Merge pull request #23428 from Homebrew/symlink-target-check

Skip cask link when symlink already correct

Library/Homebrew/cask/artifact/symlinked.rb

@@ -79,6 +79,9 @@ module Cask
              (target.realpath == source.realpath || target.realpath.to_s.start_with?("#{cask.caskroom_path}/"))
             opoo "#{message}; overwriting."
             Utils.gain_permissions_remove(target, command:)
+          elsif target_links_to_source?
+            ohai "#{self.class.english_name} '#{source.basename}' is already linked to '#{target}'"
+            return
           elsif (formula = conflicting_formula)
             opoo "#{message} from formula #{formula}; skipping link."
             return
@@ -113,6 +116,14 @@ module Cask
                                 sudo: !target.dirname.writable?
       end
 
+      sig { returns(T::Boolean) }
+      def target_links_to_source?
+        target.symlink? && target.realpath == source.realpath
+      rescue => e
+        odebug "Error checking whether #{target} links to #{source}: #{e}"
+        false
+      end
+
       # Check if the target file is a symlink that originates from a formula
       # with the same name as this cask, indicating a potential conflict
       sig { returns(T.nilable(String)) }

Library/Homebrew/test/cask/artifact/binary_spec.rb

@@ -86,6 +86,27 @@ RSpec.describe Cask::Artifact::Binary, :cask do
     expect(File.readlink(expected_path)).to eq("/tmp")
   end
 
+  it "skips linking when the target is already a symlink to the source" do
+    artifact = artifacts.first
+    expected_path.make_symlink(artifact.source)
+
+    expect do
+      artifact.install_phase(command: NeverSudoSystemCommand, force: false)
+    end.to output(/is already linked/).to_stdout
+
+    expect(expected_path.readlink).to eq(artifact.source)
+  end
+
+  it "raises a clean error when the target symlink cannot be resolved" do
+    artifact = artifacts.first
+    expected_path.make_symlink(artifact.source)
+    allow(artifact.target).to receive(:realpath).and_raise(Errno::EACCES)
+
+    expect do
+      artifact.install_phase(command: NeverSudoSystemCommand, force: false)
+    end.to raise_error(Cask::CaskError, /already a Binary/)
+  end
+
   it "creates parent directory if it doesn't exist" do
     FileUtils.rmdir binarydir