Edge Cases

Header File Deleted

Scenario: .hrl file removed from project

Handling:

1. prune/5 finds header with no incoming edges
2. Delete vertex
3. Files including it will fail compilation (caught later)

Source File Deleted

Scenario: .erl file removed

Handling:

1. prune/5 finds source not in current list
2. Check if in app paths
3. Delete source vertex
4. Find and delete associated artifact (.beam)
5. Mark dirty

Timestamp Regression

Scenario: File restored from backup with older timestamp

Behavior: Change not detected

Limitation: Timestamp-based system can't detect regression

Workaround: Force rebuild (rebar3 clean && rebar3 compile)

Parse Transform Affects All Files

Scenario: Parse transform modified

Handling:

• Compiler (rebar_compiler_erl) detects parse transform change
• Returns all files as needing compilation
• DAG not specifically involved

Multiple Artifacts from One Source

Scenario: .mib generates .bin and .hrl

Handling:

• Call store_artifact/4 twice
• Two artifact vertices
• Two artifact edges to same source

Concurrent Builds

Scenario: Two rebar3 processes running simultaneously

Risk: DAG file corruption

Mitigation: None built-in; avoid concurrent builds

Large Projects

Performance: DAG operations scale linearly

Optimization: Parallel dependency scanning

Typical: 1000+ files handled efficiently