
crates/lingui_macro/src/lib.rs	91.09% <100.00%> (+0.01%)	⬆️
crates/lingui_macro/src/jsx_visitor.rs	86.95% <84.05%> (-1.49%)	⬇️
crates/lingui_macro/src/macro_utils.rs	91.72% <90.56%> (+2.50%)	⬆️

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[Copilot]

Pull request overview

Refactors the SWC Lingui macro tokenization/indexing to more closely mirror the Babel implementation, with a focus on consistent numeric placeholder allocation (source-order for ICU value, and not counting named placeholders) and uniform ph(...) handling across tokenization paths.

Changes:

• Replaced expression/ICU-choice tokens with a unified MsgArg model (name + value + optional ICU format/cases) and updated the builder accordingly.
• Introduced a split context model (TransformCtx per file + MacroCtx per macro invocation) and moved tokenization into free functions that operate on &mut MacroCtx.
• Reorganized/expanded tests and snapshots for labeled expressions and added coverage for ICU value index allocation order.

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/lingui_macro/src/tokens.rs	Refactors message tokens to use MsgArg for expressions/ICU arguments.
crates/lingui_macro/src/macro_utils.rs	Introduces TransformCtx/MacroCtx split and new tokenization helpers; adds ph(...) unwrapping and labeled-expression handling.
crates/lingui_macro/src/lib.rs	Updates transform entrypoints to use the new per-invocation MacroCtx and custom JSX visitor traversal.
crates/lingui_macro/src/jsx_visitor.rs	Reworks JSX traversal/tokenization to produce MsgArg tokens and handle ICU macros in source order.
crates/lingui_macro/src/js_macro_folder.rs	Adapts JS macro folding to new tokenization APIs and context types.
crates/lingui_macro/src/builder.rs	Updates message construction to consume MsgArg tokens (including ICU format/cases) and simplify value handling.
crates/lingui_macro/src/ast_utils.rs	Removes TS as expansion helper (moved/handled elsewhere).
crates/lingui_macro/tests/labeled_expressions.rs	New consolidated test file for labeled-expressions and ph scenarios (including error cases).
crates/lingui_macro/tests/jsx.rs	Removes labeled-expression test cases moved into labeled_expressions.rs.
crates/lingui_macro/tests/jsx_icu.rs	Adds regression tests for ICU value index allocation ordering.
crates/lingui_macro/tests/js_t.rs	Removes labeled-expression test cases moved into labeled_expressions.rs.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_ph_with_non_object_arg.snap	New snapshot covering invalid ph(variable) usage in JSX.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_ph_labels.snap	Updates snapshot source location and removes multi-prop case (now an error test).
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_ph_labeled_expression_multiple_props.snap	New snapshot covering multi-prop labeled-expression error via ph({a,b}).
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_ph_label_with_nested_plural.snap	Updates snapshot source location after test move.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_nested_labels.snap	Updates snapshot source location after test move.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_labeled_expression_multiple_props.snap	New snapshot covering multi-prop labeled-expression error in JSX explicit label.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_icu_with_labeled_expression_as_value.snap	New snapshot covering labeled-expression as ICU value.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_icu_with_labeled_expression_as_value_with_ph.snap	New snapshot covering ph({count: ...}) used as ICU value.
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_explicit_labels.snap	Updates snapshot source location and removes multi-prop case (now an error test).
crates/lingui_macro/tests/snapshots/labeled_expressions__jsx_explicit_labels_with_as_statement.snap	Updates snapshot source location after test move.
crates/lingui_macro/tests/snapshots/labeled_expressions__js_ph_with_non_object_arg.snap	New snapshot covering invalid ph(variable) usage in template literals.
crates/lingui_macro/tests/snapshots/labeled_expressions__js_ph_labels_in_tpl_literal.snap	Updates snapshot source location and removes multi-prop case (now an error test).
crates/lingui_macro/tests/snapshots/labeled_expressions__js_ph_labeled_expression_multiple_props.snap	New snapshot covering multi-prop labeled-expression error via ph({a,b}) in template literal.
crates/lingui_macro/tests/snapshots/labeled_expressions__js_labeled_expression_multiple_props.snap	New snapshot covering multi-prop labeled-expression error in template literal explicit label.
crates/lingui_macro/tests/snapshots/labeled_expressions__js_explicit_labels_in_tpl_literal.snap	Updates snapshot source location and removes multi-prop case (now an error test).
crates/lingui_macro/tests/snapshots/labeled_expressions__js_choice_labels_in_tpl_literal.snap	Updates snapshot source location after test move.
crates/lingui_macro/tests/snapshots/jsx_icu__with_value_index_in_source_order.snap	New regression snapshot for source-order ICU value index allocation.
crates/lingui_macro/tests/snapshots/jsx_icu__with_non_identifier_value_first.snap	New regression snapshot for ICU value when it appears first.
crates/lingui_macro/tests/snapshots/js_t__js_substitution_in_tpl_literal.snap	Snapshot updates reflecting new values ordering/allocation behavior.
crates/lingui_macro/tests/snapshots/js_t__js_custom_i18n_passed.snap	Snapshot updates reflecting new values ordering/allocation behavior.
crates/lingui_macro/tests/snapshots/js_icu__js_choices_may_contain_expressions.snap	Snapshot updates reflecting new values ordering/allocation behavior.

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[timofei-iatsenko]

@andrii-bodnar this one is ready