Non-deterministic HashMap iteration affects build cache reliability #42

Problem

MappingConfig uses HashMap and HashSet extensively. When these collections are iterated during code generation, the order can vary between JVM runs due to hash randomization.

This causes non-deterministic output when multiple regex patterns in customAnnotationsMapping match the same type.

Example

Given this configuration:

customAnnotationsMapping = {
  ".*TO$" -> ["@Auditable"],      // matches "ProductTO"
  "Product.*" -> ["@Cached"]      // also matches "ProductTO"
}

When generating ProductTO, both regex patterns match. Depending on HashMap iteration order:

Run 1: .*TO$ first, then Product.*

@Auditable
@Cached
public class ProductTO { ... }

Run 2: Product.* first, then .*TO$

@Cached
@Auditable
public class ProductTO { ... }

The annotations are semantically identical, but byte-for-byte different.

Impact on Build Caching

Cache hits: Work correctly — Gradle retrieves the exact cached output regardless of HashMap ordering.

Cache misses: Can produce different outputs on each run, making the cache unreliable when:

• Cache is frequently cleared
• Multiple developers share a cache
• Byte-for-byte reproducibility is required

Options to Fix

Option 1: Sort during iteration

Sort map entries by key during code generation:

map.entrySet().stream()
    .sorted(Map.Entry.comparingByKey())
    .forEach(entry -> { ... });

Option 2: Use sorted collections

Replace HashMap/HashSet with TreeMap/TreeSet in MappingConfig:

private Map<String, List<String>> customAnnotationsMapping = new TreeMap<>();

Option 3: Sort before code generation

Collect items into sorted lists before generating code.

Affected Code

• src/main/java/io/github/besi97/graphql/codegen/mapper/AnnotationsMapper.java:153 — iterates customAnnotationsMapping.entrySet()
• src/main/java/io/github/besi97/graphql/codegen/model/MappingConfig.java — uses HashMap and HashSet for configuration properties
• Additional iteration points throughout the codebase (25 occurrences found)