[LyX/master] Correctly protect macros with optionals inserted in an optional argument

[Enrico Forestieri]

commit 2731c5dc5511fce18cadaec76663d8dfdaa65d10
Author: Enrico Forestieri <for...@lyx.org>
Date:   Fri Apr 26 15:30:08 2019 +0200

    Correctly protect macros with optionals inserted in an optional argument
    
    The trick turns out to be inserting in braces the whole optional
    argument, rather than the single macro.
    
    See #11552 for the long history.
---
 src/mathed/InsetMathMacro.cpp |   20 +++++++++++++++-----
 1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/mathed/InsetMathMacro.cpp b/src/mathed/InsetMathMacro.cpp
index 4b5242e..5269df0 100644
--- a/src/mathed/InsetMathMacro.cpp
+++ b/src/mathed/InsetMathMacro.cpp
@@ -1101,14 +1101,24 @@ void InsetMathMacro::write(WriteStream & os) const
                // For correctly parsing it when a document is reloaded, we
                // need to enclose an optional argument in braces if it starts
                // with a script inset with empty nucleus or ends with a
-               // delimiter-size-modifier macro (see #10497 and #11346)
+               // delimiter-size-modifier macro (see #10497 and #11346).
+               // We also need to do that when the optional argument
+               // contains macros with optionals.
                bool braced = false;
                size_type last = cell(i).size() - 1;
-               if (cell(i).size() && 
cell(i)[last].nucleus()->asUnknownInset()) {
-                       latexkeys const * l = 
in_word_set(cell(i)[last].nucleus()->name());
+               if (cell(i).size() && cell(i)[last]->asUnknownInset()) {
+                       latexkeys const * l = 
in_word_set(cell(i)[last]->name());
                        braced = (l && l->inset == "big");
-               } else if (cell(i).size() && 
cell(i)[0].nucleus()->asScriptInset()) {
-                       braced = 
cell(i)[0].nucleus()->asScriptInset()->nuc().empty();
+               } else if (cell(i).size() && cell(i)[0]->asScriptInset()) {
+                       braced = cell(i)[0]->asScriptInset()->nuc().empty();
+               } else {
+                       for (size_type j = 0; j < cell(i).size(); ++j) {
+                               InsetMathMacro const * ma = 
cell(i)[j]->asMacro();
+                               if (ma && ma->optionals()) {
+                                       braced = true;
+                                       break;
+                               }
+                       }
                }
                if (braced)
                        os << "[{" << cell(i) << "}]";