fix(eslint-plugin): [prefer-optional-chain] only look at left operand for requireNullish

packages/eslint-plugin/src/rules/prefer-optional-chain-utils/gatherLogicalOperands.ts

@@ -61,14 +61,15 @@ type Operand = ValidOperand | InvalidOperand;
 const NULLISH_FLAGS = ts.TypeFlags.Null | ts.TypeFlags.Undefined;
 function isValidFalseBooleanCheckType(
   node: TSESTree.Node,
-  operator: TSESTree.LogicalExpression['operator'],
+  operatorNode: TSESTree.LogicalExpression,
   checkType: 'true' | 'false',
   parserServices: ParserServicesWithTypeInformation,
   options: PreferOptionalChainOptions,
 ): boolean {
   const type = parserServices.getTypeAtLocation(node);
   const types = unionTypeParts(type);
 
+  const { operator } = operatorNode;
   const disallowFalseyLiteral =
     (operator === '||' && checkType === 'false') ||
     (operator === '&&' && checkType === 'true');
@@ -95,7 +96,10 @@ function isValidFalseBooleanCheckType(
   }
 
   if (options.requireNullish === true) {
-    return types.some(t => isTypeFlagSet(t, NULLISH_FLAGS));
+    return (
+      operatorNode.right === node ||
+      types.some(t => isTypeFlagSet(t, NULLISH_FLAGS))
+    );
   }
 
   let allowedFlags = NULLISH_FLAGS | ts.TypeFlags.Object;
@@ -258,7 +262,7 @@ export function gatherLogicalOperands(
           operand.operator === '!' &&
           isValidFalseBooleanCheckType(
             operand.argument,
-            node.operator,
+            node,
             'false',
             parserServices,
             options,
@@ -285,7 +289,7 @@ export function gatherLogicalOperands(
         if (
           isValidFalseBooleanCheckType(
             operand,
-            node.operator,
+            node,
             'true',
             parserServices,
             options,

packages/eslint-plugin/tests/rules/prefer-optional-chain/prefer-optional-chain.test.ts

@@ -786,22 +786,21 @@ describe('hand-crafted cases', () => {
           declare const x: string;
           x && x.length;
         `,
-        options: [
-          {
-            requireNullish: true,
-          },
-        ],
+        options: [{ requireNullish: true }],
       },
       {
         code: `
           declare const x: string | number | boolean | object;
           x && x.toString();
         `,
-        options: [
-          {
-            requireNullish: true,
-          },
-        ],
+        options: [{ requireNullish: true }],
+      },
+      {
+        code: `
+          declare const foo: { bar: string };
+          foo && foo.bar && foo.bar.toString();
+        `,
+        options: [{ requireNullish: true }],
       },
       {
         code: `
@@ -1866,6 +1865,16 @@ describe('hand-crafted cases', () => {
         ],
       },
 
+      // requireNullish
+      {
+        code: `
+          declare const thing1: string | null;
+          thing1 && thing1.toString();
+        `,
+        options: [{ requireNullish: true }],
+        errors: [{ messageId: `preferOptionalChain` }],
+      },
+
       // allowPotentiallyUnsafeFixesThatModifyTheReturnTypeIKnowWhatImDoing
       {
         code: `