Add 'Symbol.toStringTag' into every publicly exported class

.eslintrc.yml

@@ -22,6 +22,7 @@ rules:
 
   internal-rules/only-ascii: error
   internal-rules/no-dir-import: error
+  internal-rules/require-to-string-tag: off
 
   ##############################################################################
   # `eslint-plugin-istanbul` rule list based on `v0.1.2`
@@ -610,8 +611,12 @@ overrides:
       '@typescript-eslint/space-before-function-paren': off
       '@typescript-eslint/space-infix-ops': off
       '@typescript-eslint/type-annotation-spacing': off
+  - files: 'src/**'
+    rules:
+      internal-rules/require-to-string-tag: error
   - files: 'src/**/__*__/**'
     rules:
+      internal-rules/require-to-string-tag: off
       node/no-unpublished-import: [error, { allowModules: ['chai', 'mocha'] }]
       import/no-restricted-paths: off
       import/no-extraneous-dependencies: [error, { devDependencies: true }]

resources/eslint-internal-rules/index.js

@@ -2,10 +2,12 @@
 
 const onlyASCII = require('./only-ascii.js');
 const noDirImport = require('./no-dir-import.js');
+const requireToStringTag = require('./require-to-string-tag.js');
 
 module.exports = {
   rules: {
     'only-ascii': onlyASCII,
     'no-dir-import': noDirImport,
+    'require-to-string-tag': requireToStringTag,
   },
 };

resources/eslint-internal-rules/require-to-string-tag.js

@@ -0,0 +1,37 @@
+'use strict';
+
+module.exports = function requireToStringTag(context) {
+  const sourceCode = context.getSourceCode();
+
+  return {
+    'ExportNamedDeclaration > ClassDeclaration': (classNode) => {
+      const properties = classNode.body.body;
+      if (properties.some(isToStringTagProperty)) {
+        return;
+      }
+
+      const jsDoc = context.getJSDocComment(classNode)?.value;
+      // FIXME: use proper TSDoc parser instead of includes once we fix TSDoc comments
+      if (jsDoc?.includes('@internal') === true) {
+        return;
+      }
+
+      context.report({
+        node: classNode,
+        message:
+          'All classes in public API required to have [Symbol.toStringTag] method',
+      });
+    },
+  };
+
+  function isToStringTagProperty(propertyNode) {
+    if (
+      propertyNode.type !== 'MethodDefinition' ||
+      propertyNode.kind !== 'get'
+    ) {
+      return false;
+    }
+    const keyText = sourceCode.getText(propertyNode.key);
+    return keyText === 'Symbol.toStringTag';
+  }
+};

src/language/__tests__/lexer-test.ts

@@ -114,8 +114,13 @@ describe('Lexer', () => {
     });
   });
 
-  it('can be JSON.stringified, util.inspected or jsutils.inspect', () => {
-    const token = lexOne('foo');
+  it('can be Object.toStringified, JSON.stringified, or jsutils.inspected', () => {
+    const lexer = new Lexer(new Source('foo'));
+    const token = lexer.advance();
+
+    expect(Object.prototype.toString.call(lexer)).to.equal('[object Lexer]');
+
+    expect(Object.prototype.toString.call(token)).to.equal('[object Token]');
     expect(JSON.stringify(token)).to.equal(
       '{"kind":"Name","value":"foo","line":1,"column":1}',
     );

src/language/__tests__/parser-test.ts

@@ -372,11 +372,12 @@ describe('Parser', () => {
     expect(() => parse(document)).to.throw('Syntax Error');
   });
 
-  it('contains location information that only stringifies start/end', () => {
-    const result = parse('{ id }');
+  it('contains location that can be Object.toStringified, JSON.stringified, or jsutils.inspected', () => {
+    const { loc } = parse('{ id }');
 
