Fix API::tap_from_source_download for relative paths.

Library/Homebrew/api.rb

@@ -175,6 +175,7 @@ module Homebrew
 
     sig { params(path: Pathname).returns(T.nilable(Tap)) }
     def self.tap_from_source_download(path)
+      path = path.expand_path
       source_relative_path = path.relative_path_from(Homebrew::API::HOMEBREW_CACHE_API_SOURCE)
       return if source_relative_path.to_s.start_with?("../")
 

Library/Homebrew/test/api_spec.rb

@@ -67,4 +67,31 @@ describe Homebrew::API do
       end.to raise_error(SystemExit)
     end
   end
+
+  describe "::tap_from_source_download" do
+    let(:api_cache_root) { Homebrew::API::HOMEBREW_CACHE_API_SOURCE }
+    let(:cache_path) do
+      api_cache_root/"Homebrew"/"homebrew-core"/"cf5c386c1fa2cb54279d78c0990dd7a0fa4bc327"/"Formula"/"foo.rb"
+    end
+
+    context "when given a path inside the API source cache" do
+      it "returns the corresponding tap" do
+        expect(described_class.tap_from_source_download(cache_path)).to eq CoreTap.instance
+      end
+    end
+
+    context "when given a path that is not inside the API source cache" do
+      let(:api_cache_root) { mktmpdir }
+
+      it "returns nil" do
+        expect(described_class.tap_from_source_download(cache_path)).to be_nil
+      end
+    end
+
+    context "when given a relative path that is not inside the API source cache" do
+      it "returns nil" do
+        expect(described_class.tap_from_source_download(Pathname("../foo.rb"))).to be_nil
+      end
+    end
+  end
 end