Allow cherry-picking merge commits

Now that we use git cherry-pick to implement it, there's no reason not to.

Author: stefanhaller

Diff for: pkg/gui/controllers/basic_commits_controller.go

@@ -366,10 +366,6 @@ func (self *BasicCommitsController) canCopyCommits(selectedCommits []*models.Com
 		if commit.Hash == "" {
 			return &types.DisabledReason{Text: self.c.Tr.CannotCherryPickNonCommit, ShowErrorInPanel: true}
 		}
-
-		if commit.IsMerge() {
-			return &types.DisabledReason{Text: self.c.Tr.CannotCherryPickMergeCommit, ShowErrorInPanel: true}
-		}
 	}
 
 	return nil

Diff for: pkg/integration/tests/cherry_pick/cherry_pick_merge.go

@@ -0,0 +1,80 @@
+package cherry_pick
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CherryPickMerge = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Cherry pick a merge commit",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.
+			EmptyCommit("base").
+			NewBranch("first-branch").
+			NewBranch("second-branch").
+			Checkout("first-branch").
+			Checkout("second-branch").
+			CreateFileAndAdd("file1.txt", "content").
+			Commit("one").
+			CreateFileAndAdd("file2.txt", "content").
+			Commit("two").
+			Checkout("master").
+			Merge("second-branch").
+			Checkout("first-branch")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Branches().
+			Focus().
+			Lines(
+				Contains("first-branch"),
+				Contains("master"),
+				Contains("second-branch"),
+			).
+			SelectNextItem().
+			PressEnter()
+
+		t.Views().SubCommits().
+			IsFocused().
+			Lines(
+				Contains("⏣─╮ Merge branch 'second-branch'").IsSelected(),
+				Contains("│ ◯ two"),
+				Contains("│ ◯ one"),
+				Contains("◯ ╯ base"),
+			).
+			// copy the merge commit
+			Press(keys.Commits.CherryPickCopy)
+
+		t.Views().Information().Content(Contains("1 commit copied"))
+
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("base").IsSelected(),
+			).
+			Press(keys.Commits.PasteCommits).
+			Tap(func() {
+				t.ExpectPopup().Alert().
+					Title(Equals("Cherry-pick")).
+					Content(Contains("Are you sure you want to cherry-pick the 1 copied commit(s) onto this branch?")).
+					Confirm()
+			}).
+			Tap(func() {
+				t.Views().Information().Content(DoesNotContain("commit copied"))
+			}).
+			Lines(
+				Contains("Merge branch 'second-branch'").IsSelected(),
+				Contains("base"),
+			)
+
+		t.Views().Main().ContainsLines(
+			Contains("Merge branch 'second-branch'"),
+			Contains("---"),
+			Contains("file1.txt | 1 +"),
+			Contains("file2.txt | 1 +"),
+			Contains("2 files changed, 2 insertions(+)"),
+		)
+	},
+})

Diff for: pkg/integration/tests/test_list.go

@@ -82,6 +82,7 @@ var tests = []*components.IntegrationTest{
 	cherry_pick.CherryPick,
 	cherry_pick.CherryPickConflicts,
 	cherry_pick.CherryPickDuringRebase,
+	cherry_pick.CherryPickMerge,
 	cherry_pick.CherryPickRange,
 	commit.AddCoAuthor,
 	commit.AddCoAuthorRange,