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/
noUseBeforeDeclareRule.ts
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/
noUseBeforeDeclareRule.ts
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/**
* @license
* Copyright 2014 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 semver from "semver";
import { isBindingElement } from "tsutils";
import * as ts from "typescript";
import * as Lint from "../index";
import { codeExamples } from "./code-examples/noUseBeforeDeclare.examples";
export class Rule extends Lint.Rules.TypedRule {
/* tslint:disable:object-literal-sort-keys */
public static metadata: Lint.IRuleMetadata = {
ruleName: "no-use-before-declare",
description: "Disallows usage of variables before their declaration.",
descriptionDetails: Lint.Utils.dedent`
This rule is primarily useful when using the \`var\` keyword since the compiler will
automatically detect if a block-scoped \`let\` and \`const\` variable is used before
declaration. Since most modern TypeScript doesn't use \`var\`, this rule is generally
discouraged and is kept around for legacy purposes. It is slow to compute, is not
enabled in the built-in configuration presets, and should not be used to inform TSLint
design decisions.
`,
optionsDescription: "Not configurable.",
options: null,
optionExamples: [true],
type: "functionality",
typescriptOnly: false,
requiresTypeInfo: true,
codeExamples,
deprecationMessage: semver.gte(ts.version, "2.9.0-dev.0")
? "Since TypeScript 2.9. Please use the built-in compiler checks instead."
: undefined,
};
/* tslint:enable:object-literal-sort-keys */
public static FAILURE_STRING(name: string) {
return `variable '${name}' used before declaration`;
}
public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
return this.applyWithFunction(sourceFile, walk, undefined, program.getTypeChecker());
}
}
function walk(ctx: Lint.WalkContext, checker: ts.TypeChecker): void {
return ts.forEachChild(ctx.sourceFile, function recur(node: ts.Node): void {
switch (node.kind) {
case ts.SyntaxKind.TypeReference:
// Ignore types.
return;
case ts.SyntaxKind.PropertyAccessExpression:
// Ignore `y` in `x.y`, but recurse to `x`.
return recur((node as ts.PropertyAccessExpression).expression);
case ts.SyntaxKind.Identifier:
if (isPropNameInBinding(node)) {
return;
}
return checkIdentifier(node as ts.Identifier, checker.getSymbolAtLocation(node));
case ts.SyntaxKind.ExportSpecifier:
return checkIdentifier(
(node as ts.ExportSpecifier).name,
checker.getExportSpecifierLocalTargetSymbol(node as ts.ExportSpecifier),
);
default:
return ts.forEachChild(node, recur);
}
});
function checkIdentifier(node: ts.Identifier, symbol: ts.Symbol | undefined): void {
const declarations = symbol === undefined ? undefined : symbol.declarations;
if (declarations === undefined || declarations.length === 0) {
return;
}
const declaredBefore = declarations.some(decl => {
switch (decl.kind) {
case ts.SyntaxKind.FunctionDeclaration:
// Functions may be declared later.
return true;
default:
// Use `<=` in case this *is* the declaration.
// If it's a global declared in a different file, OK.
return decl.pos <= node.pos || decl.getSourceFile() !== ctx.sourceFile;
}
});
if (!declaredBefore) {
ctx.addFailureAtNode(node, Rule.FAILURE_STRING(node.text));
}
}
/**
* Destructured vars/args w/ rename are declared later in the source.
* var { x: y } = { x: 43 };
*/
function isPropNameInBinding(node: ts.Node): boolean {
return (
node.parent !== undefined &&
isBindingElement(node.parent) &&
node.parent.propertyName === node
);
}
}