Move where a jump lands into the diff line helper

Where a focus or a click puts the focused main view's selection is
worked out in the diff line helper; where a jump puts it is worked out
on the main view controller, though it is the same question about the
same pane. A jump asked for from anywhere else — from a panel below the
pane, or from a click on a link in the diff — has no way to reach that
answer.

Move it over. The controller keeps placeNavigationTarget as the short
way to say it for the jumps it makes itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/gui/controllers/helpers/diff_line_selection.go

@@ -7,9 +7,9 @@ import (
 	"github.com/samber/lo"
 )
 
-// Putting a selection in the focused main view: where it starts out, and how it is
-// widened to a whole change block. Both are answered from what the view is showing,
-// as recovered by the queries next door.
+// Putting a selection in the focused main view: where it starts out, where a jump
+// leaves it, and how it is widened to a whole change block. All three are answered
+// from what the view is showing, as recovered by the queries next door.
 
 // EstablishSelection turns on the focused main view's selection once the view has
 // been focused. clickedViewLine is the view line a click pointed at, or -1 for
@@ -63,6 +63,66 @@ func (self *DiffLineHelper) EstablishSelection(mainContext *context.MainContext,
 	self.ShowSelectionAtLine(view, target, false)
 }
 
+// PlaceNavigationTarget moves the pane's selection to the row a jump found, bringing
+// it on screen if it isn't already. With no selection to move — a pane that isn't
+// focused, or one showing a diff with nothing selectable in it — the row goes to the
+// top of the view instead, that being all a jump can do there.
+//
+// alignTop asks for the target to become the view's top line, so that everything that
+// begins there is on screen. It only applies to a target the view has to scroll to: a
+// jump to something already on screen leaves the view alone, there being nothing to
+// gain from moving what the user is looking at. In hunk mode what ends up selected is
+// the first change block at or below the target, which a large context size can put
+// further down than a screenful; the selection is then scrolled into view as any other
+// jump's is, and the alignment gives way to that.
+func (self *DiffLineHelper) PlaceNavigationTarget(
+	pane types.DiffPaneContext, target int, alignTop bool,
+) {
+	view := pane.GetView()
+	if !view.Highlight {
+		view.SetOrigin(0, target)
+		return
+	}
+	if alignTop {
+		self.scrollTargetToTop(pane, target)
+	}
+	// Jumping to another block or file moves the cursor without shift held, so a
+	// range that grows only while shift is held collapses rather than stretching all
+	// the way to the target. A sticky range stretches instead; this is the point of
+	// being sticky.
+	self.CollapseNonStickyRange(pane)
+	if pane.DiffSelectState().Mode == types.DiffSelectModeHunk {
+		self.SelectChangeBlock(pane, target, true)
+		return
+	}
+	// Line mode leaves a single-line selection at the target; an active range extends
+	// to it, the anchor being untouched.
+	self.ShowSelectionAtLine(view, target, true)
+}
+
+// scrollTargetToTop scrolls the given row of the diff to the top of the view, leaving
+// the view where it is when that row is on screen already. The last screenful of the
+// diff is as far as it goes, so that the view doesn't scroll past the end of what it is
+// showing.
+func (self *DiffLineHelper) scrollTargetToTop(pane types.DiffPaneContext, target int) {
+	view := pane.GetView()
+	originY, height := pane.GetViewTrait().ViewPortYBounds()
+	if target >= originY && target < originY+height {
+		return
+	}
+	view.SetOriginY(min(target, max(0, view.ViewLinesHeight()-height)))
+}
+
+// CollapseNonStickyRange drops a range that only grows while shift is held back to a
+// single line at the cursor.
+func (self *DiffLineHelper) CollapseNonStickyRange(pane types.DiffPaneContext) {
+	sel := pane.DiffSelectState()
+	if sel.Mode == types.DiffSelectModeRange && !sel.RangeIsSticky {
+		sel.Mode = types.DiffSelectModeLine
+		pane.GetView().CancelRangeSelect()
+	}
+}
+
 // changeToSelectOnScreen returns the change line keyboard focus establishes the
 // selection on. In hunk mode that is the first block that begins on screen, so that
 // the block being offered up is one the user can see the extent of, falling back to a

pkg/gui/controllers/main_view_controller.go

@@ -842,50 +842,8 @@ func (self *MainViewController) prevFile() error {
 	return nil
 }
 
-// placeNavigationTarget moves the selection to the row a jump found, bringing it on
-// screen if it isn't already.
-//
-// alignTop asks for the target to become the view's top line, so that everything that
-// begins there is on screen. It only applies to a target the view has to scroll to: a
-// jump to something already on screen leaves the view alone, there being nothing to
-// gain from moving what the user is looking at. In hunk mode what ends up selected is
-// the first change block at or below the target, which a large context size can put
-// further down than a screenful; the selection is then scrolled into view as any other
-// jump's is, and the alignment gives way to that.
 func (self *MainViewController) placeNavigationTarget(target int, alignTop bool) {
-	v := self.context.GetView()
-	if !v.Highlight {
-		v.SetOrigin(0, target)
-		return
-	}
-	if alignTop {
-		self.scrollTargetToTop(target)
-	}
-	// Jumping to another block or file moves the cursor without shift held, so a
-	// range that grows only while shift is held collapses rather than stretching all
-	// the way to the target. A sticky range stretches instead; this is the point of
-	// being sticky.
-	self.collapseNonStickyRange()
-	if self.diffSelectState().Mode == types.DiffSelectModeHunk {
-		self.selectHunkAround(target, true)
-		return
-	}
-	// Line mode leaves a single-line selection at the target; an active range extends
-	// to it, the anchor being untouched.
-	self.c.Helpers().DiffLine.ShowSelectionAtLine(v, target, true)
-}
-
-// scrollTargetToTop scrolls the given row of the diff to the top of the view, leaving
-// the view where it is when that row is on screen already. The last screenful of the
-// diff is as far as it goes, so that the view doesn't scroll past the end of what it is
-// showing.
-func (self *MainViewController) scrollTargetToTop(target int) {
-	view := self.context.GetView()
-	originY, height := self.context.GetViewTrait().ViewPortYBounds()
-	if target >= originY && target < originY+height {
-		return
-	}
-	view.SetOriginY(min(target, max(0, view.ViewLinesHeight()-height)))
+	self.c.Helpers().DiffLine.PlaceNavigationTarget(self.context, target, alignTop)
 }
 
 // moveCursor moves the selection cursor by delta view lines (negative = up), with the
@@ -917,17 +875,7 @@ func (self *MainViewController) collapseForLineMove() {
 		self.context.GetView().CancelRangeSelect()
 		return
 	}
-	self.collapseNonStickyRange()
-}
-
-// collapseNonStickyRange drops a range that only grows while shift is held back to a
-// single line at the cursor.
-func (self *MainViewController) collapseNonStickyRange() {
-	sel := self.diffSelectState()
-	if sel.Mode == types.DiffSelectModeRange && !sel.RangeIsSticky {
-		sel.Mode = types.DiffSelectModeLine
-		self.context.GetView().CancelRangeSelect()
-	}
+	self.c.Helpers().DiffLine.CollapseNonStickyRange(self.context)
 }
 
 // adjustSelection moves the selection by delta view lines, for the plain up/down and