denoland/deno · error · AnyError

Found problem

Error message

Found {} problem{}

What it means

This is the terminal summary of `deno publish`'s 'slow types' check: the diagnostics collector counted N type-checking problems in the package's public API (typically exported functions/classes missing explicit return or parameter types), printed each one above, and now aborts the publish. JSR requires fully explicit types because it generates docs and .d.ts files without executing a type-checker on every consumer. Pass `--allow-slow-types` only if you accept the downsides listed in the message.

Solutions

1. Read the diagnostics printed above the summary; add explicit types to each flagged public/exported symbol (return types and parameter types).
2. Re-run `deno publish` (or `deno publish --dry-run`) until the check passes — dry-run runs the same diagnostics without uploading.
3. If the types genuinely cannot be made explicit and you accept slower consumer type-checking, no docs generation, and no .d.ts for Node, publish with `--allow-slow-types`.
4. Keep internals non-exported (remove `export`) so they are exempt from the public-API type requirements.

Example fix

// before
export function greet(name) {
  return `hello ${name}`;
}

// after
export function greet(name: string): string {
  return `hello ${name}`;
}

const cmd = new Deno.Command('deno', {
  args: ['publish', '--dry-run'],
});
const { code, stderr } = await cmd.output();
const text = new TextDecoder().decode(stderr);
const slowTypes = /Found \d+ problem/.test(text);
if (code !== 0 && slowTypes) {
  // fail early with the diagnostics; do not attempt the real publish
}

try {
  await runDeno(['publish']);
} catch (e) {
  if (/Found \d+ problem/.test(String(e.message))) {
    // parse the diagnostics above the summary and add explicit types,
    // or re-run with --allow-slow-types after a conscious decision
  }
}

When it happens

Trigger: `export function greet(name) { ... }` (no return/param types); `export const config = { ... }` whose inferred type is not nameable; re-exporting a value whose type cannot be computed from syntax alone; publishing with these diagnostics and without `--allow-slow-types`.

Common situations: Porting a quick prototype to JSR; TS code that relies on inference everywhere and compiled fine under `deno run`; version upgrades that tightened the slow-types rules so a package that published before now fails.

Related errors

• Cannot represent compiler option
• Cannot use --set-version when publishing a workspace…
• Checksum mismatch for
• Couldn't find a deno.json, deno.jsonc, jsr.json or…
• {}: {}

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/cc5ecc566434c8bc. Report an issue: GitHub.

Appendix: source

Thrown at cli/tools/publish/diagnostics.rs:68

      }
    }
    if errors > 0 {
      if has_slow_types_errors {
        log::error!(
          "This package contains errors for slow types. Fixing these errors will:\n"
        );
        log::error!(
          "  1. Significantly improve your package users' type checking performance."
        );
        log::error!("  2. Improve the automatic documentation generation.");
        log::error!("  3. Enable automatic .d.ts generation for Node.js.");
        log::error!(
          "\nDon't want to bother? You can choose to skip this step by"
        );
        log::error!("providing the --allow-slow-types flag.\n");
      }

      Err(anyhow!(
        "Found {} problem{}",
        errors,
        if errors == 1 { "" } else { "s" }
      ))
    } else {
      Ok(())
    }
  }

  pub fn has_error(&self) -> bool {
    self
      .diagnostics
      .lock()
      .iter()
      .any(|d| matches!(d.level(), DiagnosticLevel::Error))
  }

  pub fn push(&self, diagnostic: PublishDiagnostic) {

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