denoland/deno · error · Error

Linter plugin ${plugin.name} has already been registered

Error message

Linter plugin ${plugin.name} has already been registered

What it means

Thrown by installPlugin() in cli/js/40_lint.js when a plugin with the same `name` was already registered in this linter instance (state.installedPlugins). Rule ids are namespaced as `pluginName/ruleName`, so a second plugin with the same name would collide with the first. Unlike the shape errors, this message carries no specifier prefix.

Source

Thrown at cli/js/40_lint.js:507

    throw new Error(
      `${prefix}Linter plugin name must only contain lowercase letters (a-z) or hyphens (-).`,
    );
  }
  if (plugin.name.startsWith("-") || plugin.name.endsWith("-")) {
    throw new Error(
      `${prefix}Linter plugin name must start and end with a lowercase letter.`,
    );
  }
  if (plugin.name.includes("--")) {
    throw new Error(
      `${prefix}Linter plugin name must not have consequtive hyphens.`,
    );
  }
  if (typeof plugin.rules !== "object") {
    throw new Error(`${prefix}Linter plugin rules must be an object`);
  }
  if (state.installedPlugins.has(plugin.name)) {
    throw new Error(`Linter plugin ${plugin.name} has already been registered`);
  }
  state.plugins.push(plugin);
  state.installedPlugins.add(plugin.name);

  return {
    name: plugin.name,
    ruleNames: Object.keys(plugin.rules),
  };
}

/**
 * @param {AstContext} ctx
 * @param {number} idx
 * @returns {FacadeNode | null}
 */
function getNode(ctx, idx) {
  if (idx === AST_IDX_INVALID) return null;
  const cached = ctx.nodes.get(idx);

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Remove the duplicate entry from `lint.plugins` so each plugin name is registered once
2. If two distinct plugins share a name, rename one of them to a unique lowercase name
3. If you re-export plugins through a barrel module, make sure the barrel is not listed alongside its targets

Example fix

// deno.json before
{
  "lint": {
    "plugins": ["jsr:@corp/lint", "./lint/index.ts"]
  }
}

// deno.json after
{
  "lint": {
    "plugins": ["jsr:@corp/lint"]
  }
}

const seen = new Set();
for (const p of plugins) {
  if (seen.has(p.name)) {
    throw new Error(`duplicate lint plugin name: '${p.name}' listed twice`);
  }
  seen.add(p.name);
}

function hasUniqueNames(plugins) {
  const names = plugins.map((p) => p.name);
  return new Set(names).size === names.length;
}

When it happens

Trigger: Listing the same plugin twice in `lint.plugins` in deno.json (directly or via two re-exporting modules); shipping two different plugins that both declare name: "recommended"; importing a plugin and also bundling a local copy of it.

Common situations: A config that loads a plugin both from jsr/npm and from a local path; a monorepo where two teams wrote plugins with the same generic name ("lint", "helpers"); stale duplicate entries after refactoring the plugin list.

Related errors

• ${prefix}Linter plugin name must only contain lowercase lett
• ${prefix}Linter plugin name must start and end with a lowerc
• ${prefix}Linter plugin name must not have consequtive hyphen
• ${prefix}Linter plugin rules must be an object
• Visitor "${name}" of plugin "${id}" errored

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/e532b2d8236595a9. Report an issue: GitHub.