Raise user error when Yarn is misconfigured

common/lib/dependabot/errors.rb

@@ -109,6 +109,27 @@ def initialize(source, msg = nil)
   # File level errors #
   #####################
 
+  class MisconfiguredTool < DependabotError
+    extend T::Sig
+
+    sig { returns(String) }
+    attr_reader :tool_name
+
+    sig do
+      params(
+        tool_name: String,
+        msg: String
+      ).void
+    end
+    def initialize(tool_name, msg)
+      @tool_name = tool_name
+
+      msg = "Dependabot detected that #{tool_name} is misconfigured in this repository. " \
+            "Running `#{tool_name.downcase}` results in the following error: #{msg}"
+      super(msg)
+    end
+  end
+
   class ToolVersionNotSupported < DependabotError
     extend T::Sig
 

npm_and_yarn/lib/dependabot/npm_and_yarn/helpers.rb

@@ -4,6 +4,8 @@
 module Dependabot
   module NpmAndYarn
     module Helpers
+      YARN_PATH_NOT_FOUND = /^.*(?<error>The "yarn-path" option has been set.*)/
+
       def self.npm_version(lockfile_content)
         "npm#{npm_version_numeric(lockfile_content)}"
       end
@@ -57,6 +59,15 @@ def self.yarn_major_version
       def self.fetch_yarn_major_version
         output = SharedHelpers.run_shell_command("yarn --version")
         Version.new(output).major
+      rescue SharedHelpers::HelperSubprocessFailed => e
+        message = e.message
+
+        if YARN_PATH_NOT_FOUND.match?(message)
+          error = T.must(T.must(YARN_PATH_NOT_FOUND.match(message))[:error]).gsub(Dir.pwd, ".")
+          raise MisconfiguredTool.new("Yarn", error)
+        end
+
+        raise
       end
 
       def self.yarn_zero_install?

npm_and_yarn/spec/dependabot/npm_and_yarn/update_checker/version_resolver_spec.rb

@@ -80,6 +80,28 @@
   describe "#latest_resolvable_version" do
     subject { resolver.latest_resolvable_version }
 
+    context "with a misconfigured yarn-berry project" do
+      let(:project_name) { "yarn_berry/misconfigured" }
+      let(:latest_allowable_version) { Gem::Version.new("1.3.0") }
+      let(:dependency) do
+        Dependabot::Dependency.new(
+          name: "left-pad",
+          version: "1.0.1",
+          requirements: [{
+            file: "package.json",
+            requirement: "^1.0.1",
+            groups: ["dependencies"],
+            source: { type: "registry", url: "https://registry.npmjs.org" }
+          }],
+          package_manager: "npm_and_yarn"
+        )
+      end
+
+      it "raises a Dependabot::MisconfiguredTool error" do
+        expect { subject }.to raise_error(Dependabot::MisconfiguredTool)
+      end
+    end
+
     context "with an npm 8 package-lock.json using the v3 lockfile format" do
       context "updating a dependency without peer dependency issues" do
         let(:project_name) { "npm8/package-lock-v3" }

npm_and_yarn/spec/fixtures/projects/yarn_berry/misconfigured/.yarnrc.yml

@@ -0,0 +1 @@
+yarnPath: .yarn/releases/yarn-3.5.1.cjs

npm_and_yarn/spec/fixtures/projects/yarn_berry/misconfigured/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "original",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "is-positive": "3.1.0",
+    "left-pad": "^1.0.1"
+  },
+  "packageManager": "yarn@3.5.1"
+}

npm_and_yarn/spec/fixtures/projects/yarn_berry/misconfigured/yarn.lock

@@ -0,0 +1,29 @@
+# This file is generated by running "yarn install" inside your project.
+# Manual changes might be lost - proceed with caution!
+
+__metadata:
+  version: 6
+  cacheKey: 8
+
+"is-positive@npm:3.1.0":
+  version: 3.1.0
+  resolution: "is-positive@npm:3.1.0"
+  checksum: 3675229110735f470860b5fe0740dae1baa9d6f7c6a69f25116aa1888cbc3d092f068f6f94219c290022d0e334f1c82db3041286236ae8a8e132146fd7bcf99d
+  languageName: node
+  linkType: hard
+
+"left-pad@npm:^1.0.1":
+  version: 1.3.0
+  resolution: "left-pad@npm:1.3.0"
+  checksum: 13fa96e17b70a54836490de22d4bab706e2ed508338bbabecfac72ecce445a74139c5b009a8112252cab8fc4ab7ac4ebd870e5b35bd236b443b12be96f8745ac
+  languageName: node
+  linkType: hard
+
+"original@workspace:.":
+  version: 0.0.0-use.local
+  resolution: "original@workspace:."
+  dependencies:
+    is-positive: 3.1.0
+    left-pad: ^1.0.1
+  languageName: unknown
+  linkType: soft

updater/lib/dependabot/update_files_command.rb

@@ -112,6 +112,11 @@ def handle_parser_error(error)
             "error-type": "git_dependencies_not_reachable",
             "error-detail": { "dependency-urls": error.dependency_urls }
           }
+        when Dependabot::MisconfiguredTool
+          {
+            "error-type": "misconfigured_tool",
+            "error-detail": { "tool-name": error.tool_name, message: error.message }
+          }
         when Dependabot::NotImplemented
           {
             "error-type": "not_implemented",