Edge Cases

Parse Transform Recompilation

Scenario: Parse transform source changed

Behavior: ALL files recompiled (parse transforms affect all files)

Detection: needed_files/6 checks parse transform timestamps

ERL_OPTS Change

Condition: Compiler options changed in rebar.config

Behavior: Affected files recompiled

Detection: DAG compares stored options with current options

Include File Modified

Condition: .hrl file changed

Behavior: All files including it (directly or transitively) recompiled

Detection: DAG timestamp propagation

Generated Source Files

Scenario: .yrl generates .erl, which must then compile to .beam

Handling:

1. rebar_compiler_yrl runs first, generates .erl
2. rebar_compiler_erl runs second, finds generated .erl
3. Compiles generated .erl to .beam

Critical: Compiler order matters

Parallel Compilation Failures

Scenario: One of parallel compilations fails

Behavior:

• Worker reports error
• Main process collects error
• Compilation aborts with error

Impact: Some files may be partially compiled

Large Projects

Optimization: Parallel compilation significantly speeds up builds

Example: 100 independent .erl files

• Sequential: ~100 seconds
• Parallel (8 cores): ~15 seconds