From 34ae9dc7f28d33120c27abd2bbbd341dd6044ce0 Mon Sep 17 00:00:00 2001
From: Enrico Forestieri <forenr@lyx.org>
Date: Sat, 5 Nov 2016 10:15:37 +0100
Subject: [PATCH] Avoid dataloss with \multicolumn

When \multicolumn{ncol}{align}{content} is parsed and the ncol
parameter is not a numeric value, this parameter is swallowed
and replaced with '1'. Hence, if the file is subsequently saved
a dataloss would occur. With this commit, \multicolumn is not
interpreted when ncol is not a numeric value and is left as is.

See also #10466
---
 src/mathed/MathParser.cpp | 51 +++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 23 deletions(-)

diff --git a/src/mathed/MathParser.cpp b/src/mathed/MathParser.cpp
index c0f3e87e60..4504a13a26 100644
--- a/src/mathed/MathParser.cpp
+++ b/src/mathed/MathParser.cpp
@@ -1364,35 +1364,40 @@ bool Parser::parse1(InsetMathGrid & grid, unsigned flags,
 		}
 
 		else if (t.cs() == "multicolumn") {
-			// extract column count and insert dummy cells
+			// if the columns are specified numerically,
+			// extract column count and insert dummy cells,
+			// otherwise parse it as an user macro
 			MathData count;
 			parse(count, FLAG_ITEM, mode);
-			int cols = 1;
-			if (!extractNumber(count, cols)) {
-				success_ = false;
-				error("can't extract number of multicolumn cells");
-			}
-			// resize the table if necessary
-			size_t first = grid.index(cellrow, cellcol);
-			for (int i = 1; i < cols; ++i) {
-				if (addCol(grid, cellcol)) {
-					size_t const idx = grid.index(cellrow, cellcol);
-					grid.cellinfo(idx).multi_ =
-						InsetMathGrid::CELL_PART_OF_MULTICOLUMN;
+			int cols;
+			if (extractNumber(count, cols)) {
+				// resize the table if necessary
+				size_t first = grid.index(cellrow, cellcol);
+				for (int i = 1; i < cols; ++i) {
+					if (addCol(grid, cellcol)) {
+						size_t const idx = grid.index(cellrow, cellcol);
+						grid.cellinfo(idx).multi_ =
+							InsetMathGrid::CELL_PART_OF_MULTICOLUMN;
+					}
 				}
-			}
 
-			// the first cell is the real thing, not a dummy
-			cell = &grid.cell(first);
-			grid.cellinfo(first).multi_ = InsetMathGrid::CELL_BEGIN_OF_MULTICOLUMN;
+				// the first cell is the real thing, not a dummy
+				cell = &grid.cell(first);
+				grid.cellinfo(first).multi_ =
+					InsetMathGrid::CELL_BEGIN_OF_MULTICOLUMN;
 
-			// read special alignment
-			MathData align;
-			parse(align, FLAG_ITEM, mode);
-			grid.cellinfo(first).align_ = asString(align);
+				// read special alignment
+				MathData align;
+				parse(align, FLAG_ITEM, mode);
+				grid.cellinfo(first).align_ = asString(align);
 
-			// parse the remaining contents into the "real" cell
-			parse(*cell, FLAG_ITEM, mode);
+				// parse the remaining contents into the "real" cell
+				parse(*cell, FLAG_ITEM, mode);
+			} else {
+				MathAtom at = MathAtom(new MathMacro(buf, t.cs()));
+				cell->push_back(at);
+				cell->push_back(MathAtom(new InsetMathBrace(count)));
+			}
 		}
 
 		else if (t.cs() == "limits" || t.cs() == "nolimits") {
-- 
2.39.2