fix(eslint-plugin): support BigInt in restrict-plus-operands rule

packages/eslint-plugin/docs/rules/restrict-plus-operands.md

@@ -4,12 +4,14 @@ Examples of **correct** code:
 
 ```ts
 var foo = parseInt('5.5', 10) + 10;
+var foo = 1n + 1n;
 ```
 
 Examples of **incorrect** code:
 
 ```ts
 var foo = '5.5' + 5;
+var foo = 1n + 1;
 ```
 
 ## Options

packages/eslint-plugin/src/rules/restrict-plus-operands.ts

@@ -24,6 +24,7 @@ export default util.createRule({
         "Operands of '+' operation must either be both strings or both numbers.",
       notStrings:
         "Operands of '+' operation must either be both strings or both numbers. Consider using a template literal.",
+      notBigInts: "Operands of '+' operation must be both bigints.",
     },
     schema: [],
   },
@@ -33,7 +34,7 @@ export default util.createRule({
 
     const typeChecker = service.program.getTypeChecker();
 
-    type BaseLiteral = 'string' | 'number' | 'invalid';
+    type BaseLiteral = 'string' | 'number' | 'bigint' | 'invalid';
 
     /**
      * Helper function to get base type of node
@@ -47,6 +48,10 @@ export default util.createRule({
       if (type.isStringLiteral()) {
         return 'string';
       }
+      // is BigIntLiteral
+      if (type.flags & ts.TypeFlags.BigIntLiteral) {
+        return 'bigint';
+      }
       if (type.isUnion()) {
         const types = type.types.map(getBaseTypeOfLiteralType);
 
@@ -87,6 +92,11 @@ export default util.createRule({
               node,
               messageId: 'notStrings',
             });
+          } else if (leftType === 'bigint' || rightType === 'bigint') {
+            context.report({
+              node,
+              messageId: 'notBigInts',
+            });
           } else {
             context.report({
               node,

packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts

@@ -22,6 +22,7 @@ ruleTester.run('restrict-plus-operands', rule, {
     `var foo = "5.5" + "10";`,
     `var foo = parseInt("5.5", 10) + 10;`,
     `var foo = parseFloat("5.5", 10) + 10;`,
+    `var foo = 1n + 1n;`,
     `
 function test () : number { return 2; }
 var foo = test("5.5", 10) + 10;
@@ -262,5 +263,25 @@ var foo = pair + pair;
         },
       ],
     },
+    {
+      code: `var foo = 1n + 1`,
+      errors: [
+        {
+          messageId: 'notBigInts',
+          line: 1,
+          column: 11,
+        },
+      ],
+    },
+    {
+      code: `var foo = 1 + 1n`,
+      errors: [
+        {
+          messageId: 'notBigInts',
+          line: 1,
+          column: 11,
+        },
+      ],
+    },
   ],
 });