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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,19 @@ | ||
| --- | ||
| ruleName: strict-type-predicates | ||
| description: |- | ||
|
|
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| Warns for type predicates that are always true or always false. | ||
| Works for 'typeof' comparisons to constants (e.g. 'typeof foo === "string"'), and equality comparison to 'null'/'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. | ||
| optionsDescription: Not configurable. | ||
| options: null | ||
| optionExamples: | ||
| - 'true' | ||
| type: functionality | ||
| typescriptOnly: true | ||
| requiresTypeInfo: true | ||
| layout: rule | ||
| title: 'Rule: strict-type-predicates' | ||
| optionsJSON: 'null' | ||
| --- |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,210 @@ | ||
| /** | ||
| * @license | ||
| * Copyright 2016 Palantir Technologies, Inc. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
|
|
||
| import * as ts from "typescript"; | ||
| import * as Lint from "../index"; | ||
|
|
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| // tslint:disable:no-bitwise | ||
|
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| export class Rule extends Lint.Rules.TypedRule { | ||
| /* tslint:disable:object-literal-sort-keys */ | ||
| public static metadata: Lint.IRuleMetadata = { | ||
| ruleName: "strict-type-predicates", | ||
| description: Lint.Utils.dedent` | ||
| Warns for type predicates that are always true or always false. | ||
| 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.`, | ||
| optionsDescription: "Not configurable.", | ||
| options: null, | ||
| optionExamples: ["true"], | ||
| type: "functionality", | ||
| typescriptOnly: true, | ||
| requiresTypeInfo: true, | ||
| }; | ||
| /* tslint:enable:object-literal-sort-keys */ | ||
|
|
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| public static FAILURE_STRING(value: boolean): string { | ||
| return `Expression is always ${value}.`; | ||
| } | ||
|
|
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| public applyWithProgram(srcFile: ts.SourceFile, langSvc: ts.LanguageService): Lint.RuleFailure[] { | ||
| return this.applyWithWalker(new Walker(srcFile, this.getOptions(), langSvc.getProgram())); | ||
| } | ||
| } | ||
|
|
||
| class Walker extends Lint.ProgramAwareRuleWalker { | ||
| public visitBinaryExpression(node: ts.BinaryExpression) { | ||
| const equals = getEquals(node.operatorToken.kind); | ||
| if (equals) { | ||
| this.checkEquals(node, equals); | ||
| } | ||
| super.visitBinaryExpression(node); | ||
| } | ||
|
|
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| private checkEquals(node: ts.BinaryExpression, { isStrict, isPositive }: Equals) { | ||
| const exprPred = getTypePredicate(node, isStrict); | ||
| if (!exprPred) { | ||
| return; | ||
| } | ||
|
|
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| const { expression, predicate, isNullOrUndefined } = exprPred; | ||
| const checker = this.getTypeChecker(); | ||
| const exprType = checker.getTypeAtLocation(expression); | ||
| // TODO: could use checker.getBaseConstraintOfType to help with type parameters, but it's not publicly exposed. | ||
| if (Lint.isTypeFlagSet(exprType, ts.TypeFlags.Any | ts.TypeFlags.TypeParameter)) { | ||
| return; | ||
| } | ||
|
|
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| const value = getConstantBoolean(exprType, predicate); | ||
| // 'null'/'undefined' are the only two values *not* assignable to '{}'. | ||
| if (value !== undefined && (isNullOrUndefined || !isEmptyType(checker, exprType))) { | ||
| this.addFailureAtNode(node, Rule.FAILURE_STRING(value === isPositive)); | ||
| } | ||
| } | ||
| } | ||
|
|
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| /** Detects a type predicate given `left === right`. */ | ||
| function getTypePredicate(node: ts.BinaryExpression, isStrictEquals: boolean): TypePredicate | undefined { | ||
| const { left, right } = node; | ||
| return getTypePredicateOneWay(left, right, isStrictEquals) || getTypePredicateOneWay(right, left, isStrictEquals); | ||
| } | ||
|
|
||
| /** Only gets the type predicate if the expression is on the left. */ | ||
| function getTypePredicateOneWay(left: ts.Expression, right: ts.Expression, isStrictEquals: boolean): TypePredicate | undefined { | ||
| switch (right.kind) { | ||
| case ts.SyntaxKind.StringLiteral: | ||
| if (left.kind !== ts.SyntaxKind.TypeOfExpression) { | ||
| return undefined; | ||
| } | ||
| const expression = (left as ts.TypeOfExpression).expression; | ||
