Fix showing range diff across a rename when filtering by path

We need to pass the union of filter paths at both ends of the range.

pkg/gui/controllers/helpers/diff_helper.go

@@ -57,8 +57,20 @@ func (self *DiffHelper) GetUpdateTaskForRenderingCommitsDiff(commit *models.Comm
 		from, to := refRange.From, refRange.To
 		args := []string{from.ParentRefName(), to.RefName(), "--stat", "-p"}
 		args = append(args, "--")
-		if path := self.c.Modes().Filtering.GetPath(); path != "" {
+		if filterPath := self.c.Modes().Filtering.GetPath(); filterPath != "" {
-			args = append(args, path)
+			// If both refs are commits, filter by the union of their paths. This is useful for
+			// example when diffing a range of commits in filter-by-path mode across a rename.
+			fromCommit, ok1 := from.(*models.Commit)
+			toCommit, ok2 := to.(*models.Commit)
+			if ok1 && ok2 {
+				paths := append(self.FilterPathsForCommit(fromCommit), self.FilterPathsForCommit(toCommit)...)
+				args = append(args, lo.Uniq(paths)...)
+			} else {
+				// If either ref is not a commit (which is possible in sticky diff mode, when
+				// diffing against a branch or tag), we just filter by the filter path; that's the
+				// best we can do in this case.
+				args = append(args, filterPath)
+			}
 		}
 		cmdObj := self.c.Git().Diff.DiffCmdObj(args)
 		prefix := style.FgYellow.Sprintf("%s %s-%s\n\n", self.c.Tr.ShowingDiffForRange, from.ShortRefName(), to.ShortRefName())

pkg/integration/tests/filter_by_path/show_diffs_for_renamed_file.go

@@ -113,7 +113,6 @@ var ShowDiffsForRenamedFile = NewIntegrationTest(NewIntegrationTestArgs{
 			Press(keys.Universal.RangeSelectUp)
 
 		t.Views().Main().ContainsLines(
-			/* EXPECTED:
 			Contains("Showing diff for range"),
 			Equals(""),
 			Equals(" oldFile => newFile | 2 +-"),
@@ -131,19 +130,6 @@ var ShowDiffsForRenamedFile = NewIntegrationTest(NewIntegrationTestArgs{
 			Equals("+y"),
 			Equals(" b"),
 			Equals(" c"),
-			ACTUAL: */
-			Equals(" newFile | 3 +++"),
-			Equals(" 1 file changed, 3 insertions(+)"),
-			Equals(""),
-			Equals("diff --git a/newFile b/newFile"),
-			Equals("new file mode 100644"),
-			Contains("index"),
-			Equals("--- /dev/null"),
-			Equals("+++ b/newFile"),
-			Equals("@@ -0,0 +1,3 @@"),
-			Equals("+y"),
-			Equals("+b"),
-			Equals("+c"),
 		)
 	},
 })