What causes "${fileName}(${line},${col}): ${message}" in microsoft/TypeScript?

Use the line,column in the message to jump to the exact token in the test file.

microsoft/TypeScript · error · Error

${fileName}(${line},${col}): ${message}

Error message

${fileName}(${line},${col}): ${message}

What it means

reportError is a generic formatting helper (not a single condition) that throws an Error with the form fileName(line,col): message. It is invoked from seven sites in fourslash test parsing: unparseable object markers, empty object markers, duplicate markers, range-end-without-start, unterminated ranges, and unterminated markers. The message text after the position prefix identifies which structural problem was found in the test source.

Source

Thrown at src/harness/fourslashImpl.ts:4857

        files,
        symlinks,
        ranges,
    };
}

function isConfig(file: FourSlashFile): boolean {
    return Harness.getConfigNameFromFileName(file.fileName) !== undefined;
}

const enum State {
    none,
    inSlashStarMarker,
    inObjectMarker,
}

function reportError(fileName: string, line: number, col: number, message: string): never {
    const errorMessage = fileName + "(" + line + "," + col + "): " + message;
    throw new Error(errorMessage);
}

function recordObjectMarker(fileName: string, location: LocationInformation, text: string, markerMap: Map<string, Marker>, markers: Marker[]): Marker | undefined {
    let markerValue;
    try {
        // Attempt to parse the marker value as JSON
        markerValue = JSON.parse("{ " + text + " }") as { name?: unknown; };
    }
    catch (e) {
        reportError(fileName, location.sourceLine, location.sourceColumn, "Unable to parse marker text " + e.message);
    }

    if (markerValue === undefined) {
        reportError(fileName, location.sourceLine, location.sourceColumn, "Object markers can not be empty");
    }

    const marker: Marker = {
        fileName,

View on GitHub (pinned to b465fdbfe1)

Solutions

Use the line,column in the message to jump to the exact token in the test file.
Match the trailing message to the condition: 'Unable to parse marker text' -> fix the JSON in the object marker; 'Object markers can not be empty' -> add content; 'Marker ... is duplicated' -> rename one; 'Found range end with no matching start' -> add an opening [|; 'Unterminated range' / 'Unterminated marker' -> add the matching close.
Re-validate the file with a fourslash linter or by comparing against a known-good test.

Example fix

// before — unterminated range
// [|const x = 1;
// const y = 2;
// after
// [|const x = 1;|]
// const y = 2;

Defensive patterns

Strategy: validation

Validate before calling

// Validate marker/range balance before running the test
function validateMarkers(content: string) {
    const openRanges = (content.match(/\[\|/g) || []).length;
    const closeRanges = (content.match(/\|\]/g) || []).length;
    if (openRanges !== closeRanges) throw new Error(`Unbalanced ranges: ${openRanges} open vs ${closeRanges} close`);
    const openMarkers = (content.match(/\/\*</g) || []).length;
    const closeMarkers = (content.match(/\*>\//g) || []).length;
    if (openMarkers !== closeMarkers) throw new Error(`Unbalanced markers`);
}

Prevention

Always close every [| with a |] and every /*<...>*/ marker in the same edit.
Use a fourslash-aware editor extension or linter to catch malformed marker/range syntax before running.

When it happens

Trigger: Any malformed fourslash marker/range syntax during parseFileContent: object marker text that fails JSON.parse, an empty object marker, two markers sharing the same name, a range close [| without a matching open, a [| ... range never closed, or a /*<...>*/ marker never closed.

Common situations: Hand-editing fourslash test files and breaking marker syntax — e.g. unbalanced [| |] pairs, malformed JSON inside object markers, or duplicate marker names across the file. The error pinpoints the line and column of the offending token.

Related errors

AI-assisted analysis of microsoft/TypeScript@b465fdbfe1 (2026-08-12). Data as JSON: /api/errors/5cffbb2597c63baf. Report an issue: GitHub.