Edge Cases

Empty Application List

Input: []

Behavior: Returns {ok, []}

Use Case: No applications to compile

Single Application

Input: Single app with no dependencies

Behavior: Returns {ok, [App]}

Graph: Single vertex, no edges

Application Depends on Itself

Behavior: Creates self-loop in graph

Detection: Caught by cycle detection

Error: Reported as single-app cycle

Transitive Dependencies

Scenario:

my_app → lib_a → lib_b → lib_c

Behavior: All transitive dependencies included in graph

Ordering: [lib_c, lib_b, lib_a, my_app]

Why It Works: Each level adds its dependencies to graph

Diamond Dependency Pattern

Scenario:

my_app → [lib_a, lib_b]
lib_a → lib_common
lib_b → lib_common

Behavior: lib_common appears once in sorted output

Ordering: [lib_common, lib_a, lib_b, my_app] (or lib_b before lib_a)

Note: Order between lib_a and lib_b is arbitrary (no dependency between them)

Dependency Referenced but Not Present

Scenario: App lists dependency that wasn't resolved

Example:

% my_app.app.src
{applications, [kernel, stdlib, missing_lib]}

Behavior:

• Vertex created for missing_lib
• No corresponding app info
• names_to_apps skips it
• Won't appear in final sorted list
• Compilation will likely fail later

OTP Applications in Dependency List

Scenario: Dependencies include OTP apps like kernel, stdlib

Behavior: Included in graph but not in final compile list

Reason: OTP apps aren't in the input app list, so names_to_apps skips them

Example:

Input: [my_app]
my_app depends on: [kernel, stdlib, jsx]

Graph vertices: my_app, kernel, stdlib, jsx
Sorted: [kernel, stdlib, jsx, my_app]
names_to_apps result: [jsx, my_app]  % kernel, stdlib not in input

Multiple Independent Apps

Scenario: Multiple apps with no inter-dependencies

Example:

app1 → [kernel, stdlib]
app2 → [kernel, stdlib]
app3 → [kernel, stdlib]

Behavior: Arbitrary order between app1, app2, app3

Ordering: Any permutation valid, e.g., [app1, app2, app3] or [app3, app1, app2]