tdf#76683 writerfilter: TwipMeasure must be positive

...and the column width must not be negative.

The previous column logic ensured that the total width was
larger than the reference by adding a fake buffer
and then subtracted the difference from the final column.
In the case of a zero-width final column, it could become negative.
The current logic ensures that the total width is less than
the reference width, and then adds the difference
(which should be a smaller difference now) to the final column.

Regression potential - early columns that need every single twip
of bonus space might not fit anymore. On the other hand,
ending columns might be fixed...

Change-Id: Ie75d455e8ed62dbec5a1b9c901417df8d842ace8
Reviewed-on: https://gerrit.libreoffice.org/59400
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/sw/qa/extras/ooxmlexport/data/tdf76683_negativeTwipsMeasure.docx b/sw/qa/extras/ooxmlexport/data/tdf76683_negativeTwipsMeasure.docx
new file mode 100644
index 000000000000..eb769fdcc3bf
--- /dev/null
+++ b/sw/qa/extras/ooxmlexport/data/tdf76683_negativeTwipsMeasure.docx
diff --git a/sw/qa/extras/ooxmlexport/ooxmlexport11.cxx b/sw/qa/extras/ooxmlexport/ooxmlexport11.cxx
index db52d019439b..adb0dc6f4264 100644
--- a/sw/qa/extras/ooxmlexport/ooxmlexport11.cxx
+++ b/sw/qa/extras/ooxmlexport/ooxmlexport11.cxx
@@ -160,6 +160,17 @@ DECLARE_OOXMLEXPORT_TEST(testTdf82065_Ind_start_strict, "tdf82065_Ind_start_stri
     CPPUNIT_ASSERT_EQUAL_MESSAGE("IndentAt defined", true, bFoundIndentAt);
 }
 
+DECLARE_OOXMLEXPORT_TEST(testTdf76683_negativeTwipsMeasure, "tdf76683_negativeTwipsMeasure.docx")
+{
+    xmlDocPtr pXmlDoc = parseExport("word/document.xml");
+    if (!pXmlDoc)
+        return;
+    assertXPath(pXmlDoc, "/w:document/w:body/w:sectPr/w:cols/w:col", 2);
+    sal_uInt32 nColumn1 = getXPath(pXmlDoc, "/w:document/w:body/w:sectPr/w:cols/w:col[1]", "w").toUInt32();
+    sal_uInt32 nColumn2 = getXPath(pXmlDoc, "/w:document/w:body/w:sectPr/w:cols/w:col[2]", "w").toUInt32();
+    CPPUNIT_ASSERT( nColumn1 > nColumn2 );
+}
+
 DECLARE_OOXMLEXPORT_TEST(testTdf112694, "tdf112694.docx")
 {
     uno::Any aPageStyle = getStyles("PageStyles")->getByName("Standard");