Fix cask migration warnings.

Library/Homebrew/cask/cask_loader.rb

@@ -437,6 +437,23 @@ def from_h_gsubs(value, appdir)
       end
     end
 
+    # Loader which tries loading casks from the default tap.
+    class FromDefaultNameLoader < FromTapLoader
+      sig {
+        params(ref: T.any(String, Pathname, Cask, URI::Generic), warn: T::Boolean)
+          .returns(T.nilable(T.attached_class))
+      }
+      def self.try_new(ref, warn: false)
+        return unless ref.is_a?(String)
+        return unless (token = ref[HOMEBREW_DEFAULT_TAP_CASK_REGEX, :token])
+        return unless (tap = CoreCaskTap.instance).installed?
+
+        return unless (loader = super("#{tap}/#{token}", warn: warn))
+
+        loader if loader.path.exist?
+      end
+    end
+
     # Loader which tries loading casks from tap paths, failing
     # if the same token exists in multiple taps.
     class FromNameLoader < FromTapLoader
@@ -458,11 +475,6 @@ def self.try_new(ref, warn: false)
         when 1
           loaders.first
         when 2..Float::INFINITY
-          # Always prefer the default tap, i.e. behave the same as if loading from the API.
-          if (default_tap_loader = loaders.find { _1.tap.core_cask_tap? })
-            return default_tap_loader
-          end
-
           raise TapCaskAmbiguityError.new(token, loaders.map(&:tap))
         end
       end
@@ -555,6 +567,7 @@ def self.for(ref, need_path: false, warn: true)
         FromURILoader,
         FromAPILoader,
         FromTapLoader,
+        FromDefaultNameLoader,
         FromNameLoader,
         FromPathLoader,
         FromInstalledPathLoader,

Library/Homebrew/test/cask/cask_loader_spec.rb

@@ -66,5 +66,45 @@
         end
       end
     end
+
+    context "when not using the API" do
+      before do
+        ENV["HOMEBREW_NO_INSTALL_FROM_API"] = "1"
+      end
+
+      context "when a cask is migrated to the default tap" do
+        let(:token) { "local-caffeine" }
+        let(:tap_migrations) do
+          {
+            token => default_tap.name,
+          }
+        end
+        let(:old_tap) { CoreTap.instance }
+        let(:default_tap) { CoreCaskTap.instance }
+
+        before do
+          (old_tap.path/"tap_migrations.json").write tap_migrations.to_json
+          old_tap.clear_cache
+        end
+
+        it "does not warn when loading the short token" do
+          expect do
+            described_class.for(token)
+          end.not_to output.to_stderr
+        end
+
+        it "does not warn when loading the full token in the default tap" do
+          expect do
+            described_class.for("#{default_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 #{token}\.}).to_stderr
+        end
+      end
+    end
   end
 end

Library/Homebrew/test/formulary_spec.rb

@@ -528,4 +528,47 @@ def formula_json_contents(extra_items = {})
       expect(described_class.convert_to_string_or_symbol(":foo")).to eq :foo
     end
   end
+
+  describe "::loader_for" do
+    context "when not using the API" do
+      before do
+        ENV["HOMEBREW_NO_INSTALL_FROM_API"] = "1"
+      end
+
+      context "when a formula is migrated to the default tap" do
+        let(:token) { "local-caffeine" }
+        let(:tap_migrations) do
+          {
+            token => default_tap.name,
+          }
+        end
+        let(:old_tap) { CoreCaskTap.instance }
+        let(:default_tap) { CoreTap.instance }
+
+        before do
+          old_tap.path.mkpath
+          (old_tap.path/"tap_migrations.json").write tap_migrations.to_json
+          old_tap.clear_cache
+        end
+
+        it "does not warn when loading the short token" do
+          expect do
+            described_class.loader_for(token)
+          end.not_to output.to_stderr
+        end
+
+        it "does not warn when loading the full token in the default tap" do
+          expect do
+            described_class.loader_for("#{default_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(%r{Formula #{old_tap}/#{token} was renamed to #{token}\.}).to_stderr
+        end
+      end
+    end
+  end
 end