fix(eslint-plugin): [no-throw-literal] false positive with logical expressions (typescript-eslint#2645)

jsone-studios · web-flow · commit 57aa6c764232 · 2020-10-11T16:54:12.000-07:00
diff --git a/packages/eslint-plugin/src/rules/no-throw-literal.ts b/packages/eslint-plugin/src/rules/no-throw-literal.ts
@@ -61,40 +61,6 @@ export default util.createRule({
       return false;
     }
 
-    function tryGetThrowArgumentType(node: TSESTree.Node): ts.Type | null {
-      switch (node.type) {
-        case AST_NODE_TYPES.Identifier:
-        case AST_NODE_TYPES.CallExpression:
-        case AST_NODE_TYPES.NewExpression:
-        case AST_NODE_TYPES.MemberExpression:
-        case AST_NODE_TYPES.TSAsExpression: {
-          const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
-          return checker.getTypeAtLocation(tsNode);
-        }
-
-        case AST_NODE_TYPES.AssignmentExpression:
-          return tryGetThrowArgumentType(node.right);
-
-        case AST_NODE_TYPES.SequenceExpression:
-          return tryGetThrowArgumentType(
-            node.expressions[node.expressions.length - 1],
-          );
-
-        case AST_NODE_TYPES.LogicalExpression: {
-          const left = tryGetThrowArgumentType(node.left);
-          return left ?? tryGetThrowArgumentType(node.right);
-        }
-
-        case AST_NODE_TYPES.ConditionalExpression: {
-          const consequent = tryGetThrowArgumentType(node.consequent);
-          return consequent ?? tryGetThrowArgumentType(node.alternate);
-        }
-
-        default:
-          return null;
-      }
-    }
-
     function checkThrowArgument(node: TSESTree.Node): void {
       if (
         node.type === AST_NODE_TYPES.AwaitExpression ||
@@ -103,20 +69,20 @@ export default util.createRule({
         return;
       }
 
-      const type = tryGetThrowArgumentType(node);
-      if (type) {
-        if (type.flags & ts.TypeFlags.Undefined) {
-          context.report({ node, messageId: 'undef' });
-          return;
-        }
+      const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
+      const type = checker.getTypeAtLocation(tsNode);
 
-        if (
-          util.isTypeAnyType(type) ||
-          util.isTypeUnknownType(type) ||
-          isErrorLike(type)
-        ) {
-          return;
-        }
+      if (type.flags & ts.TypeFlags.Undefined) {
+        context.report({ node, messageId: 'undef' });
+        return;
+      }
+
+      if (
+        util.isTypeAnyType(type) ||
+        util.isTypeUnknownType(type) ||
+        isErrorLike(type)
+      ) {
+        return;
       }
 
       context.report({ node, messageId: 'object' });
diff --git a/packages/eslint-plugin/tests/rules/no-throw-literal.test.ts b/packages/eslint-plugin/tests/rules/no-throw-literal.test.ts
@@ -61,14 +61,13 @@ throw new CustomError();
     `
 class CustomError1 extends Error {}
 class CustomError2 extends CustomError1 {}
-throw new CustomError();
+throw new CustomError2();
     `,
     'throw (foo = new Error());',
     'throw (1, 2, new Error());',
     "throw 'literal' && new Error();",
     "throw new Error() || 'literal';",
-    "throw foo ? new Error() : 'literal';",
-    "throw foo ? 'literal' : new Error();",
+    'throw foo ? new Error() : new Error();',
     `
 function* foo() {
   let index = 0;
@@ -112,6 +111,18 @@ declare const foo: Error | string;
 throw foo as Error;
     `,
     'throw new Error() as Error;',
+    `
+declare const nullishError: Error | undefined;
+throw nullishError ?? new Error();
+    `,
+    `
+declare const nullishError: Error | undefined;
+throw nullishError || new Error();
+    `,
+    `
+declare const nullishError: Error | undefined;
+throw nullishError ? nullishError : new Error();
+    `,
   ],
   invalid: [
     {
@@ -207,19 +218,31 @@ throw a + 'b';
     },
     {
       code: "throw 'literal' && 'not an Error';",
-      errors: [
-        {
-          messageId: 'object',
-        },
-      ],
+      errors: [{ messageId: 'object' }],
+    },
+    {
+      code: "throw 'literal' || new Error();",
+      errors: [{ messageId: 'object' }],
+    },
+    {
+      code: "throw new Error() && 'literal';",
+      errors: [{ messageId: 'object' }],
+    },
+    {
+      code: "throw 'literal' ?? new Error();",
+      errors: [{ messageId: 'object' }],
     },
     {
       code: "throw foo ? 'not an Error' : 'literal';",
-      errors: [
-        {
-          messageId: 'object',
-        },
-      ],
+      errors: [{ messageId: 'object' }],
+    },
+    {
+      code: "throw foo ? new Error() : 'literal';",
+      errors: [{ messageId: 'object' }],
+    },
+    {
+      code: "throw foo ? 'literal' : new Error();",
+      errors: [{ messageId: 'object' }],
     },
     {
       code: 'throw `${err}`;',
