Eliminate circular dependency in validation rules (#1263)

`validation/validate.js` depends on all of the rules, and all of the
rules depend on `ValidationContext`, which was previously exported by
`validation/validate.js`.

This moves `ValidationContext` out of `validate.js` to resolve this.

Circular dependencies are fine, but they tend to slow down flow, since
it moves more work to the merging phase, and the merging phase isn't as
fast as the inference phase. As a result, this should make flow
marginally faster.

This does have a minor breaking change: `graphql/validatation/validate`
no longer exports `ValidationContext`, but `graphql/validation` still
does. I can add an export to `validate.js` to preserve that behavior,
but it's a minor change to a non-public API, and graphql-js has broken
these things in the past.

src/utilities/isValidLiteralValue.js

@@ -15,7 +15,7 @@ import { visit, visitWithTypeInfo } from '../language/visitor';
 import type { GraphQLInputType } from '../type/definition';
 import { GraphQLSchema } from '../type/schema';
 import { ValuesOfCorrectType } from '../validation/rules/ValuesOfCorrectType';
-import { ValidationContext } from '../validation/validate';
+import ValidationContext from '../validation/ValidationContext';
 
 /**
  * Utility which determines if a value literal node is valid for an input type.

src/validation/ValidationContext.js

@@ -0,0 +1,221 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import type { ObjMap } from '../jsutils/ObjMap';
+import { GraphQLError } from '../error';
+import { visit, visitWithTypeInfo } from '../language/visitor';
+import { Kind } from '../language/kinds';
+import type {
+  DocumentNode,
+  OperationDefinitionNode,
+  VariableNode,
+  SelectionSetNode,
+  FragmentSpreadNode,
+  FragmentDefinitionNode,
+} from '../language/ast';
+import { GraphQLSchema } from '../type/schema';
+import type {
+  GraphQLInputType,
+  GraphQLOutputType,
+  GraphQLCompositeType,
+  GraphQLField,
+  GraphQLArgument,
+} from '../type/definition';
+import type { GraphQLDirective } from '../type/directives';
+import { TypeInfo } from '../utilities/TypeInfo';
+
+type NodeWithSelectionSet = OperationDefinitionNode | FragmentDefinitionNode;
+type VariableUsage = { node: VariableNode, type: ?GraphQLInputType };
+
+/**
+ * An instance of this class is passed as the "this" context to all validators,
+ * allowing access to commonly useful contextual information from within a
+ * validation rule.
+ */
+export default class ValidationContext {
+  _schema: GraphQLSchema;
+  _ast: DocumentNode;
+  _typeInfo: TypeInfo;
+  _errors: Array<GraphQLError>;
+  _fragments: ObjMap<FragmentDefinitionNode>;
+  _fragmentSpreads: Map<SelectionSetNode, $ReadOnlyArray<FragmentSpreadNode>>;
+  _recursivelyReferencedFragments: Map<
+    OperationDefinitionNode,
+    $ReadOnlyArray<FragmentDefinitionNode>,
+  >;
+  _variableUsages: Map<NodeWithSelectionSet, $ReadOnlyArray<VariableUsage>>;
+  _recursiveVariableUsages: Map<
+    OperationDefinitionNode,
+    $ReadOnlyArray<VariableUsage>,
+  >;
+
+  constructor(
+    schema: GraphQLSchema,
+    ast: DocumentNode,
+    typeInfo: TypeInfo,
+  ): void {
+    this._schema = schema;
+    this._ast = ast;
+    this._typeInfo = typeInfo;
+    this._errors = [];
+    this._fragmentSpreads = new Map();
+    this._recursivelyReferencedFragments = new Map();
+    this._variableUsages = new Map();
+    this._recursiveVariableUsages = new Map();
+  }
+
+  reportError(error: GraphQLError): void {
+    this._errors.push(error);
+  }
+
+  getErrors(): $ReadOnlyArray<GraphQLError> {
+    return this._errors;
+  }
+
+  getSchema(): GraphQLSchema {
+    return this._schema;
+  }
+
+  getDocument(): DocumentNode {
+    return this._ast;
+  }
+
+  getFragment(name: string): ?FragmentDefinitionNode {
+    let fragments = this._fragments;
+    if (!fragments) {
+      this._fragments = fragments = this.getDocument().definitions.reduce(
+        (frags, statement) => {
+          if (statement.kind === Kind.FRAGMENT_DEFINITION) {
+            frags[statement.name.value] = statement;
+          }
+          return frags;
+        },
+        Object.create(null),
+      );
+    }
+    return fragments[name];
+  }
+
+  getFragmentSpreads(
+    node: SelectionSetNode,
+  ): $ReadOnlyArray<FragmentSpreadNode> {
+    let spreads = this._fragmentSpreads.get(node);
+    if (!spreads) {
+      spreads = [];
+      const setsToVisit: Array<SelectionSetNode> = [node];
+      while (setsToVisit.length !== 0) {
+        const set = setsToVisit.pop();
+        for (let i = 0; i < set.selections.length; i++) {
+          const selection = set.selections[i];
+          if (selection.kind === Kind.FRAGMENT_SPREAD) {
+            spreads.push(selection);
+          } else if (selection.selectionSet) {
+            setsToVisit.push(selection.selectionSet);
+          }
+        }
+      }
+      this._fragmentSpreads.set(node, spreads);
+    }
+    return spreads;
+  }
+
+  getRecursivelyReferencedFragments(
+    operation: OperationDefinitionNode,
+  ): $ReadOnlyArray<FragmentDefinitionNode> {
+    let fragments = this._recursivelyReferencedFragments.get(operation);
+    if (!fragments) {
+      fragments = [];
+      const collectedNames = Object.create(null);
+      const nodesToVisit: Array<SelectionSetNode> = [operation.selectionSet];
+      while (nodesToVisit.length !== 0) {
+        const node = nodesToVisit.pop();
+        const spreads = this.getFragmentSpreads(node);
+        for (let i = 0; i < spreads.length; i++) {
+          const fragName = spreads[i].name.value;
+          if (collectedNames[fragName] !== true) {
+            collectedNames[fragName] = true;
+            const fragment = this.getFragment(fragName);
+            if (fragment) {
+              fragments.push(fragment);
+              nodesToVisit.push(fragment.selectionSet);
+            }
+          }
+        }
+      }
+      this._recursivelyReferencedFragments.set(operation, fragments);
+    }
+    return fragments;
+  }
+
+  getVariableUsages(node: NodeWithSelectionSet): $ReadOnlyArray<VariableUsage> {
+    let usages = this._variableUsages.get(node);
+    if (!usages) {
+      const newUsages = [];
+      const typeInfo = new TypeInfo(this._schema);
+      visit(
+        node,
+        visitWithTypeInfo(typeInfo, {
+          VariableDefinition: () => false,
+          Variable(variable) {
+            newUsages.push({ node: variable, type: typeInfo.getInputType() });
+          },
+        }),
+      );
+      usages = newUsages;
+      this._variableUsages.set(node, usages);
+    }
+    return usages;
+  }
+
+  getRecursiveVariableUsages(
+    operation: OperationDefinitionNode,
+  ): $ReadOnlyArray<VariableUsage> {
+    let usages = this._recursiveVariableUsages.get(operation);
+    if (!usages) {
+      usages = this.getVariableUsages(operation);
+      const fragments = this.getRecursivelyReferencedFragments(operation);
+      for (let i = 0; i < fragments.length; i++) {
+        Array.prototype.push.apply(
+          usages,
+          this.getVariableUsages(fragments[i]),
+        );
+      }
+      this._recursiveVariableUsages.set(operation, usages);
+    }
+    return usages;
+  }
+
+  getType(): ?GraphQLOutputType {
+    return this._typeInfo.getType();
+  }
+
+  getParentType(): ?GraphQLCompositeType {
+    return this._typeInfo.getParentType();
+  }
+
+  getInputType(): ?GraphQLInputType {
+    return this._typeInfo.getInputType();
+  }
+
+  getParentInputType(): ?GraphQLInputType {
+    return this._typeInfo.getParentInputType();
+  }
+
+  getFieldDef(): ?GraphQLField<*, *> {
+    return this._typeInfo.getFieldDef();
+  }
+
+  getDirective(): ?GraphQLDirective {
+    return this._typeInfo.getDirective();
+  }
+
+  getArgument(): ?GraphQLArgument {
+    return this._typeInfo.getArgument();
+  }
+}

