improving error message

common/lib/dependabot/errors.rb

@@ -661,6 +661,23 @@ def initialize(dependencies)
     end
   end
 
+  class UnresolvableVersionError < DependabotError
+    extend T::Sig
+
+    sig { returns(T::Array[String]) }
+    attr_reader :dependencies
+
+    sig { params(dependencies: T::Array[String]).void }
+    def initialize(dependencies)
+      @dependencies = dependencies
+
+      msg = "Unable to determine semantic version from tags or commits for dependencies. " \
+            "Dependencies must have a tag or commit that references a semantic version. " \
+            "Affected dependencies: #{@dependencies.join(', ')}"
+      super(msg)
+    end
+  end
+
   class GitDependenciesNotReachable < DependabotError
     extend T::Sig
 

github_actions/lib/dependabot/github_actions/file_parser.rb

@@ -36,7 +36,7 @@ def parse
         end
 
         dependencies_without_version = dependency_set.dependencies.select { |dep| dep.version.nil? }
-        raise UpdateNotPossible, dependencies_without_version.map(&:name) unless dependencies_without_version.empty?
+        raise UnresolvableVersionError, dependencies_without_version.map(&:name) unless dependencies_without_version.empty?
 
         dependency_set.dependencies
       end

github_actions/spec/dependabot/github_actions/file_parser_spec.rb

@@ -572,10 +572,12 @@ def mock_service_pack_request(nwo)
         mock_service_pack_request("taiki-e/install-action")
       end
 
-      it "raises an UpdateNotPossible error" do
+      it "raises an UnresolvableVersionError error" do
         expect { parser.parse }.to raise_error(
-          Dependabot::UpdateNotPossible,
-          "The following dependencies could not be updated: taiki-e/install-action"
+          Dependabot::UnresolvableVersionError,
+          "Unable to determine semantic version from tags or commits for dependencies. " \
+          "Dependencies must have a tag or commit that references a semantic version. " \
+          "Affected dependencies: taiki-e/install-action"
         )
       end
     end