microsoft/TypeScript · error · Error

There were no errors and declFiles generated did not match…

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.

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…
• Number of sourcemap files should be same as js files.
• No sourcemap files should be generated if inlineSourceMaps…
• Cannot have undefined value for compiler option
• Expected at least one js file to be emitted or at least one…

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

Appendix: 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))) {

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