baml_language: add duplicate parameter error

[codeshaunted]

Summary by CodeRabbit

• Bug Fixes

  • Compiler now detects and reports duplicate parameter names in both functions and lambda expressions. This improved validation catches parameter naming conflicts early, preventing potential runtime issues.

• Tests

  • Added comprehensive test coverage for duplicate parameter detection to ensure the validation works correctly for both duplicate and distinct parameter names.

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Project	Deployment	Actions	Updated (UTC)
beps	Ready	Preview, Comment	May 12, 2026 7:40pm
promptfiddle	Ready	Preview, Comment	May 12, 2026 7:40pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 1a4f2664-db01-4558-a837-e718c5653a5b

📥 Commits

Reviewing files that changed from the base of the PR and between 790a8bd and 14d2a17.

📒 Files selected for processing (2)

• baml_language/crates/baml_compiler2_hir/src/builder.rs
• baml_language/crates/baml_tests/src/compiler2_hir.rs

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📝 Walkthrough

Walkthrough

This PR adds duplicate function and lambda parameter name detection to the compiler's semantic analysis. A new helper emits diagnostics when parameter lists contain repeated names, integrated into both lambda and function processing during HIR construction with comprehensive test coverage.

Changes

Duplicate Parameter Detection

Layer / File(s)	Summary
Duplicate detection implementation and integration baml_language/crates/baml_compiler2_hir/src/builder.rs	New emit_duplicate_param_diagnostics helper maps parameter names to their definition sites and delegates duplicate reporting to existing emit_duplicate_diagnostics. Method is called in walk_lambda_expr and lower_function to diagnose duplicate parameter names in both lambdas and regular functions.
Test coverage for duplicate parameter detection baml_language/crates/baml_tests/src/compiler2_hir.rs	One test verifies duplicate function parameters across positional/defaulted combinations emit exactly one DuplicateDefinition diagnostic with two Parameter-kind sites. Regression test confirms distinct parameter names produce no diagnostics.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A rabbit hops through parameter lists with glee,
Spotting doubles—twice the name, but errors we see!
Lambda and function both now check with care,
Duplicate params caught, diagnostics laid bare! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main change: adding duplicate parameter error detection for both functions and lambdas in the BAML compiler.
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 avery/dup-params-error

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[github-actions]

Binary size checks failed

❌ 1 violations · ✅ 6 passed

⚠️ Please fix the size gate issues or acknowledge them by updating baselines.

	Artifact	Platform	Gzip	Baseline	Delta	Status
❌	bridge_cffi	Linux	6.6 MB	6.4 MB	+152.2 KB (+2.4%)	FAIL
✅	bridge_cffi-stripped	Linux	5.6 MB	5.7 MB	-52.1 KB (-0.9%)	OK
✅	bridge_cffi	macOS	5.4 MB	5.1 MB	+325.7 KB (+6.4%)	OK
✅	bridge_cffi-stripped	macOS	4.6 MB	4.7 MB	-52.8 KB (-1.1%)	OK
✅	bridge_cffi	Windows	5.4 MB	5.1 MB	+284.0 KB (+5.6%)	OK
✅	bridge_cffi-stripped	Windows	4.7 MB	4.7 MB	+21.5 KB (+0.5%)	OK
✅	bridge_wasm	WASM	3.6 MB	3.5 MB	+43.2 KB (+1.2%)	OK

Details & how to fix

Violations:

• bridge_cffi (Linux) gzip_bytes: 6.6 MB exceeds limit of 6.5 MB (exceeded by +87.9 KB, policy: max_gzip_bytes)

Add/update baselines:

.ci/size-gate/x86_64-unknown-linux-gnu.toml:

[artifacts.bridge_cffi]
file_bytes = 17655608
stripped_bytes = 17655600
gzip_bytes = 6587944

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Generated by cargo size-gate · workflow run