chore: turn on prefer-nullish-coalescing locally (#1259)

.eslintrc.js

@@ -28,6 +28,7 @@ module.exports = {
     '@typescript-eslint/no-non-null-assertion': 'off',
     '@typescript-eslint/no-use-before-define': 'off',
     '@typescript-eslint/no-var-requires': 'off',
+    '@typescript-eslint/prefer-nullish-coalescing': 'error',
     '@typescript-eslint/prefer-optional-chain': 'error',
     '@typescript-eslint/unbound-method': 'off',
 

packages/eslint-plugin-tslint/src/rules/config.ts

@@ -47,8 +47,8 @@ const tslintConfig = memoize(
       return Configuration.loadConfigurationFromPath(lintFile);
     }
     return Configuration.parseConfigFile({
-      rules: tslintRules || {},
-      rulesDirectory: tslintRulesDirectory || [],
+      rules: tslintRules ?? {},
+      rulesDirectory: tslintRulesDirectory ?? [],
     });
   },
   (lintFile: string | undefined, tslintRules = {}, tslintRulesDirectory = []) =>

packages/eslint-plugin/src/rules/array-type.ts

@@ -127,7 +127,7 @@ export default util.createRule<Options, MessageIds>({
     const sourceCode = context.getSourceCode();
 
     const defaultOption = options.default;
-    const readonlyOption = options.readonly || defaultOption;
+    const readonlyOption = options.readonly ?? defaultOption;
 
     const isArraySimpleOption =
       defaultOption === 'array-simple' && readonlyOption === 'array-simple';

packages/eslint-plugin/src/rules/camelcase.ts

@@ -52,10 +52,11 @@ export default util.createRule<Options, MessageIds>({
 
     const genericType = options.genericType;
     const properties = options.properties;
-    const allow = (options.allow || []).map(entry => ({
-      name: entry,
-      regex: new RegExp(entry),
-    }));
+    const allow =
+      options.allow?.map(entry => ({
+        name: entry,
+        regex: new RegExp(entry),
+      })) ?? [];
 
     /**
      * Checks if a string contains an underscore and isn't all upper-case

packages/eslint-plugin/src/rules/consistent-type-definitions.ts

@@ -36,7 +36,7 @@ export default util.createRule({
             node: node.id,
             messageId: 'interfaceOverType',
             fix(fixer) {
-              const typeNode = node.typeParameters || node.id;
+              const typeNode = node.typeParameters ?? node.id;
               const fixes: TSESLint.RuleFix[] = [];
 
               const firstToken = sourceCode.getFirstToken(node);
@@ -70,7 +70,7 @@ export default util.createRule({
             node: node.id,
             messageId: 'typeOverInterface',
             fix(fixer) {
-              const typeNode = node.typeParameters || node.id;
+              const typeNode = node.typeParameters ?? node.id;
               const fixes: TSESLint.RuleFix[] = [];
 
               const firstToken = sourceCode.getFirstToken(node);

packages/eslint-plugin/src/rules/explicit-member-accessibility.ts

@@ -75,14 +75,14 @@ export default util.createRule<Options, MessageIds>({
   defaultOptions: [{ accessibility: 'explicit' }],
   create(context, [option]) {
     const sourceCode = context.getSourceCode();
-    const baseCheck: AccessibilityLevel = option.accessibility || 'explicit';
-    const overrides = option.overrides || {};
-    const ctorCheck = overrides.constructors || baseCheck;
-    const accessorCheck = overrides.accessors || baseCheck;
-    const methodCheck = overrides.methods || baseCheck;
-    const propCheck = overrides.properties || baseCheck;
-    const paramPropCheck = overrides.parameterProperties || baseCheck;
-    const ignoredMethodNames = new Set(option.ignoredMethodNames || []);
+    const baseCheck: AccessibilityLevel = option.accessibility ?? 'explicit';
+    const overrides = option.overrides ?? {};
+    const ctorCheck = overrides.constructors ?? baseCheck;
+    const accessorCheck = overrides.accessors ?? baseCheck;
+    const methodCheck = overrides.methods ?? baseCheck;
+    const propCheck = overrides.properties ?? baseCheck;
+    const paramPropCheck = overrides.parameterProperties ?? baseCheck;
+    const ignoredMethodNames = new Set(option.ignoredMethodNames ?? []);
     /**
      * Generates the report for rule violations
      */

