denoland/deno · error · anyhow::Error

Type checking failed: {}

Error message

Type checking failed:
{}

What it means

Generating declarations requires type-checking. `type_checker.emit_declarations` returns diagnostics, and if any diagnostic is present the tool bails with the full formatted diagnostic list embedded after the 'Type checking failed:' header.

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,

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Read the diagnostics after the header — each is `file(line,col): error TS####: message`; fix them top-down since the first error often cascades
2. Iterate with `deno check <same inputs>` — it surfaces the same diagnostics without re-running emit
3. If declarations are not needed, drop --declaration; plain transpile skips type-checking entirely

Example fix

// before (mod.ts)
export function add(a: number, b: string) { return a + b; }
// after
export function add(a: number, b: number): number { return a + b; }

# run the same type-check first; only transpile on a clean pass
deno check src/*.ts && deno transpile --declaration src/*.ts --outdir dist

# bash wrapper: surface diagnostics, fail loudly
if ! output=$(deno transpile --declaration src/mod.ts --outdir dist 2>&1); then
  echo "$output" | sed -n '/Type checking failed:/,$p'
  exit 1
fi

When it happens

Trigger: Any TypeScript type error in the input files (or their imports) while `--declaration` is active.

Common situations: Enabling --declaration on a codebase `deno check` never ran against; strictness differences between a file's scope and the default config; type errors surfaced from dependency .d.ts files.

Related errors

• No emittable files found. Only TypeScript/JSX/TSX files can
• Type checking failed.
• Found {} problem{}
• No input files specified
• Cannot use --output with multiple input files. Use --outdir

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/098ae781efab8651. Report an issue: GitHub.