Support GraphQL variables in serialized requests instead of inlining input literals (upstream #559) #125

Context

Upstream issue kobylynskyi#559
asked for request parameters to be sent in the standard "variables" JSON section
({"query": "query($name:String){...}", "variables": {"name":"x"}}) instead of being
inlined into the query string. It was closed as a question with the reasoning that
servers accept inlined literals fine.

That reasoning misses real cases:

• Query complexity / depth limits: many servers (e.g. graphql-java's
  MaxQueryComplexityInstrumentation, Apollo Gateway, Hasura) compute complexity over
  the parsed document; inlined literals inflate the query text and defeat
  normalized-query caching / persisted queries, since every distinct value
  produces a different query document.
• Strict endpoints (the original reporter's ArangoDB Foxx case) that require proper
  variables separation.

Verification (this fork, current code)

Behavior is exactly as described in kobylynskyi#559 — variables are not supported:

• GraphQLRequestSerializer.buildQuery() inlines every input map entry via getEntry()
  (src/main/java/io/github/besi97/graphql/codegen/model/graphql/GraphQLRequestSerializer.java:100).
• jsonQuery() emits only {"query":"..."}; no variables key is ever produced (:139).
• "variables" appears nowhere in src/main or src/test.
• Generated request classes only carry Map<String, Object> input — no GraphQL type info
  is available at runtime, so variable definitions ($name: String!) cannot even be built.

Proposed design (full scope)

Variables become the default for freshly generated code; a codegen option
(serializeRequestInputAsVariables, default true) reverts to inlined literals.

Top-level operation arguments

• GraphQLOperationRequest: add default Map<String, String> getParamToGraphQLTypeMap()
  (arg name → GraphQL type, e.g. "id" -> "ID!"). Type map present ⇒ variables mode;
  absent ⇒ inline (backward compatible for hand-written requests).
• ParameterDefinition: add graphQLType; populate in InputValueDefinitionToParameterMapper
  via a new recursive AST→string helper in GraphQLTypeMapper ([ID!]!, etc.).
• Emit the map in java-lang/request.ftl + kotlin-lang/request.ftl.
• GraphQLParametrizedInput + both parametrized_input.ftls: add getInput() returning the
  raw field values (fields are private, no getters today) so nested input objects can be
  converted to JSON.
• Serializer: args render as $name; declarations prepended to the operation
  (query Op($x: Int!) {...}, also valid anonymously: query($x: Int)); body becomes
  {"query":"...","variables":{...}}. Values converted with a Jackson mapper copy using
  NON_NULL inclusion (enums → name, Input POJOs → Jackson, useObjectMapperForInputSerialization
  fields → JSON string). All-or-nothing fallback to inline if any non-null arg lacks a type.
• Batch (GraphQLRequests): merge declarations; dedupe identical name+type, rename conflicts
  ($name__2).

Nested field arguments in response projections

Fields like type Client { data(ID: Int!): Data! } currently inline 5 into
query clients { data(ID: 5) {...} } — same problem, one level down.

• GraphQLResponseProjection / GraphQLResponseField carry no arg-type info today;
  values only appear via ParametrizedInput.toString() (GraphQL literal syntax).
• Generated projections must expose per-field arg name → GraphQL type.
• Serializer walks the whole projection tree at serialization time, hoists every nested
  arg into a uniquely-named variable (same field with different args appears multiple
  times), and merges all declarations into the operation.
• This roughly doubles the change surface vs. top-level-only, but doing it halfway would
  leave a confusing mode where some args are variables and others are literals.

Tests

• GraphQLRequestSerializerTest: variables path, null skipping, enums/lists/nested inputs/
  custom scalars, anonymous ops, batch merge + conflict rename, fallback.
• GraphQLCodegenRequestTest: type map present by default / absent with option off;
  regenerate affected expected-classes/request/* (Java + Kotlin).

Docs

• README codegen-options table row for serializeRequestInputAsVariables.