| const kind = (right as ts.StringLiteral).text; | ||
| return { expression, predicate: getTypePredicateForKind(kind), isNullOrUndefined: kind === "undefined" }; | ||
|
|
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| case ts.SyntaxKind.NullKeyword: | ||
| return nullOrUndefined(false); | ||
|
|
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| case ts.SyntaxKind.Identifier: | ||
| if ((right as ts.Identifier).text === "undefined") { | ||
| return nullOrUndefined(true); | ||
| } | ||
|
|
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| default: | ||
| return undefined; | ||
| } | ||
|
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| function nullOrUndefined(isUndefined: boolean): TypePredicate { | ||
| const flags = isStrictEquals | ||
| ? isUndefined ? undefinedFlags : ts.TypeFlags.Null | ||
| : (ts.TypeFlags.Null | undefinedFlags); | ||
| return { expression: left, predicate: flagPredicate(flags), isNullOrUndefined: true }; | ||
| } | ||
| } | ||
|
|
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| function isEmptyType(checker: ts.TypeChecker, type: ts.Type) { | ||
| return checker.typeToString(type) === "{}"; | ||
| } | ||
|
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| const undefinedFlags = ts.TypeFlags.Undefined | ts.TypeFlags.Void; | ||
|
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| interface TypePredicate { | ||
| expression: ts.Expression; | ||
| predicate: Predicate; | ||
| isNullOrUndefined: boolean; | ||
| } | ||
|
|
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| type Predicate = (type: ts.Type) => boolean; | ||
|
|
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| function getTypePredicateForKind(kind: string): Predicate { | ||
| switch (kind) { | ||
| case "undefined": | ||
| return flagPredicate(undefinedFlags); | ||
| case "boolean": | ||
| return flagPredicate(ts.TypeFlags.BooleanLike); | ||
| case "number": | ||
| return flagPredicate(ts.TypeFlags.NumberLike); | ||
| case "string": | ||
| return flagPredicate(ts.TypeFlags.StringLike); | ||
| case "symbol": | ||
| return flagPredicate(ts.TypeFlags.ESSymbol); | ||
| case "function": | ||
| return isFunction; | ||
| case "object": | ||
| // It's an object if it's not any of the above. | ||
| const allFlags = ts.TypeFlags.Undefined | ts.TypeFlags.Void | ts.TypeFlags.BooleanLike | | ||
| ts.TypeFlags.NumberLike | ts.TypeFlags.StringLike | ts.TypeFlags.ESSymbol; | ||
| return (type) => !Lint.isTypeFlagSet(type, allFlags) && !isFunction(type); | ||
| default: | ||
| return (_) => false; | ||
| } | ||
| } | ||
|
|
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| function flagPredicate(testedFlag: ts.TypeFlags): Predicate { | ||
| return (type) => Lint.isTypeFlagSet(type, testedFlag); | ||
| } | ||
|
|
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| function isFunction(t: ts.Type): boolean { | ||
| if (t.getCallSignatures().length !== 0) { | ||
| return true; | ||
| } | ||
| const symbol = t.getSymbol(); | ||
| return (symbol && symbol.getName()) === "Function"; | ||
| } | ||
|
|
||
| /** Returns a boolean value if that should always be the result of a type predicate. */ | ||
| function getConstantBoolean(type: ts.Type, predicate: (t: ts.Type) => boolean): boolean | undefined { | ||
| if (!Lint.isUnionType(type)) { | ||
| return predicate(type); | ||
| } | ||
|
|
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| let anyTrue = false; | ||
| let anyFalse = false; | ||
| for (const ty of type.types) { | ||
| if (predicate(ty)) { | ||
| anyTrue = true; | ||
| } else { | ||
| anyFalse = true; | ||
| } | ||
|
|
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| if (anyTrue && anyFalse) { | ||
| return undefined; | ||
| } | ||
| } | ||
|
|
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| return anyTrue; | ||
| } | ||
|
|
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| interface Equals { | ||
| isPositive: boolean; // True for "===" and "==" | ||
| isStrict: boolean; | ||
| } | ||
|
|
||
| function getEquals(kind: ts.SyntaxKind): Equals | undefined { | ||
| switch (kind) { | ||
| case ts.SyntaxKind.EqualsEqualsToken: | ||
| return { isPositive: true, isStrict: false }; | ||
| case ts.SyntaxKind.EqualsEqualsEqualsToken: | ||
| return { isPositive: true, isStrict: true }; | ||
| case ts.SyntaxKind.ExclamationEqualsToken: | ||
| return { isPositive: false, isStrict: false }; | ||
| case ts.SyntaxKind.ExclamationEqualsEqualsToken: | ||
| return { isPositive: false, isStrict: true }; | ||
| default: | ||
| return undefined; | ||
| } | ||
| } |
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