denoland/deno · error · AnyError

Type checking failed

Error message

Type checking failed:
{}

What it means

Declaration emit in Deno runs a full TSC type-check of the module graph first (`type_checker.emit_declarations`). If TSC returns any diagnostics, Deno bails with 'Type checking failed' followed by the formatted diagnostic list. This is the standard TypeScript error surface (TS2xxx codes) relayed during `deno cache`/declaration generation, not a Deno-internal failure.

Solutions

1. Read the diagnostics printed after the header and fix the listed type errors in the named files.
2. Run `deno check <entrypoint>` to reproduce and iterate on the same diagnostics quickly.
3. If the errors come from newly enabled compilerOptions, relax them or fix the code they now flag.
4. If you only need transpilation (not declarations), run without type-checking (e.g. `--no-check`) — but note declaration generation always requires a clean type-check.

Example fix

// before: type error that triggers the diagnostic
export const count: number = parseInt("1"); // ok, but:
export const bad: number = "1"; // TS2322

// after
export const bad: number = parseInt("1");

# fail fast on type errors before generating anything
deno check main.ts || { echo "fix type errors first"; exit 1; }
deno cache main.ts

output=$(deno cache main.ts 2>&1) || { echo "$output" | grep '^TS[0-9]' ; exit 1; }

When it happens

Trigger: Any TypeScript type error in the program being checked: bad imports types, wrong argument types, missing exports, `strict` violations, or errors in dependencies pulled into the graph. It fires as soon as `result.diagnostics.has_diagnostic()` is true after `emit_declarations` at cli/tools/transpile.rs:298.

Common situations: Running `deno cache` (with type-checking enabled) or emitting declarations on code that has never been `deno check`ed; tightening `strict`/`noUncheckedIndexedAccess` in deno.json compilerOptions and re-caching; upgrading Deno/TS versions that surface new diagnostics in previously-passing code.

Related errors

• Cannot generate declarations for files with different…
• Entry point must be a file
• Error getting navigation tree for
• Failed ensuring public API type output is valid.
• No declaration file emitted for entry point

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/098ae781efab8651. Report an issue: GitHub.

Appendix: source

Thrown at cli/tools/transpile.rs:298

         '{}' uses scope '{}' but '{}' uses scope '{}'.\n\
         Separate these files into different invocations.",
        first_specifier,
        first_key,
        specifier,
        key,
      );
    }
  }

  let type_checker = factory.type_checker().await?;
  let result = type_checker.emit_declarations(
    Arc::new(graph),
    root_names,
    cli_options.ts_type_lib_window(),
  )?;

  if result.diagnostics.has_diagnostic() {
    anyhow::bail!("Type checking failed:\n{}", result.diagnostics);
  }

  // Determine the output directory for .d.ts files.
  // With -o, place .d.ts next to the output file.
  // With --outdir, use the outdir.
  // Otherwise, place next to the source file (handled by TSC path).
  let output_base_dir = if let Some(output) = &transpile_flags.output {
    let output_path = cwd.join(output);
    output_path.parent().map(|p| p.to_path_buf())
  } else {
    None
  };

  // Write emitted .d.ts files
  for (file_name, content) in &result.emitted_files {
    // The file names from TSC are specifier-based, convert to output paths
    let output_path = resolve_dts_output_path(
      file_name,

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