[LyX/master] Fix assertion in caret display code

[Jean-Marc Lasgouttes]

commit e6b54ea4d2e28d55565699ded45da971278b23bf
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Sun Jul 14 23:20:29 2019 +0200

    Fix assertion in caret display code
    
    It is not a good idea to call caretPosAndHeight when the caret is in a
    paragraph that is not in cached metrics. This can happen when not
    using "cursor follows scrollbar".
    
    This commit refactor things a bit so that testing is done in
    BufferView.
    
    This bug is not in 2.3.x.
---
 src/BufferView.cpp                |   11 ++++++++---
 src/BufferView.h                  |    4 ++--
 src/frontends/qt4/GuiWorkArea.cpp |   15 +++++----------
 3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/src/BufferView.cpp b/src/BufferView.cpp
index 2068f05..97adab8 100644
--- a/src/BufferView.cpp
+++ b/src/BufferView.cpp
@@ -3044,11 +3044,16 @@ void BufferView::caretPosAndHeight(Point & p, int & h) 
const
 }
 
 
-bool BufferView::cursorInView(Point const & p, int h) const
+bool BufferView::caretInView() const
 {
-       Cursor const & cur = cursor();
+       if (!paragraphVisible(cursor()))
+               return false;
+       Point p;
+       int h;
+       caretPosAndHeight(p, h);
+
        // does the cursor touch the screen ?
-       if (p.y_ + h < 0 || p.y_ >= workHeight() || !paragraphVisible(cur))
+       if (p.y_ + h < 0 || p.y_ >= workHeight())
                return false;
        return true;
 }
diff --git a/src/BufferView.h b/src/BufferView.h
index 45928f2..40dd0d2 100644
--- a/src/BufferView.h
+++ b/src/BufferView.h
@@ -307,8 +307,8 @@ public:
        Point getPos(DocIterator const & dit) const;
        /// is the paragraph of the cursor visible ?
        bool paragraphVisible(DocIterator const & dit) const;
-       /// is the cursor currently visible in the view
-       bool cursorInView(Point const & p, int h) const;
+       /// is the caret currently visible in the view
+       bool caretInView() const;
        /// get the position and height of the caret
        void caretPosAndHeight(Point & p, int & h) const;
 
diff --git a/src/frontends/qt4/GuiWorkArea.cpp 
b/src/frontends/qt4/GuiWorkArea.cpp
index 02c56c2..6a7c995 100644
--- a/src/frontends/qt4/GuiWorkArea.cpp
+++ b/src/frontends/qt4/GuiWorkArea.cpp
@@ -439,11 +439,8 @@ void GuiWorkArea::startBlinkingCaret()
        if (view().busy())
                return;
 
-       Point p;
-       int h = 0;
-       d->buffer_view_->caretPosAndHeight(p, h);
        // Don't start blinking if the cursor isn't on screen.
-       if (!d->buffer_view_->cursorInView(p, h))
+       if (!d->buffer_view_->caretInView())
                return;
 
        d->showCaret();
@@ -583,10 +580,7 @@ void GuiWorkArea::Private::resizeBufferView()
        // Warn our container (GuiView).
        p->busy(true);
 
-       Point point;
-       int h = 0;
-       buffer_view_->caretPosAndHeight(point, h);
-       bool const caret_in_view = buffer_view_->cursorInView(point, h);
+       bool const caret_in_view = buffer_view_->caretInView();
        buffer_view_->resize(p->viewport()->width(), p->viewport()->height());
        if (caret_in_view)
                buffer_view_->scrollToCursor();
@@ -610,11 +604,12 @@ void GuiWorkArea::Private::resizeBufferView()
 
 void GuiWorkArea::Private::updateCaretGeometry()
 {
+       if (!buffer_view_->caretInView())
+               return;
+
        Point point;
        int h = 0;
        buffer_view_->caretPosAndHeight(point, h);
-       if (!buffer_view_->cursorInView(point, h))
-               return;
 
        // RTL or not RTL
        bool l_shape = false;