Allow docker version prefixes to contain underscores

docker/lib/dependabot/docker/tag.rb

@@ -9,8 +9,8 @@ class Tag
       WORDS_WITH_BUILD = /(?:(?:-[a-z]+)+-[0-9]+)+/
       VERSION_REGEX = /v?(?<version>[0-9]+(?:\.[0-9]+)*(?:_[0-9]+|\.[a-z0-9]+|#{WORDS_WITH_BUILD}|-(?:kb)?[0-9]+)*)/i
       VERSION_WITH_SFX = /^#{VERSION_REGEX}(?<suffix>-[a-z][a-z0-9.\-]*)?$/i
-      VERSION_WITH_PFX = /^(?<prefix>[a-z][a-z0-9.\-]*-)?#{VERSION_REGEX}$/i
-      VERSION_WITH_PFX_AND_SFX = /^(?<prefix>[a-z\-]+-)?#{VERSION_REGEX}(?<suffix>-[a-z\-]+)?$/i
+      VERSION_WITH_PFX = /^(?<prefix>[a-z][a-z0-9.\-_]*-)?#{VERSION_REGEX}$/i
+      VERSION_WITH_PFX_AND_SFX = /^(?<prefix>[a-z\-_]+-)?#{VERSION_REGEX}(?<suffix>-[a-z\-]+)?$/i
       NAME_WITH_VERSION =
         /
           #{VERSION_WITH_PFX}|

docker/spec/dependabot/docker/file_parser_spec.rb

@@ -462,6 +462,34 @@
       end
     end
 
+    context "with a _ in the tag" do
+      let(:dockerfile_fixture_name) { "underscore" }
+
+      its(:length) { is_expected.to eq(1) }
+
+      describe "the first dependency" do
+        subject(:dependency) { dependencies.first }
+        let(:expected_requirements) do
+          [{
+            requirement: nil,
+            groups: [],
+            file: "Dockerfile",
+            source: {
+              registry: "registry-host.io:5000",
+              tag: "someRepo_19700101.4"
+            }
+          }]
+        end
+
+        it "has the right details" do
+          expect(dependency).to be_a(Dependabot::Dependency)
+          expect(dependency.name).to eq("myreg/ubuntu")
+          expect(dependency.version).to eq("someRepo_19700101.4")
+          expect(dependency.requirements).to eq(expected_requirements)
+        end
+      end
+    end
+
     context "with a private registry and a tag" do
       let(:dockerfile_fixture_name) { "private_tag" }
 

docker/spec/fixtures/docker/dockerfiles/underscore

@@ -0,0 +1,18 @@
+FROM registry-host.io:5000/myreg/ubuntu:someRepo_19700101.4
+
+### SYSTEM DEPENDENCIES
+
+RUN apt-get update \
+    && apt-get upgrade -y \
+    && apt-get install -y --no-install-recommends \
+      build-essential \
+      dirmngr \
+      git \
+
+### RUBY
+
+# Install Ruby 2.4
+RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys C3173AA6 \
+    && echo "deb http://ppa.launchpad.net/brightbox/ruby-ng/ubuntu zesty main" > /etc/apt/sources.list.d/brightbox.list \
+    && apt-get update
+RUN apt-get install -y ruby2.4 ruby2.4-dev