packages/eslint-plugin/src/rules/func-call-spacing.ts

@@ -82,7 +82,7 @@ export default util.createRule<Options, MessageIds>({
 
       const closingParenToken = sourceCode.getLastToken(node)!;
       const lastCalleeTokenWithoutPossibleParens = sourceCode.getLastToken(
-        node.typeParameters || node.callee,
+        node.typeParameters ?? node.callee,
       )!;
       const openingParenToken = sourceCode.getFirstTokenBetween(
         lastCalleeTokenWithoutPossibleParens,

packages/eslint-plugin/src/rules/member-delimiter-style.ts

@@ -104,7 +104,7 @@ export default util.createRule<Options, MessageIds>({
 
     // use the base options as the defaults for the cases
     const baseOptions = options;
-    const overrides = baseOptions.overrides || {};
+    const overrides = baseOptions.overrides ?? {};
     const interfaceOptions: BaseOptions = util.deepMerge(
       baseOptions,
       overrides.interface,
@@ -227,7 +227,7 @@ export default util.createRule<Options, MessageIds>({
       const opts = isSingleLine ? typeOpts.singleline : typeOpts.multiline;
 
       members.forEach((member, index) => {
-        checkLastToken(member, opts || {}, index === members.length - 1);
+        checkLastToken(member, opts ?? {}, index === members.length - 1);
       });
     }
 

packages/eslint-plugin/src/rules/member-ordering.ts

@@ -388,28 +388,28 @@ export default util.createRule<Options, MessageIds>({
       ClassDeclaration(node): void {
         validateMembersOrder(
           node.body.body,
-          options.classes || options.default!,
+          options.classes ?? options.default!,
           true,
         );
       },
       ClassExpression(node): void {
         validateMembersOrder(
           node.body.body,
-          options.classExpressions || options.default!,
+          options.classExpressions ?? options.default!,
           true,
         );
       },
       TSInterfaceDeclaration(node): void {
         validateMembersOrder(
           node.body.body,
-          options.interfaces || options.default!,
+          options.interfaces ?? options.default!,
           false,
         );
       },
       TSTypeLiteral(node): void {
         validateMembersOrder(
           node.members,
-          options.typeLiterals || options.default!,
+          options.typeLiterals ?? options.default!,
           false,
         );
       },

packages/eslint-plugin/src/rules/no-unnecessary-qualifier.ts

@@ -40,7 +40,7 @@ export default util.createRule({
     }
 
     function symbolIsNamespaceInScope(symbol: ts.Symbol): boolean {
-      const symbolDeclarations = symbol.getDeclarations() || [];
+      const symbolDeclarations = symbol.getDeclarations() ?? [];
 
       if (
         symbolDeclarations.some(decl =>

packages/eslint-plugin/src/rules/no-unused-vars-experimental.ts

@@ -78,7 +78,7 @@ export default util.createRule<Options, MessageIds>({
           ? new RegExp(userOptions.ignoredNamesRegex)
           : null,
       ignoreArgsIfArgsAfterAreUsed:
-        userOptions.ignoreArgsIfArgsAfterAreUsed || false,
+        userOptions.ignoreArgsIfArgsAfterAreUsed ?? false,
     };
 
     function handleIdentifier(identifier: ts.Identifier): void {

packages/eslint-plugin/src/rules/space-before-function-paren.ts

@@ -108,14 +108,14 @@ export default util.createRule<Options, MessageIds>({
           node.async &&
           isOpeningParenToken(sourceCode.getFirstToken(node, { skip: 1 })!)
         ) {
-          return overrideConfig.asyncArrow || baseConfig;
+          return overrideConfig.asyncArrow ?? baseConfig;
         }
       } else if (isNamedFunction(node)) {
-        return overrideConfig.named || baseConfig;
+        return overrideConfig.named ?? baseConfig;
 
