From 31471496fd53b20b684173da56ba59d0da7f90fc Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Tue, 19 Jan 2016 12:02:43 +0100
Subject: [PATCH] Allow breaking a row element at a leading/trailing space

When an inset is separated from the adjacent string by a space, it is
reasonable to be able to break the string after the space.
Unfortunately, QTextLayout does not do that.

This patch reverts the workaround inserted in 71378268 and replaces it
with a different trick: the string is enlosed between a pair of
zero-width non breaking space characters, so that the leading/trailing
spaces are now normal spaces, where QTextLayout will agree to break
the string.

    Fixes bug #9921 for good.
---
 src/Row.cpp                          | 11 -----------
 src/frontends/qt4/GuiFontMetrics.cpp | 14 ++++++++++++--
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/src/Row.cpp b/src/Row.cpp
index 2bfe55a1b8..6e51fb192b 100644
--- a/src/Row.cpp
+++ b/src/Row.cpp
@@ -129,17 +129,6 @@ bool Row::Element::breakAt(int w, bool force)
 		return true;
 	}
 
-	// Qt will not break at a leading space, and we need that sometimes, see
-	//   http://www.lyx.org/trac/ticket/9921.
-	// It would be nice to fix this properly, but for now do it by hand.
-	// FIXME: figure out what to do for RtL text.
-	if (!isRTL() && !str.empty() && str[0] == ' ') {
-		dim.wid = 0;
-		str = ' ';
-		endpos = pos + 1;
-		return true;
-	}
-
 	return false;
 }
 
diff --git a/src/frontends/qt4/GuiFontMetrics.cpp b/src/frontends/qt4/GuiFontMetrics.cpp
index c58be2aee3..fdb8c73bc6 100644
--- a/src/frontends/qt4/GuiFontMetrics.cpp
+++ b/src/frontends/qt4/GuiFontMetrics.cpp
@@ -219,7 +219,16 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool const rtl, bool const
 	if (s.empty())
 		return false;
 	QTextLayout tl;
-	tl.setText(toqstr(s));
+	/* Qt will not break at a leading or trailing space, and we need
+	 * that sometimes, see http://www.lyx.org/trac/ticket/9921.
+	 *
+	 * To work around the problem, we enclose the string between
+	 * zero-width characters so that the QTextLayout algorithm will
+	 * agree to break the text at these extremal spaces.
+	*/
+	// Unicode character ZERO WIDTH NO-BREAK SPACE
+	QChar const zerow_nbsp(0xfeff);
+	tl.setText(zerow_nbsp + toqstr(s) + zerow_nbsp);
 	tl.setFont(font_);
 	// Note that both setFlags and the enums are undocumented
 	tl.setFlags(rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight);
@@ -234,7 +243,8 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool const rtl, bool const
 	if (int(line.naturalTextWidth()) > x)
 		return false;
 	x = int(line.naturalTextWidth());
-	s = s.substr(0, line.textLength());
+	// The -1 is here to account for the leading zerow_nbsp.
+	s = s.substr(0, line.textLength() - 1);
 	return true;
 }