Remove oneof validation from values of correct type (#4453)

Supersedes #4445
Fixes #4443

`VariablesInAllowedPositionRule` already validates this

Author: JoviDeCroock

src/validation/__tests__/ValuesOfCorrectTypeRule-test.ts

@@ -1094,22 +1094,6 @@ describe('Validate: Values of correct type', () => {
       ]);
     });
 
-    it('Exactly one nullable variable', () => {
-      expectErrors(`
-        query ($string: String) {
-          complicatedArgs {
-            oneOfArgField(oneOfArg: { stringField: $string })
-          }
-        }
-      `).toDeepEqual([
-        {
-          message:
-            'Variable "string" must be non-nullable to be used for OneOf Input Object "OneOfInput".',
-          locations: [{ line: 4, column: 37 }],
-        },
-      ]);
-    });
-
     it('More than one field', () => {
       expectErrors(`
         {

src/validation/__tests__/VariablesInAllowedPositionRule-test.ts

@@ -370,6 +370,16 @@ describe('Validates OneOf Input Objects', () => {
     `);
   });
 
+  it('Undefined variable in oneOf input object', () => {
+    expectErrors(`
+      {
+        complicatedArgs {
+          oneOfArgField(oneOfArg: { stringField: $undefinedVariable })
+        }
+      }
+    `).toDeepEqual([]);
+  });
+
   it('Forbids one nullable variable', () => {
     expectErrors(`
       query ($string: String) {

src/validation/rules/ValuesOfCorrectTypeRule.ts

@@ -82,13 +82,7 @@ export function ValuesOfCorrectTypeRule(
       }
 
       if (type.isOneOf) {
-        validateOneOfInputObject(
-          context,
-          node,
-          type,
-          fieldNodeMap,
-          variableDefinitions,
-        );
+        validateOneOfInputObject(context, node, type, fieldNodeMap);
       }
     },
     ObjectField(node) {
@@ -185,7 +179,6 @@ function validateOneOfInputObject(
   node: ObjectValueNode,
   type: GraphQLInputObjectType,
   fieldNodeMap: ObjMap<ObjectFieldNode>,
-  variableDefinitions: { [key: string]: VariableDefinitionNode },
 ): void {
   const keys = Object.keys(fieldNodeMap);
   const isNotExactlyOneField = keys.length !== 1;
@@ -202,29 +195,12 @@ function validateOneOfInputObject(
 
   const value = fieldNodeMap[keys[0]]?.value;
   const isNullLiteral = !value || value.kind === Kind.NULL;
-  const isVariable = value?.kind === Kind.VARIABLE;
 
   if (isNullLiteral) {
     context.reportError(
       new GraphQLError(`Field "${type.name}.${keys[0]}" must be non-null.`, {
         nodes: [node],
       }),
     );
-    return;
-  }
-
-  if (isVariable) {
-    const variableName = value.name.value;
-    const definition = variableDefinitions[variableName];
-    const isNullableVariable = definition.type.kind !== Kind.NON_NULL_TYPE;
-
-    if (isNullableVariable) {
-      context.reportError(
-        new GraphQLError(
-          `Variable "${variableName}" must be non-nullable to be used for OneOf Input Object "${type.name}".`,
-          { nodes: [node] },
-        ),
-      );
-    }
   }
 }