microsoft/TypeScript · error · Error

verifyCurrentLineContent\n

Error message

verifyCurrentLineContent\n

What it means

Assertion failure in the four-phase test harness (`src/harness/fourslashImpl.ts`). `verifyCurrentLineContent(text)` recomputes the line under the caret and compares it to `text`; on mismatch it throws `Error("verifyCurrentLineContent\n" + expected-vs-actual). This is a test-authoring assertion, not production code.

Source

Thrown at src/harness/fourslashImpl.ts:3038

        const actual = this.getIndentation(this.activeFile.fileName, this.currentCaretPosition, indentStyle, baseIndentSize);
        const lineCol = this.getLineColStringAtPosition(this.currentCaretPosition);
        if (actual !== numberOfSpaces) {
            this.raiseError(`verifyIndentationAtCurrentPosition failed at ${lineCol} - expected: ${numberOfSpaces}, actual: ${actual}`);
        }
    }

    public verifyIndentationAtPosition(fileName: string, position: number, numberOfSpaces: number, indentStyle: ts.IndentStyle = ts.IndentStyle.Smart, baseIndentSize = 0): void {
        const actual = this.getIndentation(fileName, position, indentStyle, baseIndentSize);
        const lineCol = this.getLineColStringAtPosition(position);
        if (actual !== numberOfSpaces) {
            this.raiseError(`verifyIndentationAtPosition failed at ${lineCol} - expected: ${numberOfSpaces}, actual: ${actual}`);
        }
    }

    public verifyCurrentLineContent(text: string): void {
        const actual = this.getCurrentLineContent();
        if (actual !== text) {
            throw new Error("verifyCurrentLineContent\n" + displayExpectedAndActualString(text, actual, /*quoted*/ true));
        }
    }

    public verifyCurrentFileContent(text: string): void {
        this.verifyFileContent(this.activeFile.fileName, text);
    }

    private verifyFileContent(fileName: string, text: string) {
        const actual = this.getFileContent(fileName);
        if (actual !== text) {
            throw new Error(`verifyFileContent in file '${fileName}' failed:\n${showTextDiff(text, actual)}`);
        }
    }

    public verifyFormatDocumentChangesNothing(): void {
        const { fileName } = this.activeFile;
        const before = this.getFileContent(fileName);
        this.formatDocument();

View on GitHub (pinned to b465fdbfe1)

Solutions

1. Copy the actual line from the failure diff into the expected `text`.
2. Re-check marker positions — the harness uses the caret to find the line.
3. Account for indentation: the expected string must include leading whitespace.
4. If the new behavior is correct, update the test; if not, fix the feature.

Example fix

// before
fourshaft.verifyCurrentLineContent("const x = 1;"); // actual has different indent/text
// after
fourshaft.verifyCurrentLineContent("    const x = 1;");  // copied from actual

When it happens

Trigger: Writing a Fourslash test where the marker positions or expected text don't match what the language service produced after an edit/completion. The harness finds the current line from the caret marker, so wrong marker placement also triggers it.

Common situations: Updating Fourslash baselines after a formatting/indentation behavior change; off-by-one marker placement; expected string that doesn't include leading indentation; behavior change in completion/format that wasn't reflected in the test.

Related errors

• verifyFileContent in file '${fileName}' failed:\n${showTextD
• verifyTextAtCaretIs\n
• You need to change the source code of fourslash test to use
• Exactly one refactor range is allowed per test.
• File index (${index}) in openFile was out of range. There ar

AI-assisted analysis of microsoft/TypeScript@b465fdbfe1 (2026-08-12). Data as JSON: /api/errors/bb37583c6dd86bb3. Report an issue: GitHub.