-    expect(JSON.stringify(result.loc)).to.equal('{"start":0,"end":6}');
-    expect(inspect(result.loc)).to.equal('{ start: 0, end: 6 }');
+    expect(Object.prototype.toString.call(loc)).to.equal('[object Location]');
+    expect(JSON.stringify(loc)).to.equal('{"start":0,"end":6}');
+    expect(inspect(loc)).to.equal('{ start: 0, end: 6 }');
   });
 
   it('contains references to source', () => {

src/language/ast.ts

@@ -42,6 +42,10 @@ export class Location {
   toJSON(): { start: number; end: number } {
     return { start: this.start, end: this.end };
   }
+
+  get [Symbol.toStringTag]() {
+    return 'Location';
+  }
 }
 
 /**
@@ -121,6 +125,10 @@ export class Token {
       column: this.column,
     };
   }
+
+  get [Symbol.toStringTag]() {
+    return 'Token';
+  }
 }
 
 /**

src/language/lexer.ts

@@ -79,6 +79,10 @@ export class Lexer {
     }
     return token;
   }
+
+  get [Symbol.toStringTag]() {
+    return 'Lexer';
+  }
 }
 
 /**

src/utilities/TypeInfo.ts

@@ -292,6 +292,10 @@ export class TypeInfo {
         break;
     }
   }
+
+  get [Symbol.toStringTag]() {
+    return 'TypeInfo';
+  }
 }
 
 type GetFieldDefFn = (

src/utilities/__tests__/TypeInfo-test.ts

@@ -15,6 +15,14 @@ import { TypeInfo, visitWithTypeInfo } from '../TypeInfo';
 import { testSchema } from '../../validation/__tests__/harness';
 
 describe('TypeInfo', () => {
+  it('can be Object.toStringified', () => {
+    const typeInfo = new TypeInfo(testSchema);
+
+    expect(Object.prototype.toString.call(typeInfo)).to.equal(
+      '[object TypeInfo]',
+    );
+  });
+
   it('allow all methods to be called before entering any node', () => {
     const typeInfo = new TypeInfo(testSchema);
 

src/validation/ValidationContext.ts

@@ -131,6 +131,10 @@ export class ASTValidationContext {
     }
     return fragments;
   }
+
+  get [Symbol.toStringTag]() {
+    return 'ASTValidationContext';
+  }
 }
 
 export type ASTValidationRule = (context: ASTValidationContext) => ASTVisitor;
@@ -150,6 +154,10 @@ export class SDLValidationContext extends ASTValidationContext {
   getSchema(): Maybe<GraphQLSchema> {
     return this._schema;
   }
+
+  get [Symbol.toStringTag]() {
+    return 'SDLValidationContext';
+  }
 }
 
 export type SDLValidationRule = (context: SDLValidationContext) => ASTVisitor;
@@ -253,6 +261,10 @@ export class ValidationContext extends ASTValidationContext {
   getEnumValue(): Maybe<GraphQLEnumValue> {
     return this._typeInfo.getEnumValue();
   }
+
+  get [Symbol.toStringTag]() {
+    return 'ValidationContext';
+  }
 }
 
 export type ValidationRule = (context: ValidationContext) => ASTVisitor;

src/validation/__tests__/ValidationContext-test.ts

@@ -0,0 +1,40 @@
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import { identityFunc } from '../../jsutils/identityFunc';
+
+import { parse } from '../../language/parser';
+
+import { GraphQLSchema } from '../../type/schema';
+
+import { TypeInfo } from '../../utilities/TypeInfo';
+
+import {
+  ASTValidationContext,
+  SDLValidationContext,
+  ValidationContext,
+} from '../ValidationContext';
+
+describe('ValidationContext', () => {
+  it('can be Object.toStringified', () => {
+    const schema = new GraphQLSchema({});
+    const typeInfo = new TypeInfo(schema);
+    const ast = parse('{ foo }');
+    const onError = identityFunc;
+
+    const astContext = new ASTValidationContext(ast, onError);
+    expect(Object.prototype.toString.call(astContext)).to.equal(
+      '[object ASTValidationContext]',
+    );
+
+    const sdlContext = new SDLValidationContext(ast, schema, onError);
+    expect(Object.prototype.toString.call(sdlContext)).to.equal(
+      '[object SDLValidationContext]',
+    );
+
+    const context = new ValidationContext(schema, ast, typeInfo, onError);
+    expect(Object.prototype.toString.call(context)).to.equal(
+      '[object ValidationContext]',
+    );
+  });
+});