         // `generator-star-spacing` should warn anonymous generators. E.g. `function* () {}`
       } else if (!node.generator) {
-        return overrideConfig.anonymous || baseConfig;
+        return overrideConfig.anonymous ?? baseConfig;
       }
 
       return 'ignore';

packages/eslint-plugin/src/rules/type-annotation-spacing.ts

@@ -76,7 +76,7 @@ export default util.createRule<Options, MessageIds>({
     const punctuators = [':', '=>'];
     const sourceCode = context.getSourceCode();
 
-    const overrides = options!.overrides || { colon: {}, arrow: {} };
+    const overrides = options?.overrides ?? { colon: {}, arrow: {} };
 
     const colonOptions = Object.assign(
       {},

packages/eslint-plugin/src/rules/unified-signatures.ts

@@ -500,7 +500,7 @@ export default util.createRule({
       key?: string,
       containingNode?: ContainingNode,
     ): void {
-      key = key || getOverloadKey(signature);
+      key = key ?? getOverloadKey(signature);
       if (
         currentScope &&
         (containingNode || signature).parent === currentScope.parent

packages/eslint-plugin/src/util/types.ts

@@ -111,7 +111,7 @@ export function getConstrainedTypeAtLocation(
   const nodeType = checker.getTypeAtLocation(node);
   const constrained = checker.getBaseConstraintOfType(nodeType);
 
-  return constrained || nodeType;
+  return constrained ?? nodeType;
 }
 
 /**

packages/eslint-plugin/tests/rules/no-explicit-any.test.ts

@@ -1009,7 +1009,7 @@ const test = <T extends Partial<never>>() => {};
         suggestions: e.suggestions ?? suggestions(testCase.code),
       })),
     });
-    const options = testCase.options || [];
+    const options = testCase.options ?? [];
     const code = `// fixToUnknown: true\n${testCase.code}`;
     acc.push({
       code,

packages/parser/src/analyze-scope.ts

@@ -879,7 +879,7 @@ export function analyzeScope(
         parserOptions.ecmaFeatures.globalReturn) === true,
     impliedStrict: false,
     sourceType: parserOptions.sourceType,
-    ecmaVersion: parserOptions.ecmaVersion || 2018,
+    ecmaVersion: parserOptions.ecmaVersion ?? 2018,
     childVisitorKeys,
     fallback,
   };

packages/typescript-estree/src/convert.ts

@@ -111,7 +111,7 @@ export class Converter {
       this.allowPattern = allowPattern;
     }
 
-    const result = this.convertNode(node as TSNode, parent || node.parent);
+    const result = this.convertNode(node as TSNode, parent ?? node.parent);
 
     this.registerTSNodeInNodeMap(node, result);
 
@@ -1193,12 +1193,12 @@ export class Converter {
           if (node.dotDotDotToken) {
             result = this.createNode<TSESTree.RestElement>(node, {
               type: AST_NODE_TYPES.RestElement,
-              argument: this.convertChild(node.propertyName || node.name),
+              argument: this.convertChild(node.propertyName ?? node.name),
             });
           } else {
             result = this.createNode<TSESTree.Property>(node, {
               type: AST_NODE_TYPES.Property,
-              key: this.convertChild(node.propertyName || node.name),
+              key: this.convertChild(node.propertyName ?? node.name),
               value: this.convertChild(node.name),
               computed: Boolean(
                 node.propertyName &&
@@ -1387,7 +1387,7 @@ export class Converter {
         if (node.modifiers) {
           return this.createNode<TSESTree.TSParameterProperty>(node, {
             type: AST_NODE_TYPES.TSParameterProperty,
-            accessibility: getTSNodeAccessibility(node) || undefined,
+            accessibility: getTSNodeAccessibility(node) ?? undefined,
             readonly:
               hasModifier(SyntaxKind.ReadonlyKeyword, node) || undefined,
             static: hasModifier(SyntaxKind.StaticKeyword, node) || undefined,
@@ -1402,7 +1402,7 @@ export class Converter {
 
