fix: report line-local columns for VM events

[wuyua9]

Summary

• track the 0-indexed source column alongside each bytecode line-table entry
• preserve that column when lowering bytecode to compact form
• use the recorded line-local column for SendEvent source locations while keeping start/end offsets unchanged

Tests

• rustfmt --edition 2024 baml_language/crates/baml_compiler2_emit/src/emit.rs baml_language/crates/bex_vm/src/vm.rs baml_language/crates/bex_vm_types/src/bytecode.rs
• git diff --check
• Not run: cargo test -p bex_vm_types line_table_translated --manifest-path baml_language/Cargo.toml cannot link in this local macOS environment because xcrun fails to load the installed CommandLineTools libxcrun.dylib as arm64/arm64e while compiling build scripts.

Summary by CodeRabbit

• Bug Fixes
  • Enhanced source location tracking to include precise column offsets alongside line numbers in debug information, enabling more accurate error reporting and debugging capabilities.

[vercel]

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[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: 04539885-9dcb-4ed4-903a-bfcae2768031

📥 Commits

Reviewing files that changed from the base of the PR and between 066b6cb and 3596629.

📒 Files selected for processing (3)

• baml_language/crates/baml_compiler2_emit/src/emit.rs
• baml_language/crates/bex_vm/src/vm.rs
• baml_language/crates/bex_vm_types/src/bytecode.rs

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📝 Walkthrough

Walkthrough

This PR extends debug source mapping to track column offsets alongside line numbers. The compiler now computes 0-indexed columns during line-table generation, stores them in bytecode entries, propagates them through compact bytecode, and uses them in VM event emission.

Changes

Column Offsets in Source Location Tracking

Layer / File(s)	Summary
LineTableEntry struct definition baml_language/crates/bex_vm_types/src/bytecode.rs	New column: u32 field added to LineTableEntry for per-bytecode column metadata.
Line and column computation helpers baml_language/crates/baml_compiler2_emit/src/emit.rs	offset_to_line_column and span_to_line_column replace line-only helpers, computing columns from source offsets while preserving prior normalization and fallback logic.
LineTableEntry emission with column baml_language/crates/baml_compiler2_emit/src/emit.rs	Line-table emission updated to destructure (line, column) tuples and populate both fields in LineTableEntry structs.
Bytecode compact translation of column baml_language/crates/bex_vm_types/src/bytecode.rs	Bytecode::lower_to_compact() now copies the new column field when translating line-table entries.
VM event emission with column baml_language/crates/bex_vm/src/vm.rs	SendEvent opcode handling updated to use entry.column from bytecode instead of deriving it from span offset.
Line table translation test updates baml_language/crates/bex_vm_types/src/bytecode.rs	Test constructs LineTableEntry with column values and asserts correct column propagation through compaction.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A column's found alongside each line,
From source offsets, the coords align,
Through bytecode flows, the metadata glides,
Till VM events show where error resides! ✨

🚥 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 concisely summarizes the main change: adding column information to VM event source locations.
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 unit tests (beta)

• Create PR with unit tests

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