Bottles: allow skipping or_later tags

This is a developer-only feature, so it's gated via `HOMEBREW_DEVELOPER`.
This is intended to enable testing of macOS 10.15; users building software
manually to test compatibility of early betas need to be able to build
software from source instead of via pouring 10.14 bottles. This isn't
intended to be a general-purpose `HOMEBREW_BUILD_FROM_SOURCE` replacement,
and has no effect on released versions of macOS.

Library/Homebrew/extend/ARGV.rb

@@ -123,6 +123,10 @@ module HomebrewArgvExtension
     !ENV["HOMEBREW_DEVELOPER"].nil?
   end
 
+  def skip_or_later_bottles?
+    homebrew_developer? && !ENV["HOMEBREW_SKIP_OR_LATER_BOTTLES"].nil?
+  end
+
   def no_sandbox?
     include?("--no-sandbox") || !ENV["HOMEBREW_NO_SANDBOX"].nil?
   end

Library/Homebrew/extend/os/mac/utils/bottles.rb

@@ -16,8 +16,13 @@ module Utils
       alias generic_find_matching_tag find_matching_tag
 
       def find_matching_tag(tag)
-        generic_find_matching_tag(tag) ||
-          find_older_compatible_tag(tag)
+        # Used primarily by developers testing beta macOS releases.
+        if OS::Mac.prerelease? && ARGV.skip_or_later_bottles?
+          generic_find_matching_tag(tag)
+        else
+          generic_find_matching_tag(tag) ||
+            find_older_compatible_tag(tag)
+        end
       end
 
       def tag_without_or_later(tag)

Library/Homebrew/test/utils/bottles/collector_spec.rb

@@ -20,9 +20,25 @@ describe Utils::Bottles::Collector do
     end
 
     it "uses older tags when needed", :needs_macos do
-      subject[:yosemite] = "foo"
-      expect(subject.fetch_checksum_for(:yosemite)).to eq(["foo", :yosemite])
-      expect(subject.fetch_checksum_for(:mavericks)).to be nil
+      subject[:mavericks] = "foo"
+      expect(subject.send(:find_matching_tag, :mavericks)).to eq(:mavericks)
+      expect(subject.send(:find_matching_tag, :yosemite)).to eq(:mavericks)
+    end
+
+    it "does not use older tags when requested not to", :needs_macos do
+      allow(ARGV).to receive(:skip_or_later_bottles?).and_return(true)
+      allow(OS::Mac).to receive(:prerelease?).and_return(true)
+      subject[:mavericks] = "foo"
+      expect(subject.send(:find_matching_tag, :mavericks)).to eq(:mavericks)
+      expect(subject.send(:find_matching_tag, :yosemite)).to be_nil
+    end
+
+    it "ignores HOMEBREW_SKIP_OR_LATER_BOTTLES on release versions", :needs_macos do
+      allow(ARGV).to receive(:skip_or_later_bottles?).and_return(true)
+      allow(OS::Mac).to receive(:prerelease?).and_return(false)
+      subject[:mavericks] = "foo"
+      expect(subject.send(:find_matching_tag, :mavericks)).to eq(:mavericks)
+      expect(subject.send(:find_matching_tag, :yosemite)).to eq(:mavericks)
     end
   end
 end