How to programmatically lint code?

I’m currently working on a tool to quickly generate template code based on user preferences (https://github.com/AlCalzone/create-adapter). As part of this, I want to let the user choose his preferred style of quotes. For JS, this is quite easy using the ESLint API:

export function jsFixQuotes(sourceText: string, quotes: "single" | "double"): string {
	const linter = new Linter();
	const result = linter.verifyAndFix(sourceText, {
		// rules here...
	});
	return result.output;
}

I’ve been looking for a way to do that for TypeScript, but I can’t seem to find anything similar in the TSLint docs. Your project seems to support this, but I’m not sure how to use it programmatically.

Can you give me a pointer in the right direction?

[ajafff]

There you have it:

import * as ts from 'typescript';

export enum Quotemark {
    Single = "'",
    Double = '"',
}

export function fixQuotes(source: string, newQuotes: Quotemark) {
    const oldQuotes = newQuotes === Quotemark.Double ? Quotemark.Single : Quotemark.Double;
    // create an AST from the source code, this step is unnecessary if you already have a SourceFile object
    const sourceFile = ts.createSourceFile('quotes.ts', source, ts.ScriptTarget.Latest);
    let resultString = '';
    let lastPos = 0;

    // visit each immediate child node of SourceFile
    ts.forEachChild(sourceFile, function cb(node) {
        if (node.kind === ts.SyntaxKind.StringLiteral && source[node.end - 1] === oldQuotes) {
            // we found a string with the wrong quote style
            const start = node.getStart(sourceFile); // get the position of the opening quotes (this is different from 'node.pos' as it skips all whitespace and comments)
            const rawContent = source.slice(start + 1, node.end - 1); // get the actual contents of the string
            resultString += source.slice(lastPos, start) + newQuotes + escapeQuotes(rawContent, newQuotes, oldQuotes) + newQuotes;
            lastPos = node.end;
        } else {
            // recurse deeper down the AST visiting the immediate children of the current node
            ts.forEachChild(node, cb);
        }

    });
    resultString += source.slice(lastPos);

    return resultString;
}

/** Escape new quotes within the string, unescape the old quotes. */
function escapeQuotes(str: string, newQuotes: Quotemark, oldQuotes: Quotemark) {
    return str.replace(new RegExp(newQuotes, 'g'), `\\${newQuotes}`).replace(new RegExp(`\\\\${oldQuotes}`, 'g'), oldQuotes);
}

Feel free to use it in any way you want. I don’t claim any copyright on this snippet.

If you have any questions, just ask.

[ajafff]

If you could provide a snippet for that, I would be glad.

@AlCalzone sure thing. I’m trying to get this ready this evening or tomorrow morning.