src/validation/index.js

@@ -7,7 +7,11 @@
  * @flow strict
  */
 
-export { validate, ValidationContext } from './validate';
+export { validate } from './validate';
+
+// https://github.com/tc39/proposal-export-default-from
+import ValidationContext from './ValidationContext';
+export { ValidationContext };
 
 export { specifiedRules } from './specifiedRules';
 

src/validation/rules/ExecutableDefinitions.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import { Kind } from '../../language/kinds';
 import type { ASTVisitor } from '../../language/visitor';

src/validation/rules/FieldsOnCorrectType.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import suggestionList from '../../jsutils/suggestionList';
 import quotedOrList from '../../jsutils/quotedOrList';

src/validation/rules/FragmentsOnCompositeTypes.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import { print } from '../../language/printer';
 import type { ASTVisitor } from '../../language/visitor';

src/validation/rules/KnownArgumentNames.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 import suggestionList from '../../jsutils/suggestionList';

src/validation/rules/KnownDirectives.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import find from '../../jsutils/find';
 import { Kind } from '../../language/kinds';

src/validation/rules/KnownFragmentNames.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 

src/validation/rules/KnownTypeNames.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import suggestionList from '../../jsutils/suggestionList';
 import quotedOrList from '../../jsutils/quotedOrList';

src/validation/rules/LoneAnonymousOperation.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import { Kind } from '../../language/kinds';
 import type { ASTVisitor } from '../../language/visitor';

src/validation/rules/NoFragmentCycles.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { FragmentDefinitionNode } from '../../language/ast';
 import type { ASTVisitor } from '../../language/visitor';

src/validation/rules/NoUndefinedVariables.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 

src/validation/rules/NoUnusedFragments.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 

src/validation/rules/NoUnusedVariables.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 

src/validation/rules/OverlappingFieldsCanBeMerged.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import find from '../../jsutils/find';
 import type { ObjMap } from '../../jsutils/ObjMap';

src/validation/rules/PossibleFragmentSpreads.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { ASTVisitor } from '../../language/visitor';
 import { doTypesOverlap } from '../../utilities/typeComparators';

src/validation/rules/ProvidedNonNullArguments.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import keyMap from '../../jsutils/keyMap';
 import { isNonNullType } from '../../type/definition';

src/validation/rules/ScalarLeafs.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { FieldNode } from '../../language/ast';
 import { getNamedType, isLeafType } from '../../type/definition';

src/validation/rules/SingleFieldSubscriptions.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import type { ValidationContext } from '../index';
+import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { OperationDefinitionNode } from '../../language/ast';
 import type { ASTVisitor } from '../../language/visitor';