denoland/deno · error

Type checking failed when generating declarations:\n{}

Error message

Type checking failed when generating declarations:\n{}

What it means

deno bundle --declaration runs the TypeScript compiler over the entry's module graph to emit .d.ts files (type_checker.emit_declarations, cli/tools/bundle/mod.rs:460-466). If tsc produces any diagnostics, the run fails with them appended after this message - the same class of errors deno check reports, surfaced from bundling.

Source

Thrown at cli/tools/bundle/mod.rs:469

      specifiers,
      crate::graph_util::BuildGraphWithNpmOptions {
        is_dynamic: false,
        loader: None,
        npm_caching: cli_options.default_npm_caching_strategy(),
      },
    )
    .await?;

  // Run type checker to emit declaration files
  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() {
    deno_core::anyhow::bail!(
      "Type checking failed when generating declarations:\n{}",
      result.diagnostics
    );
  }

  // Index emitted .d.ts files by their original source specifier
  // TSC emits keys like "file:///path/to/file.d.ts" - map them back to source paths
  let mut dts_by_source: std::collections::HashMap<String, String> =
    std::collections::HashMap::new();
  for (file_name, content) in &result.emitted_files {
    // Map "file:///path/to/mod.d.ts" -> normalized source path
    if let Ok(specifier) = Url::parse(file_name)
      && let Ok(file_path) = specifier.to_file_path()
    {
      let source_path = file_path.to_string_lossy().to_string();
      dts_by_source.insert(source_path, content.clone());
    }
  }

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Run 'deno check <entry>' and fix the reported type errors there first - it iterates faster than bundling
2. Ensure npm:/jsr: dependencies expose types (prefer @types/ packages where the base package is untyped)
3. Loosen the specific code: correct the typing rather than suppressing; as a last resort annotate with @ts-ignore/@ts-expect-error at the exact sites listed in the diagnostics
4. If the declaration artifact isn't required, drop the --declaration flag from the build step

Example fix

# before
deno bundle --declaration src/lib/main.ts --outdir dist  # fails: Type checking failed when generating declarations
# after: iterate on errors first, then bundle
deno check src/lib/main.ts   # fix everything reported here first
deno bundle --declaration src/lib/main.ts --outdir dist

# Validate type-cleanness before the declaration bundle step
deno check src/lib/main.ts || { echo 'fix type errors before --declaration'; exit 1; }
deno bundle --declaration src/lib/main.ts --outdir dist

# CI: run declaration bundling only when the graph type-checks
if deno check src/lib/main.ts; then deno bundle --declaration src/lib/main.ts --outdir dist; else echo 'skipping --declaration: type errors present'; exit 1; fi

When it happens

Trigger: Any type error in the entry's graph (TS2322 assignments, TS2339 property access, TS2307 missing modules with types missing); npm/jsr dependencies that ship no or broken types; tsconfig compilerOptions (strictness, lib) making previously-passing code fail.

Common situations: Libraries bundling artifacts with --declaration in CI where local editor checks were skipped; a dependency update changing types; strict mode enabled via deno.json compilerOptions turning previously silent issues into errors.

Related errors

• No declaration file emitted for entry point: {}
• Entry point must be a file: {}
• The bench function must have a name
• ${prefix}Linter plugin name must be a string
• Invalid cron schedule: start=${start}, end=${end}, every=${e

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/620045b69a0e1bbb. Report an issue: GitHub.