feat(eslint-plugin): [no-unnecessary-condition][strict-boolean-expres…

…sions] add option to make the rules error on files without `strictNullChecks` turned on (#2345)

packages/eslint-plugin/docs/rules/no-unnecessary-condition.md

@@ -62,18 +62,40 @@ function bar(arg?: string | null) {
 
 ## Options
 
-Accepts an object with the following options:
+```ts
+type Options = {
+  // if true, the rule will ignore constant loop conditions
+  allowConstantLoopConditions?: boolean;
+  // if true, the rule will not error when running with a tsconfig that has strictNullChecks turned **off**
+  allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing?: boolean;
+};
+
+const defaultOptions: Options = {
+  allowConstantLoopConditions: false,
+  allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: false,
+};
+```
 
-- `allowConstantLoopConditions` (default `false`) - allows constant expressions in loops.
+### `allowConstantLoopConditions`
 
-Example of correct code for when `allowConstantLoopConditions` is `true`:
+Example of correct code for `{ allowConstantLoopConditions: true }`:
 
 ```ts
 while (true) {}
 for (; true; ) {}
 do {} while (true);
 ```
 
+### `allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing`
+
+If this is set to `false`, then the rule will error on every file whose `tsconfig.json` does _not_ have the `strictNullChecks` compiler option (or `strict`) set to `true`.
+
+Without `strictNullChecks`, TypeScript essentially erases `undefined` and `null` from the types. This means when this rule inspects the types from a variable, **it will not be able to tell that the variable might be `null` or `undefined`**, which essentially makes this rule useless.
+
+You should be using `strictNullChecks` to ensure complete type-safety in your codebase.
+
+If for some reason you cannot turn on `strictNullChecks`, but still want to use this rule - you can use this option to allow it - but know that the behavior of this rule is _undefined_ with the compiler option turned off. We will not accept bug reports if you are using this option.
+
 ## When Not To Use It
 
 The main downside to using this rule is the need for type information.

packages/eslint-plugin/docs/rules/strict-boolean-expressions.md

@@ -79,41 +79,81 @@ const foo = (arg: any) => (Boolean(arg) ? 1 : 0);
 
 ## Options
 
-Options may be provided as an object with:
-
-- `allowString` (`true` by default) -
-  Allows `string` in a boolean context.
-  This is safe because strings have only one falsy value (`""`).
-  Set this to `false` if you prefer the explicit `str != ""` or `str.length > 0` style.
-
-- `allowNumber` (`true` by default) -
-  Allows `number` in a boolean context.
-  This is safe because numbers have only two falsy values (`0` and `NaN`).
-  Set this to `false` if you prefer the explicit `num != 0` and `!Number.isNaN(num)` style.
-
-- `allowNullableObject` (`true` by default) -
-  Allows `object | function | symbol | null | undefined` in a boolean context.
-  This is safe because objects, functions and symbols don't have falsy values.
-  Set this to `false` if you prefer the explicit `obj != null` style.
-
-- `allowNullableBoolean` (`false` by default) -
-  Allows `boolean | null | undefined` in a boolean context.
-  This is unsafe because nullable booleans can be either `false` or nullish.
-  Set this to `false` if you want to enforce explicit `bool ?? false` or `bool ?? true` style.
-  Set this to `true` if you don't mind implicitly treating false the same as a nullish value.
-
-- `allowNullableString` (`false` by default) -
-  Allows `string | null | undefined` in a boolean context.
-  This is unsafe because nullable strings can be either an empty string or nullish.
-  Set this to `true` if you don't mind implicitly treating an empty string the same as a nullish value.
-
-- `allowNullableNumber` (`false` by default) -
-  Allows `number | null | undefined` in a boolean context.
-  This is unsafe because nullable numbers can be either a falsy number or nullish.
-  Set this to `true` if you don't mind implicitly treating zero or NaN the same as a nullish value.
-
-- `allowAny` (`false` by default) -
-  Allows `any` in a boolean context.
+```ts
+type Options = {
+  allowString?: boolean;
+  allowNumber?: boolean;
+  allowNullableObject?: boolean;
+  allowNullableBoolean?: boolean;
+  allowNullableString?: boolean;
+  allowNullableNumber?: boolean;
+  allowAny?: boolean;
+};
+
+const defaultOptions: Options = {
+  allowString: true,
+  allowNumber: true,
+  allowNullableObject: true,
+  allowNullableBoolean: false,
+  allowNullableString: false,
+  allowNullableNumber: false,
+  allowAny: false,
+  allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: false,
+};
+```
+
+### `allowString`
+
+Allows `string` in a boolean context.
+This is safe because strings have only one falsy value (`""`).
+Set this to `false` if you prefer the explicit `str != ""` or `str.length > 0` style.
+
+### `allowNumber`
+
+Allows `number` in a boolean context.
+This is safe because numbers have only two falsy values (`0` and `NaN`).
+Set this to `false` if you prefer the explicit `num != 0` and `!Number.isNaN(num)` style.
+
+### `allowNullableObject`
+
+Allows `object | function | symbol | null | undefined` in a boolean context.
+This is safe because objects, functions and symbols don't have falsy values.
+Set this to `false` if you prefer the explicit `obj != null` style.
+
+### `allowNullableBoolean`
+
+Allows `boolean | null | undefined` in a boolean context.
+This is unsafe because nullable booleans can be either `false` or nullish.
+Set this to `false` if you want to enforce explicit `bool ?? false` or `bool ?? true` style.
+Set this to `true` if you don't mind implicitly treating false the same as a nullish value.
+
+### `allowNullableString`
+
+Allows `string | null | undefined` in a boolean context.
+This is unsafe because nullable strings can be either an empty string or nullish.
+Set this to `true` if you don't mind implicitly treating an empty string the same as a nullish value.
+
+### `allowNullableNumber`
+
+Allows `number | null | undefined` in a boolean context.
+This is unsafe because nullable numbers can be either a falsy number or nullish.
+Set this to `true` if you don't mind implicitly treating zero or NaN the same as a nullish value.
+
+### `allowAny`
+
+Allows `any` in a boolean context.
+This is unsafe for obvious reasons.
+Set this to `true` at your own risk.
+
+### `allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing`
+
+If this is set to `false`, then the rule will error on every file whose `tsconfig.json` does _not_ have the `strictNullChecks` compiler option (or `strict`) set to `true`.
+
+Without `strictNullChecks`, TypeScript essentially erases `undefined` and `null` from the types. This means when this rule inspects the types from a variable, **it will not be able to tell that the variable might be `null` or `undefined`**, which essentially makes this rule a lot less useful.
+
+You should be using `strictNullChecks` to ensure complete type-safety in your codebase.
+
+If for some reason you cannot turn on `strictNullChecks`, but still want to use this rule - you can use this option to allow it - but know that the behavior of this rule is _undefined_ with the compiler option turned off. We will not accept bug reports if you are using this option.
 