       case SyntaxKind.ClassDeclaration:
       case SyntaxKind.ClassExpression: {
-        const heritageClauses = node.heritageClauses || [];
+        const heritageClauses = node.heritageClauses ?? [];
         const classNodeType =
           node.kind === SyntaxKind.ClassDeclaration
             ? AST_NODE_TYPES.ClassDeclaration
@@ -1533,7 +1533,7 @@ export class Converter {
         return this.createNode<TSESTree.ImportSpecifier>(node, {
           type: AST_NODE_TYPES.ImportSpecifier,
           local: this.convertChild(node.name),
-          imported: this.convertChild(node.propertyName || node.name),
+          imported: this.convertChild(node.propertyName ?? node.name),
         });
 
       case SyntaxKind.ImportClause:
@@ -1563,7 +1563,7 @@ export class Converter {
       case SyntaxKind.ExportSpecifier:
         return this.createNode<TSESTree.ExportSpecifier>(node, {
           type: AST_NODE_TYPES.ExportSpecifier,
-          local: this.convertChild(node.propertyName || node.name),
+          local: this.convertChild(node.propertyName ?? node.name),
           exported: this.convertChild(node.name),
         });
 
@@ -1584,7 +1584,7 @@ export class Converter {
 
       case SyntaxKind.PrefixUnaryExpression:
       case SyntaxKind.PostfixUnaryExpression: {
-        const operator = (getTextForTokenKind(node.operator) || '') as any;
+        const operator = (getTextForTokenKind(node.operator) ?? '') as any;
         /**
          * ESTree uses UpdateExpression for ++/--
          */
@@ -2375,7 +2375,7 @@ export class Converter {
       }
 
       case SyntaxKind.InterfaceDeclaration: {
-        const interfaceHeritageClauses = node.heritageClauses || [];
+        const interfaceHeritageClauses = node.heritageClauses ?? [];
         const result = this.createNode<TSESTree.TSInterfaceDeclaration>(node, {
           type: AST_NODE_TYPES.TSInterfaceDeclaration,
           body: this.createNode<TSESTree.TSInterfaceBody>(node, {

packages/typescript-estree/src/create-program/createWatchProgram.ts

@@ -174,7 +174,7 @@ function getProgramsForProjects(
       log('Found existing program for file. %s', filePath);
 
       updatedProgram =
-        updatedProgram || existingWatch.getProgram().getProgram();
+        updatedProgram ?? existingWatch.getProgram().getProgram();
       // sets parent pointers in source files
       updatedProgram.getTypeChecker();
 

packages/typescript-estree/src/simple-traverse.ts

@@ -11,7 +11,7 @@ function getVisitorKeysForNode(
   node: TSESTree.Node,
 ): readonly string[] {
   const keys = allVisitorKeys[node.type];
-  return keys || [];
+  return keys ?? [];
 }
 
 interface SimpleTraverseOptions {

packages/typescript-estree/tests/ast-alignment/fixtures-to-test.ts

@@ -57,9 +57,9 @@ class FixturesTester {
       }
     }
 
-    const ignore = config.ignore || [];
-    const fileType = config.fileType || 'js';
-    const ignoreSourceType = config.ignoreSourceType || [];
+    const ignore = config.ignore ?? [];
+    const fileType = config.fileType ?? 'js';
+    const ignoreSourceType = config.ignoreSourceType ?? [];
     const jsx = isJSXFileType(fileType);
 
     /**