strict-type-predicates: warn if strictNullChecks is not enabled

src/language/utils.ts

@@ -425,3 +425,8 @@ export function getEqualsKind(node: ts.BinaryOperatorToken): EqualsKind | undefi
             return undefined;
     }
 }
+
+export function isStrictNullChecksEnabled(options: ts.CompilerOptions): boolean {
+    return options.strictNullChecks === true ||
+        (options.strict === true && options.strictNullChecks !== false);
+}

src/rules/strictBooleanExpressionsRule.ts

@@ -74,7 +74,7 @@ export class Rule extends Lint.Rules.TypedRule {
     };
 
     public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
-        const options = parseOptions(this.ruleArguments, program.getCompilerOptions().strictNullChecks === true);
+        const options = parseOptions(this.ruleArguments, Lint.isStrictNullChecksEnabled(program.getCompilerOptions()));
         return this.applyWithFunction(sourceFile, (ctx: Lint.WalkContext<Options>) => walk(ctx, program.getTypeChecker()), options);
     }
 }

src/rules/strictTypePredicatesRule.ts

@@ -18,6 +18,7 @@
 import { isBinaryExpression, isUnionType } from "tsutils";
 
 import * as ts from "typescript";
+import { showWarningOnce } from "../error";
 import * as Lint from "../index";
 
 // tslint:disable:no-bitwise
@@ -31,7 +32,9 @@ export class Rule extends Lint.Rules.TypedRule {
             Works for 'typeof' comparisons to constants (e.g. 'typeof foo === "string"'), and equality comparison to 'null'/'undefined'.
             (TypeScript won't let you compare '1 === 2', but it has an exception for '1 === undefined'.)
             Does not yet work for 'instanceof'.
-            Does *not* warn for 'if (x.y)' where 'x.y' is always truthy. For that, see strict-boolean-expressions.`,
+            Does *not* warn for 'if (x.y)' where 'x.y' is always truthy. For that, see strict-boolean-expressions.
+
+            This rule requires \`strictNullChecks\` to work properly.`,
         optionsDescription: "Not configurable.",
         options: null,
         optionExamples: [true],
@@ -52,6 +55,10 @@ export class Rule extends Lint.Rules.TypedRule {
     }
 
     public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+        if (!Lint.isStrictNullChecksEnabled(program.getCompilerOptions())) {
+            showWarningOnce("strict-type-predicates does not work without strictNullChecks");
+            return [];
+        }
         return this.applyWithFunction(sourceFile, (ctx) => walk(ctx, program.getTypeChecker()));
     }
 }

test/rules/strict-boolean-expressions/no-null-checks-allow-null-union/tsconfig.json

@@ -1,5 +1,6 @@
 {
     "compilerOptions": {
-        "module": "commonjs"
+        "strict": true,
+        "strictNullChecks": false
     }
 }

test/rules/strict-boolean-expressions/no-null-checks-allow-number-string/tsconfig.json

@@ -1,5 +1,5 @@
 {
     "compilerOptions": {
-        "module": "commonjs"
+        "strictNullChecks": false
     }
 }

test/rules/strict-type-predicates/no-strict-null-checks/test.ts.lint

@@ -0,0 +1,156 @@
+declare function get<T>(): T;
+
+// typeof undefined
+{
+    typeof get<boolean>() === "undefined";
+
+    typeof get<void>() === "undefined";
+
+    typeof get<boolean | undefined>() === "undefined";
+
+    declare const c: any;
+    typeof get<any>() === "undefined";
+
+    // 'undefined' is not assignable to '{}'
+    typeof get<{}>() === "undefined";
+}
+
+// typeof boolean
+{
+    declare const a: boolean;
+    typeof get<boolean>() === "boolean";
+
+    typeof get<Boolean>() === "boolean";
+
+    typeof get<boolean | undefined>() === "boolean";
+
+    typeof get<{}>() === "boolean";
+}
+
+// typeof number
+{
+    enum E {}
+
+    typeof get<E>() === "number";
+
+    typeof get<Number>() === "number";
+}
+
+// typeof string
+{
+    typeof get<"abc" | "def">() === "string";
+
+    typeof get<String>() === "string";
+
+    typeof get<"abc" | undefined>() === "string";
+}
+
+// typeof symbol
+{
+    typeof get<symbol>() === "symbol";
+
+    typeof get<string>() === "symbol";
+
+    typeof get<symbol | string>() === "symbol";
+}
+
+// typeof function
+{
+    typeof get<() => void>() === "function";
+
+    typeof get<Function>() === "function";
+
+
+    typeof get<number>() === "function";
+
+    typeof get<number | (() => void)>() === "function";
+
+    class X {}
+    typeof X === "function";
+    typeof X === "object";
+
+    // Works with union
+    class Foo { }
+    typeof get<typeof Foo | object> === "function";
+}
+
+// typeof object
+{
+    typeof get<boolean | number | string | symbol | (() => void) | Function>() === "object";
+
+    typeof get<{}> === "object";
+}
+
+// === null / undefined
+{
+    get<number | undefined>() === null;
+
+    get<number | null>() === null;
+
+    get<number | null>() === undefined;
+
+    get<number | undefined>() === undefined;
+
+    // 'null' and 'undefined' are not assignable to '{}'
+
+    get<{}>() === null;
+
+    get<{}>() === undefined;
+
+    get<string | undefined>() == null;
+
+    get<string | null>() == undefined;
+
+    get<string | null>() == null;
+
+    get<string | undefined>() == undefined;
+
+    get<string | undefined>() != null;
+
+    get<{}>() == null;
+
+    get<string | null | undefined>() == null;
+    get<string | null | undefined>() != undefined;
+
+    get<null|undefined>() == null;
+    get<null|undefined>() != undefined;
+}
+
+// negation
+{
+    get<number | undefined>() !== null;
+
+    get<number | null>() !== null;
+
+    get<number | null>() !== undefined;
+
+    get<number | undefined>() !== undefined;
+
+    typeof get<string>() !== "string";
+}
+
+// reverse left/right
+{
+    "string" === typeof get<number>();
+
+    undefined === get<void>();
+}
+
+// type parameters
+{
+    function f<T>(t: T) {
+        typeof t === "boolean";
+    }
+
+    // TODO: Would be nice to catch this.
+    function g<T extends string>(t: T) {
+        typeof t === "boolean";
+    }
+}
+
+// Detects bad typeof
+{
+    typeof get<boolean>() === true;
+
+    typeof get<any>() === "orbject";
+}

test/rules/strict-type-predicates/no-strict-null-checks/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        // strictNullChecks not enabled
+    }
+}

test/rules/strict-type-predicates/strict-null-checks/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "strict-type-predicates": true
+  }
+}