 ## Related To
 

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

@@ -65,6 +65,7 @@ const isLiteral = (type: ts.Type): boolean =>
 export type Options = [
   {
     allowConstantLoopConditions?: boolean;
+    allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing?: boolean;
   },
 ];
 
@@ -78,7 +79,9 @@ export type MessageId =
   | 'literalBooleanExpression'
   | 'noOverlapBooleanExpression'
   | 'never'
-  | 'neverOptionalChain';
+  | 'neverOptionalChain'
+  | 'noStrictNullCheck';
+
 export default createRule<Options, MessageId>({
   name: 'no-unnecessary-condition',
   meta: {
@@ -97,6 +100,9 @@ export default createRule<Options, MessageId>({
           allowConstantLoopConditions: {
             type: 'boolean',
           },
+          allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: {
+            type: 'boolean',
+          },
         },
         additionalProperties: false,
       },
@@ -119,18 +125,46 @@ export default createRule<Options, MessageId>({
         'Unnecessary conditional, the types have no overlap',
       never: 'Unnecessary conditional, value is `never`',
       neverOptionalChain: 'Unnecessary optional chain on a non-nullish value',
+      noStrictNullCheck:
+        'This rule requires the `strictNullChecks` compiler option to be turned on to function correctly.',
     },
   },
   defaultOptions: [
     {
       allowConstantLoopConditions: false,
+      allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: false,
     },
   ],
-  create(context, [{ allowConstantLoopConditions }]) {
+  create(
+    context,
+    [
+      {
+        allowConstantLoopConditions,
+        allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing,
+      },
+    ],
+  ) {
     const service = getParserServices(context);
     const checker = service.program.getTypeChecker();
     const sourceCode = context.getSourceCode();
     const compilerOptions = service.program.getCompilerOptions();
+    const isStrictNullChecks = isStrictCompilerOptionEnabled(
+      compilerOptions,
+      'strictNullChecks',
+    );
+
+    if (
+      !isStrictNullChecks &&
+      allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing !== true
+    ) {
+      context.report({
+        loc: {
+          start: { line: 0, column: 0 },
+          end: { line: 0, column: 0 },
+        },
+        messageId: 'noStrictNullCheck',
+      });
+    }
 
     function getNodeType(node: TSESTree.Expression): ts.Type {
       const tsNode = service.esTreeNodeToTSNodeMap.get(node);
@@ -285,7 +319,7 @@ export default createRule<Options, MessageId>({
         return;
       }
       // Workaround for https://github.com/microsoft/TypeScript/issues/37160
-      if (isStrictCompilerOptionEnabled(compilerOptions, 'strictNullChecks')) {
+      if (isStrictNullChecks) {
         const UNDEFINED = ts.TypeFlags.Undefined;
         const NULL = ts.TypeFlags.Null;
         const isComparable = (type: ts.Type, flag: ts.TypeFlags): boolean => {

