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Replace `BiMap` with plain maps

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Refactor
Clarity
Mostly clear
Activity status
Active
Tech stack
java, kotlin
Domain
backend-api-design

Research direction

Start by tracing how SchemaClassScanner builds TypeClassDictionary and how SchemaParser uses it in both directions, including resolver return types. Then review SchemaParserDictionary.getDictionary() and the graphql-spring-boot call to builder.dictionary(); done means duplicate classes produce a SchemaClassScannerError naming the class and types, the new map-returning method is used without breaking the old API, and BiMap can be removed in a later major release.

Written by the indexing model from the issue text.

Description

graphql.kickstart.tools.util.BiMap is a copy of Guava's BiMap we added when we dropped Guava (661769e). Neither Java nor Kotlin has a bidirectional map, so it stuck around. After #851 it doesn't really pull its weight anymore.

Where it's used:

  • SchemaClassScanner builds a BiMap<TypeDefinition, JavaType> (TypeClassDictionary). SchemaParser reads it both ways: dictionary[definition] for enum classes and dictionary.inverse() for InterfaceTypeResolver and UnionTypeResolver.
  • BiMap#put throwing value already present is the only thing that enforces one class per output type. It shows up as Error creating bimap of type => class, which isn't a very helpful message. It also catches classes found through resolver return types, not just dictionary entries, so a replacement needs an explicit check.
  • SchemaParserDictionary stores a plain map since #851. getDictionary() still returns a BiMap for backwards compatibility (graphql-spring-boot calls builder.dictionary(dictionary.getDictionary())), but its inverse() only keeps the first name when several input types share a class.

Proposal:

  1. Internally, use two plain maps plus an explicit duplicate check that throws a SchemaClassScannerError naming the class and the types. No API change.
typeToClass.entries.groupBy({ it.value }, { it.key })
    .filterValues { it.size > 1 }
    .forEach { (clazz, types) -> throw SchemaClassScannerError("...") }
val classToType = typeToClass.entries.associate { (type, clazz) -> clazz to type }
  1. Add a replacement for getDictionary() that returns Map<String, Class<*>> under a new name, and deprecate getDictionary(). Changing the return type in place would break binary compatibility.
  2. Switch graphql-spring-boot to the new method.
  3. Remove BiMap in the next major.
Dominant language
Kotlin
Stars
824
Forks
175
Avg merge
2d 5h
Merged PRs (30d)
52

Getting set up

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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