version: parse tag if detecting version

Library/Homebrew/test/version_spec.rb

@@ -684,10 +684,15 @@ describe Version do
         .to be_detected_from("https://php.net/get/php-7.1.10.tar.gz/from/this/mirror")
     end
 
-    specify "from URL" do
+    specify "from tag" do
       expect(described_class.create("1.2.3"))
         .to be_detected_from("https://github.com/foo/bar.git", tag: "v1.2.3")
     end
+
+    specify "beta from tag" do
+      expect(described_class.create("1.2.3-beta1"))
+        .to be_detected_from("https://github.com/foo/bar.git", tag: "v1.2.3-beta1")
+    end
   end
 end
 

Library/Homebrew/version.rb

@@ -201,7 +201,7 @@ class Version
 
   def self.detect(url, specs)
     if specs.key?(:tag)
-      FromURL.new(specs[:tag][/((?:\d+\.)*\d+)/, 1])
+      FromURL.parse(specs[:tag])
     else
       FromURL.parse(url)
     end