From f214ba90cc631889dffdf31fccc579379605e251 Mon Sep 17 00:00:00 2001
From: Stefan Haller <stefan@haller-berlin.de>
Date: Tue, 1 Sep 2026 19:01:23 +0200
Subject: [PATCH] Ask a parsed patch which of its lines a selection covers

Staging a selection walks the file's diff to find the lines the user
pointed at, by where each of them sits in the file. The next commit needs
the same answer for a single row, so pull the walk out of the staging path
before there are two copies of it.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 .../controllers/working_tree_diff_actions.go  | 65 +++++++++++--------
 1 file changed, 37 insertions(+), 28 deletions(-)

diff --git a/pkg/gui/controllers/working_tree_diff_actions.go b/pkg/gui/controllers/working_tree_diff_actions.go
index 75b5f97fc..233ecec13 100644
--- a/pkg/gui/controllers/working_tree_diff_actions.go
+++ b/pkg/gui/controllers/working_tree_diff_actions.go
@@ -198,34 +198,7 @@ func (self *WorkingTreeDiffActions) applyDiffLines(
 ) (bool, error) {
 	parsedPatch := patch.Parse(self.c.Git().WorkingTree.WorktreeFileDiff(file, git_commands.DiffModePlain, sourceCached))
 
-	type changeLine struct {
-		lineNumber int
-		isDeletion bool
-	}
-	selected := set.New[changeLine]()
-	for _, info := range infos {
-		if info.Type == types.DiffLineDeleted {
-			selected.Add(changeLine{info.OldLine, true})
-		} else {
-			selected.Add(changeLine{info.NewLine, false})
-		}
-	}
-
-	var patchLineIndices []int
-	for idx, line := range parsedPatch.Lines() {
-		var key changeLine
-		switch {
-		case line.IsAddition():
-			key = changeLine{parsedPatch.LineNumberOfLine(idx), false}
-		case line.IsDeletion():
-			key = changeLine{parsedPatch.OldLineNumberOfLine(idx), true}
-		default:
-			continue
-		}
-		if selected.Includes(key) {
-			patchLineIndices = append(patchLineIndices, idx)
-		}
-	}
+	patchLineIndices := changeLineIndices(parsedPatch, infos)
 
 	changesLeft := len(patchLineIndices) < changeLineCount(parsedPatch)
 
@@ -256,6 +229,42 @@ func (self *WorkingTreeDiffActions) applyDiffLines(
 	return changesLeft, self.c.Git().Patch.ApplyPatch(patchToApply, opts)
 }
 
+// changeLineIndices says which lines of a parsed patch the given diff rows are, as the
+// indices a patch is built in terms of. Each row is looked for by where it sits in the
+// file: an addition by its place in the new version, a deletion by its place in the
+// old one, which is what tells the two halves of a changed line apart.
+func changeLineIndices(parsedPatch *patch.Patch, infos []types.DiffLineInfo) []int {
+	type changeLine struct {
+		lineNumber int
+		isDeletion bool
+	}
+	selected := set.New[changeLine]()
+	for _, info := range infos {
+		if info.Type == types.DiffLineDeleted {
+			selected.Add(changeLine{info.OldLine, true})
+		} else {
+			selected.Add(changeLine{info.NewLine, false})
+		}
+	}
+
+	var indices []int
+	for idx, line := range parsedPatch.Lines() {
+		var key changeLine
+		switch {
+		case line.IsAddition():
+			key = changeLine{parsedPatch.LineNumberOfLine(idx), false}
+		case line.IsDeletion():
+			key = changeLine{parsedPatch.OldLineNumberOfLine(idx), true}
+		default:
+			continue
+		}
+		if selected.Includes(key) {
+			indices = append(indices, idx)
+		}
+	}
+	return indices
+}
+
 // changeLineCount returns how many of a patch's lines are changes rather than context
 // or header. A selection of the whole diff covers exactly that many.
 func changeLineCount(p *patch.Patch) int {