Remove the unused res.iflet encoding of if let

[cknitt]

Stacked on #8740. Resolves the res.iflet item of #8624 by removing the encoding rather than giving it a node.

if let has been in the syntax since at least 2020 (as ns.iflet, renamed in #5862), but the parser always rejects it with a syntax error: "If-let is currently highly experimental. Use a regular switch with pattern matching instead", followed by the equivalent switch. There's no flag that enables it, and the formatter refuses files with syntax errors. Still, the parser encoded if let as a switch marked with res.iflet and @warning("-4"), and the viewer, printer and comment table carried code to print it back. The printer tests for it had already been commented out.

Changes

• Parser: if let is still parsed for recovery and still reported with the same error and suggestion, but as a plain switch without the two attributes.
• Viewer:
  • removed has_if_let_attribute, is_if_let_expr, the IfLet case of the if-chain condition (the if_condition_kind type goes away), filter_fragile_match_attributes, and res.iflet in is_parsing_attr;
  • without its res.iflet exception, has_attributes meant "has any attribute", so it's inlined at its callers.
• Printer and comment table: removed the if let cases.
• Tests: the commented-out if let printer tests are removed; the error test parsing/errors/expressions/ifLet.res keeps covering the message.

Behavior

• The if let error message is unchanged; the error test's snapshot only shows the recovered tree without the attributes.
• filter_fragile_match_attributes also applied to ordinary if expressions, so the formatter dropped a @warning("-4") written on an if. It's now kept.
• Formatting of the repo's .res/.resi files is unchanged.

Tests

• printer/expr/if.res: @warning("-4") on an if expression.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.00%. Comparing base (18f3233) to head (121f150).

Files with missing lines	Patch %	Lines
compiler/syntax/src/res_printer.ml	87.50%	2 Missing ⚠️
compiler/syntax/src/res_parsetree_viewer.ml	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8741      +/-   ##
==========================================
+ Coverage   79.97%   80.00%   +0.02%     
==========================================
  Files         464      464              
  Lines       63232    63149      -83     
==========================================
- Hits        50571    50523      -48     
+ Misses      12661    12626      -35     

Files with missing lines	Coverage Δ
compiler/syntax/src/res_comments_table.ml	91.25% <ø> (+2.12%)	⬆️
compiler/syntax/src/res_core.ml	91.95% <100.00%> (-0.01%)	⬇️
compiler/syntax/src/res_parens.ml	83.70% <100.00%> (-0.07%)	⬇️
compiler/syntax/src/res_parsetree_viewer.ml	94.00% <0.00%> (+0.99%)	⬆️
compiler/syntax/src/res_printer.ml	93.54% <87.50%> (+0.02%)	⬆️

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commit: 121f150

[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-08T14:29:52.861143Z	7a64333	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

Reviewed commit: 7a6433366b

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