Fix migrations of formulae and casks to non homebrew taps

Library/Homebrew/cask/cask_loader.rb

@@ -458,6 +458,7 @@ module Cask
 
         loaders = Tap.select { |tap| tap.installed? && !tap.core_cask_tap? }
                      .filter_map { |tap| super("#{tap}/#{token}", warn:) }
+                     .uniq(&:path)
                      .select { |tap| tap.path.exist? }
 
         case loaders.count

Library/Homebrew/formulary.rb

@@ -828,6 +828,7 @@ module Formulary
 
       loaders = Tap.select { |tap| tap.installed? && !tap.core_tap? }
                    .filter_map { |tap| super("#{tap}/#{name}", warn:) }
+                   .uniq(&:path)
                    .select { |tap| tap.path.exist? }
 
       case loaders.count

Library/Homebrew/test/cask/cask_loader_spec.rb

@@ -82,6 +82,41 @@ RSpec.describe Cask::CaskLoader, :cask do
           (old_tap.path/"tap_migrations.json").write tap_migrations.to_json
         end
 
+        context "to a cask in an other tap" do
+          # Can't use local-caffeine. It is a fixture in the :core_cask_tap and would take precendence over :new_tap.
+          let(:token) { "some-cask" }
+
+          let(:old_tap) { Tap.fetch("homebrew", "foo") }
+          let(:new_tap) { Tap.fetch("homebrew", "bar") }
+
+          let(:cask_file) { new_tap.cask_dir/"#{token}.rb" }
+
+          before do
+            new_tap.cask_dir.mkpath
+            FileUtils.touch cask_file
+          end
+
+          # FIXME
+          # It would be preferable not to print a warning when installing with the short token
+          it "warns when loading the short token" do
+            expect do
+              described_class.for(token)
+            end.to output(%r{Cask #{old_tap}/#{token} was renamed to #{new_tap}/#{token}\.}).to_stderr
+          end
+
+          it "does not warn when loading the full token in the new tap" do
+            expect do
+              described_class.for("#{new_tap}/#{token}")
+            end.not_to output.to_stderr
+          end
+
+          it "warns when loading the full token in the old tap" do
+            expect do
+              described_class.for("#{old_tap}/#{token}")
+            end.to output(%r{Cask #{old_tap}/#{token} was renamed to #{new_tap}/#{token}\.}).to_stderr
+          end
+        end
+
         context "to a formula in the default tap" do
           let(:old_tap) { core_cask_tap }
           let(:new_tap) { core_tap }

Library/Homebrew/test/formulary_spec.rb

@@ -641,6 +641,45 @@ RSpec.describe Formulary do
           #   end
           # end
         end
+
+        context "to a third-party tap" do
+          let(:old_tap) { Tap.fetch("another", "foo") }
+          let(:new_tap) { Tap.fetch("another", "bar") }
+          let(:formula_file) { new_tap.formula_dir/"#{token}.rb" }
+
+          before do
+            new_tap.formula_dir.mkpath
+            FileUtils.touch formula_file
+          end
+
+          after do
+            FileUtils.rm_rf Tap::TAP_DIRECTORY/"another"
+          end
+
+          # FIXME
+          # It would be preferable not to print a warning when installing with the short token
+          it "warns when loading the short token" do
+            expect do
+              described_class.loader_for(token)
+            end.to output(
+              a_string_including("Formula #{old_tap}/#{token} was renamed to #{new_tap}/#{token}.").once,
+            ).to_stderr
+          end
+
+          it "does not warn when loading the full token in the new tap" do
+            expect do
+              described_class.loader_for("#{new_tap}/#{token}")
+            end.not_to output.to_stderr
+          end
+
+          it "warns when loading the full token in the old tap" do
+            expect do
+              described_class.loader_for("#{old_tap}/#{token}")
+            end.to output(
+              a_string_including("Formula #{old_tap}/#{token} was renamed to #{new_tap}/#{token}.").once,
+            ).to_stderr
+          end
+        end
       end
     end
   end