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

@@ -15,6 +15,7 @@ export type Options = [
     allowNullableString?: boolean;
     allowNullableNumber?: boolean;
     allowAny?: boolean;
+    allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing?: boolean;
   },
 ];
 
@@ -28,7 +29,8 @@ export type MessageId =
   | 'conditionErrorNumber'
   | 'conditionErrorNullableNumber'
   | 'conditionErrorObject'
-  | 'conditionErrorNullableObject';
+  | 'conditionErrorNullableObject'
+  | 'noStrictNullCheck';
 
 export default util.createRule<Options, MessageId>({
   name: 'strict-boolean-expressions',
@@ -51,6 +53,9 @@ export default util.createRule<Options, MessageId>({
           allowNullableString: { type: 'boolean' },
           allowNullableNumber: { type: 'boolean' },
           allowAny: { type: 'boolean' },
+          allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: {
+            type: 'boolean',
+          },
         },
         additionalProperties: false,
       },
@@ -86,18 +91,43 @@ export default util.createRule<Options, MessageId>({
       conditionErrorNullableObject:
         'Unexpected nullable object value in conditional. ' +
         'An explicit null check is required.',
+      noStrictNullCheck:
+        'This rule requires the `strictNullChecks` compiler option to be turned on to function correctly.',
     },
   },
   defaultOptions: [
     {
       allowString: true,
       allowNumber: true,
       allowNullableObject: true,
+      allowNullableBoolean: false,
+      allowNullableString: false,
+      allowNullableNumber: false,
+      allowAny: false,
+      allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: false,
     },
   ],
   create(context, [options]) {
     const service = util.getParserServices(context);
     const checker = service.program.getTypeChecker();
+    const compilerOptions = service.program.getCompilerOptions();
+    const isStrictNullChecks = tsutils.isStrictCompilerOptionEnabled(
+      compilerOptions,
+      'strictNullChecks',
+    );
+
+    if (
+      !isStrictNullChecks &&
+      options.allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing !== true
+    ) {
+      context.report({
+        loc: {
+          start: { line: 0, column: 0 },
+          end: { line: 0, column: 0 },
+        },
+        messageId: 'noStrictNullCheck',
+      });
+    }
 
     const checkedNodes = new Set<TSESTree.Node>();
 

packages/eslint-plugin/tests/fixtures/unstrict/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "jsx": "preserve",
+    "target": "es5",
+    "module": "commonjs",
+    "strict": false,
+    "esModuleInterop": true,
+    "lib": ["es2015", "es2017", "esnext"],
+    "experimentalDecorators": true
+  },
+  "include": [
+    "file.ts",
+    "react.tsx"
+  ]
+}

packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts

@@ -2,6 +2,7 @@ import {
   TestCaseError,
   InvalidTestCase,
 } from '@typescript-eslint/experimental-utils/dist/ts-eslint';
+import * as path from 'path';
 import rule, {
   Options,
   MessageId,
@@ -490,6 +491,22 @@ declare const unknownTyped: unknown;
 if (!(booleanTyped || unknownTyped)) {
 }
     `,
+    {
+      code: `
+declare const x: string[] | null;
+// eslint-disable-next-line
+if (x) {
+}
+      `,
+      options: [
+        {
+          allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: true,
+        },
+      ],
+      parserOptions: {
+        tsconfigRootDir: path.join(rootPath, 'unstrict'),
+      },
+    },
   ],
   invalid: [
     // Ensure that it's checking in all the right places
@@ -1461,5 +1478,27 @@ if (!speech) {
       `,
       errors: [ruleError(7, 6, 'never')],
     },
+    {
+      code: `
+declare const x: string[] | null;
+if (x) {
+}
+      `,
+      errors: [
+        {
+          messageId: 'noStrictNullCheck',
+          line: 0,
+          column: 1,
+        },
+        {
+          messageId: 'alwaysTruthy',
+          line: 3,
+          column: 5,
+        },
+      ],
+      parserOptions: {
+        tsconfigRootDir: path.join(rootPath, 'unstrict'),
+      },
+    },
   ],
 });