Error Conditions

Circular Dependencies Detected

Condition: Dependency graph contains one or more cycles

Detection: digraph_utils:is_acyclic/1 returns false

Error Format:

{cycles, [[<<"app1">>, <<"app2">>, <<"app3">>], [<<"app4">>, <<"app5">>]]}

Error Message (from rebar_prv_install_deps):

Dependency cycle(s) detected:
applications: app1 app2 app3 depend on each other
applications: app4 app5 depend on each other

Example Cycle:

app1 depends on app2
app2 depends on app3
app3 depends on app1

Recovery: None; must break the cycle in dependencies

Common Causes:

• Circular applications lists in .app files
• Circular deps in rebar.config files
• Mix of runtime and build-time circular dependencies

Topological Sort Failed (Non-Cyclic)

Condition: Graph is acyclic but sort fails anyway

Error Format:

{error, no_sort}

Likelihood: Very rare; theoretical edge case

Possible Causes:

• Erlang digraph library issue
• Malformed graph structure

Recovery: Report as bug

Missing Dependency in Graph

Condition: Application references dependency not in graph

Behavior: Not an error at this stage

Handling:

• Digraph adds vertex automatically for missing deps
• Vertex exists but no app info record associated
• names_to_apps/2 skips missing apps
• Error likely caught in earlier stage (dependency resolution)