From aadf3d8a5da69a5a0a21f4f4420407ce0da37691 Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Mon, 1 Jul 2024 23:56:33 +0200
Subject: [PATCH] Make BufferView::singeParUpdate more robust

In some cases, it might happen that this method is called with no
metrics or position known for the current paragraph.

Take care of these cases to avoid assertions.

Remove setting of inset positions in the method, but make sure that
updateMetrics(false) is always called to get everything right.

In the new code, updateMetrics(bool) is the method that sets
everything right with minimal effort.

(cherry picked from commit 89ab9eb569ec0eea87d9a8c269eb87507934e1c5)
---
 src/BufferView.cpp | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/BufferView.cpp b/src/BufferView.cpp
index 428c03299f..1fdfa78e2a 100644
--- a/src/BufferView.cpp
+++ b/src/BufferView.cpp
@@ -564,10 +564,12 @@ void BufferView::processUpdateFlags(Update::flags flags)
 	// are not already redrawing all).
 	// We handle this before FitCursor because the later will require
 	// correct metrics at cursor position.
-	if (!(flags & Update::ForceDraw)
-			&& (flags & Update::SinglePar)
-			&& !singleParUpdate())
-		updateMetrics(true);
+	if (!(flags & Update::ForceDraw) && (flags & Update::SinglePar)) {
+		if (singleParUpdate())
+			updateMetrics(false);
+		else
+			updateMetrics(true);
+	}
 
 	// Then make sure that the screen contains the cursor if needed
 	if (flags & Update::FitCursor) {
@@ -3132,6 +3134,10 @@ bool BufferView::singleParUpdate()
 	if (d->inlineCompletionPos_.fixIfBroken())
 		d->inlineCompletionPos_ = DocIterator();
 
+	if (!tm.contains(pit)) {
+		LYXERR(Debug::PAINTING, "SinglePar optimization failed: no known metrics");
+		return false;
+	}
 	/* Try to rebreak only the paragraph containing the cursor (if
 	 * this paragraph contains insets etc., rebreaking will
 	 * recursively descend). We need a full redraw if either
@@ -3149,18 +3155,19 @@ bool BufferView::singleParUpdate()
 	tm.redoParagraph(pit);
 	ParagraphMetrics & pm = tm.parMetrics(pit);
 	if (pm.height() != old_dim.height()
-		|| (pm.width() != old_dim.width() && old_dim.width() == tm.width())) {
+	     || (pm.width() != old_dim.width() && old_dim.width() == tm.width())) {
 		// Paragraph height or width has changed so we cannot proceed
 		// to the singlePar optimisation.
-		LYXERR(Debug::PAINTING, "SinglePar optimization failed.");
+		LYXERR(Debug::PAINTING, "SinglePar optimization failed: paragraph metrics changed");
 		return false;
 	}
 	// Since position() points to the baseline of the first row, we
 	// may have to update it. See ticket #11601 for an example where
 	// the height does not change but the ascent does.
-	pm.setPosition(pm.position() - old_dim.ascent() + pm.ascent());
-
-	tm.updatePosCache(pit);
+	if (pm.hasPosition())
+		pm.setPosition(pm.position() - old_dim.ascent() + pm.ascent());
+	else
+		LYXERR0("SinglePar optimization succeeded, but no position to update");
 
 	LYXERR(Debug::PAINTING, "\ny1: " << pm.top() << " y2: " << pm.bottom()
 		<< " pit: " << pit << " singlepar: 1");