From 56a14c3fdeb54925b262e3db781bb95d888610ab Mon Sep 17 00:00:00 2001
From: Enrico Forestieri <forenr@lyx.org>
Date: Fri, 10 May 2019 08:09:26 +0200
Subject: [PATCH] Refined fix for #9633

A branch inset modifies the layout of the internal structures in
which the text is organized. When a branch is active, it is as if it
was not there, but its only presence makes a paragraph which would not
be the last one to actually be the last one, or the check for the
language of the previous paragraph to fail because there is no
previous paragraph before the first one in a branch inset.
Oney way I found to tackle it, is tracking whether the typesetted
paragraphs are actually part of an active branch inset and acting
accordingly.
---
 src/OutputParams.cpp       |  4 ++--
 src/OutputParams.h         |  5 +++++
 src/insets/InsetBranch.cpp |  7 +++++--
 src/output_latex.cpp       | 13 +++++++++++--
 4 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/src/OutputParams.cpp b/src/OutputParams.cpp
index 36816c2f7f..5efe7445eb 100644
--- a/src/OutputParams.cpp
+++ b/src/OutputParams.cpp
@@ -20,8 +20,8 @@ namespace lyx {
 
 OutputParams::OutputParams(Encoding const * enc)
 	: flavor(LATEX), math_flavor(NotApplicable), nice(false), is_child(false),
-	  moving_arg(false), intitle(false), inulemcmd(0), local_font(0), 
-	  master_language(0), encoding(enc), free_spacing(false),
+	  moving_arg(false), intitle(false), inbranch(false), inulemcmd(0),
+	  local_font(0),master_language(0), encoding(enc), free_spacing(false),
 	  use_babel(false), use_polyglossia(false), use_CJK(false),
 	  use_indices(false), use_japanese(false), linelen(0), depth(0),
 	  exportdata(new ExportData), postpone_fragile_stuff(false), inDisplayMath(false),
diff --git a/src/OutputParams.h b/src/OutputParams.h
index 52ab2925a5..3ec4eddf22 100644
--- a/src/OutputParams.h
+++ b/src/OutputParams.h
@@ -102,6 +102,11 @@ public:
 	*/
 	bool intitle;
 
+	/** inbranch == true means that the environment being typeset
+	    is inside an active branch inset.
+	*/
+	bool inbranch;
+
 	/** inulemcmd > 0 means that the environment in which the
 	    inset is typeset is part of a ulem or soul command (e.g., \uline,
 	    \uuline, \uwave, \sout or \xout). Insets that output latex commands
diff --git a/src/insets/InsetBranch.cpp b/src/insets/InsetBranch.cpp
index d30e348da5..88d00e641e 100644
--- a/src/insets/InsetBranch.cpp
+++ b/src/insets/InsetBranch.cpp
@@ -292,8 +292,11 @@ bool InsetBranch::producesOutput() const
 
 void InsetBranch::latex(otexstream & os, OutputParams const & runparams) const
 {
-	if (producesOutput())
-		InsetText::latex(os, runparams);
+	if (producesOutput()) {
+		OutputParams rp = runparams;
+		rp.inbranch = true;
+		InsetText::latex(os, rp);
+	}
 }
 
 
diff --git a/src/output_latex.cpp b/src/output_latex.cpp
index 60bc9f3d59..23e6d3f3fe 100644
--- a/src/output_latex.cpp
+++ b/src/output_latex.cpp
@@ -1194,7 +1194,7 @@ void TeXOnePar(Buffer const & buf,
 	if (localswitch_needed
 	    || (intitle_command && using_begin_end)
 	    || closing_rtl_ltr_environment
-	    || ((runparams.isLastPar || close_lang_switch)
+	    || (((runparams.isLastPar && !runparams.inbranch) || close_lang_switch)
 	        && (par_lang != outer_lang || (using_begin_end
 						&& style.isEnvironment()
 						&& par_lang != nextpar_lang)))) {
@@ -1610,14 +1610,23 @@ void latexParagraphs(Buffer const & buf,
 		state->open_encoding_ = none;
 	}
 	// Likewise for polyglossia or when using begin/end commands
+	// or after an active branch inset with a language switch
+	Language const * const outer_language = (runparams.local_font != 0)
+			? runparams.local_font->language() : bparams.language;
+	string const & prev_lang = runparams.use_polyglossia
+			? getPolyglossiaEnvName(outer_language)
+			: outer_language->babel();
 	string const & cur_lang = openLanguageName(state);
-	if (maintext && !is_child && !cur_lang.empty()) {
+	if (((runparams.inbranch && langOpenedAtThisLevel(state) && prev_lang != cur_lang)
+	     || (maintext && !is_child)) && !cur_lang.empty()) {
 		os << from_utf8(subst(lang_end_command,
 					"$$lang",
 					cur_lang))
 		   << '\n';
 		if (using_begin_end)
 			popLanguageName();
+	} else if (runparams.inbranch && !using_begin_end && prev_lang != cur_lang) {
+		os << subst(lang_begin_command, "$$lang", prev_lang) << '\n';
 	}
 
 	// reset inherited encoding