microsoft/TypeScript · error · Error

There were no errors and declFiles generated did not match n

Error message

There were no errors and declFiles generated did not match number of js files generated

What it means

Thrown by prepareDeclarationCompilationContext when declaration:true, emitDeclarationOnly is not set, compilation produced no errors, but the number of declaration files (result.dts.size) does not equal the number of JS files (getNumberOfJsFiles excluding JSON). The harness expects a one-to-one correspondence between .d.ts and .js outputs for declaration-emit tests.

Source

Thrown at src/harness/harnessIO.ts:407

    }

    export function prepareDeclarationCompilationContext(
        inputFiles: readonly TestFile[],
        otherFiles: readonly TestFile[],
        result: compiler.CompilationResult,
        harnessSettings: TestCaseParser.CompilerSettings & HarnessOptions,
        options: ts.CompilerOptions,
        // Current directory is needed for rwcRunner to be able to use currentDirectory defined in json file
        currentDirectory: string | undefined,
    ): DeclarationCompilationContext | undefined {
        if (options.declaration && result.diagnostics.length === 0) {
            if (options.emitDeclarationOnly) {
                if (result.js.size > 0 || (result.dts.size === 0 && !options.noEmit)) {
                    throw new Error("Only declaration files should be generated when emitDeclarationOnly:true");
                }
            }
            else if (result.dts.size !== result.getNumberOfJsFiles(/*includeJson*/ false)) {
                throw new Error("There were no errors and declFiles generated did not match number of js files generated");
            }
        }

        const declInputFiles: TestFile[] = [];
        const declOtherFiles: TestFile[] = [];

        // if the .d.ts is non-empty, confirm it compiles correctly as well
        if (options.declaration && result.diagnostics.length === 0 && result.dts.size > 0) {
            ts.forEach(inputFiles, file => addDtsFile(file, declInputFiles));
            ts.forEach(otherFiles, file => addDtsFile(file, declOtherFiles));
            return { declInputFiles, declOtherFiles, harnessSettings, options, currentDirectory: currentDirectory || harnessSettings.currentDirectory };
        }

        function addDtsFile(file: TestFile, dtsFiles: TestFile[]) {
            if (vpath.isDeclaration(file.unitName) || vpath.isJson(file.unitName)) {
                dtsFiles.push(file);
            }
            else if (vpath.isTypeScript(file.unitName) || (vpath.isJavaScript(file.unitName) && ts.getAllowJSCompilerOption(options))) {

View on GitHub (pinned to b465fdbfe1)

Solutions

1. List result.dts and result.js contents to identify which files are missing a counterpart.
2. If a compiler change intentionally altered the pairing, update the test expectations accordingly.
3. If a file legitimately emits only JS (e.g. a .js input), exclude it from the declaration test inputs or adjust the harness count.

// Verify the 1:1 dts/js correspondence before declaration baselining
if (options.declaration && !options.emitDeclarationOnly && result.diagnostics.length === 0) {
    if (result.dts.size !== result.getNumberOfJsFiles(false)) {
        throw new Error(`dts=${result.dts.size} js=${result.getNumberOfJsFiles(false)} mismatch`);
    }
}

When it happens

Trigger: A declaration-emit test compiles cleanly but produces a different count of .d.ts files than .js files — e.g. some files emit JS but no declaration, or vice versa. result.dts.size !== result.getNumberOfJsFiles(false).

Common situations: A compiler change alters declaration emit granularity (e.g. .d.ts merging or splitting), a test includes files that emit JS but are not declaration candidates, or a transform drops declarations for some files. Often signals a real compiler behaviour change rather than a config typo.

Related errors

• Only declaration files should be generated when emitDeclarat
• Number of sourcemap files should be same as js files.
• No sourcemap files should be generated if inlineSourceMaps w
• Cannot have undefined value for compiler option '${name}'.
• Unknown value '${value}' for compiler option '${name}'.

AI-assisted analysis of microsoft/TypeScript@b465fdbfe1 (2026-08-12). Data as JSON: /api/errors/8b277b6c7b4299db. Report an issue: GitHub.