fix(eslint-plugin): [strict-boolean-expression] support falsy and truthy literals simultaneously

packages/eslint-plugin/src/rules/strict-boolean-expressions.ts

@@ -835,10 +835,12 @@ export default util.createRule<Options, MessageId>({
       );
 
       if (strings.length) {
-        if (strings.some(type => type.isStringLiteral() && type.value !== '')) {
-          variantTypes.add('truthy string');
-        } else {
+        if (
+          strings.some(type => !type.isStringLiteral() || type.value === '')
+        ) {
           variantTypes.add('string');
+        } else {
+          variantTypes.add('truthy string');
         }
       }
 
@@ -848,11 +850,12 @@ export default util.createRule<Options, MessageId>({
           ts.TypeFlags.NumberLike | ts.TypeFlags.BigIntLike,
         ),
       );
+
       if (numbers.length) {
-        if (numbers.some(type => type.isNumberLiteral() && type.value !== 0)) {
-          variantTypes.add('truthy number');
-        } else {
+        if (numbers.some(type => !type.isNumberLiteral() || type.value === 0)) {
           variantTypes.add('number');
+        } else {
+          variantTypes.add('truthy number');
         }
       }
 

packages/eslint-plugin/tests/rules/strict-boolean-expressions.test.ts

@@ -894,6 +894,7 @@ if (y) {
         declare const x: string | null; if (x) {}
         (x?: string) => !x;
         <T extends string | null | undefined>(x: T) => x ? 1 : 0;
+        function foo(x: '' | 'bar' | null) { if(!x) {} }
       `,
       errors: [
         {
@@ -956,6 +957,28 @@ if (y) {
             },
           ],
         },
+        {
+          messageId: 'conditionErrorNullableString',
+          line: 5,
+          column: 50,
+          suggestions: [
+            {
+              messageId: 'conditionFixCompareNullish',
+              output:
+                "        function foo(x: '' | 'bar' | null) { if(x == null) {} }",
+            },
+            {
+              messageId: 'conditionFixDefaultEmptyString',
+              output:
+                "        function foo(x: '' | 'bar' | null) { if(!(x ?? \"\")) {} }",
+            },
+            {
+              messageId: 'conditionFixCastBoolean',
+              output:
+                "        function foo(x: '' | 'bar' | null) { if(!Boolean(x)) {} }",
+            },
+          ],
+        },
       ],
     }),
 
@@ -965,6 +988,7 @@ if (y) {
         declare const x: number | null; if (x) {}
         (x?: number) => !x;
         <T extends number | null | undefined>(x: T) => x ? 1 : 0;
+        function foo(x: 0 | 1 | null) { if(!x) {} }
       `,
       errors: [
         {
@@ -1027,6 +1051,28 @@ if (y) {
             },
           ],
         },
+        {
+          messageId: 'conditionErrorNullableNumber',
+          line: 5,
+          column: 45,
+          suggestions: [
+            {
+              messageId: 'conditionFixCompareNullish',
+              output:
+                '        function foo(x: 0 | 1 | null) { if(x == null) {} }',
+            },
+            {
+              messageId: 'conditionFixDefaultZero',
+              output:
+                '        function foo(x: 0 | 1 | null) { if(!(x ?? 0)) {} }',
+            },
+            {
+              messageId: 'conditionFixCastBoolean',
+              output:
+                '        function foo(x: 0 | 1 | null) { if(!Boolean(x)) {} }',
+            },
+          ],
+        },
       ],
     }),