sc ooxml: don't write empty dxf border sides

A dxf holds only incremental formatting that is layered on top of an
object's existing format. So an absent border side is left as-is, while
an empty side element (e.g. <left/>) defaults to style="none" and clears
that border. Writing every side unconditionally made a headerRow that
only defines a bottom border also clear the left/right/top borders it
should inherit from the wholeTable element (based on ooxml standard).
(only visible after re-importing into Excel)

Change-Id: Idb703badb7649f7f91d57324295b39f68ec234c1
Signed-off-by: Balazs Varga <balazs.varga@collabora.com>
Reviewed-on: https://gerrit.collaboraoffice.com/c/online/+/5591
Tested-by: Jenkins CPCI <releng@collaboraoffice.com>
Reviewed-by: Tomaž Vajngerl <tomaz.vajngerl@collabora.com>
(cherry picked from commit cc0181aec07f66847b9c5a06cd047d50abc5a70c)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/207623
Tested-by: Jenkins
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>

sc/qa/unit/subsequent_export_test6.cxx

@@ -224,6 +224,20 @@ CPPUNIT_TEST_FIXTURE(ScExportTest6, testTableStyleInnerBordersExportXLSX)
     assertXPath(pStyles, sBorder + "/x:vertical/x:color", "theme", u"8");
     assertXPath(pStyles, sBorder + "/x:horizontal", "style", u"thin");
     assertXPath(pStyles, sBorder + "/x:horizontal/x:color", "theme", u"8");
+
+    sal_Int32 nHeaderRowDxfId
+        = getXPath(
+              pStyles,
+              "/x:styleSheet/x:tableStyles/x:tableStyle/x:tableStyleElement[@type='headerRow']",
+              "dxfId")
+              .toInt32();
+    CPPUNIT_ASSERT(nHeaderRowDxfId >= 0);
+    OString sHdrBorder
+        = "/x:styleSheet/x:dxfs/x:dxf[" + OString::number(nHeaderRowDxfId + 1) + "]/x:border";
+    assertXPath(pStyles, sHdrBorder + "/x:bottom", "style", u"medium");
+    assertXPath(pStyles, sHdrBorder + "/x:left", 0);
+    assertXPath(pStyles, sHdrBorder + "/x:right", 0);
+    assertXPath(pStyles, sHdrBorder + "/x:top", 0);
 }
 
 CPPUNIT_TEST_FIXTURE(ScExportTest6, testTableStyleCustomRoundtripXLSX)

sc/source/filter/excel/xestyle.cxx

@@ -1869,12 +1869,16 @@ static const char* ToLineStyle( sal_uInt8 nLineStyle )
 
 namespace
 {
-void lcl_WriteBorder(XclExpXmlStream& rStrm, sal_Int32 nElement, sal_uInt8 nLineStyle, const Color& rColor, model::ComplexColor const& rComplexColor)
+void lcl_WriteBorder(XclExpXmlStream& rStrm, sal_Int32 nElement, sal_uInt8 nLineStyle, const Color& rColor, model::ComplexColor const& rComplexColor, bool bWriteEmpty = true)
 {
     sax_fastparser::FSHelperPtr& rStyleSheet = rStrm.GetCurrentStream();
     if( nLineStyle == EXC_LINE_NONE )
     {
-        rStyleSheet->singleElement(nElement);
+        // In a differential format (dxf) an empty side element (e.g. <left/>) means
+        // "no border" and overrides the underlying table style, so omit it there and
+        // let the side be inherited. The cell border list still writes it.
+        if (bWriteEmpty)
+            rStyleSheet->singleElement(nElement);
         return;
     }
     else if (rColor == Color(0, 0, 0) && !rComplexColor.isValidThemeType())
@@ -1889,7 +1893,7 @@ void lcl_WriteBorder(XclExpXmlStream& rStrm, sal_Int32 nElement, sal_uInt8 nLine
 }
 } // end anonymous namespace
 
-void XclExpCellBorder::SaveXml(XclExpXmlStream& rStream) const
+void XclExpCellBorder::SaveXml(XclExpXmlStream& rStream, bool bDxf) const
 {
     sax_fastparser::FSHelperPtr& rStyleSheet = rStream.GetCurrentStream();
 
@@ -1901,11 +1905,11 @@ void XclExpCellBorder::SaveXml(XclExpXmlStream& rStream) const
             // OOXTODO: XML_outline
     );
 
-    lcl_WriteBorder(rStream, XML_left, mnLeftLine, rPalette.GetColor(mnLeftColor), maComplexColorLeft);
-    lcl_WriteBorder(rStream, XML_right, mnRightLine, rPalette.GetColor(mnRightColor), maComplexColorRight);
-    lcl_WriteBorder(rStream, XML_top, mnTopLine, rPalette.GetColor(mnTopColor), maComplexColorTop);
-    lcl_WriteBorder(rStream, XML_bottom, mnBottomLine, rPalette.GetColor(mnBottomColor), maComplexColorBottom);
-    lcl_WriteBorder(rStream, XML_diagonal, mnDiagLine, rPalette.GetColor(mnDiagColor), maComplexColorDiagonal);
+    lcl_WriteBorder(rStream, XML_left, mnLeftLine, rPalette.GetColor(mnLeftColor), maComplexColorLeft, !bDxf);
+    lcl_WriteBorder(rStream, XML_right, mnRightLine, rPalette.GetColor(mnRightColor), maComplexColorRight, !bDxf);
+    lcl_WriteBorder(rStream, XML_top, mnTopLine, rPalette.GetColor(mnTopColor), maComplexColorTop, !bDxf);
+    lcl_WriteBorder(rStream, XML_bottom, mnBottomLine, rPalette.GetColor(mnBottomColor), maComplexColorBottom, !bDxf);
+    lcl_WriteBorder(rStream, XML_diagonal, mnDiagLine, rPalette.GetColor(mnDiagColor), maComplexColorDiagonal, !bDxf);
 
     // Inner borders (vertical/horizontal). Only emitted when actually set, so
     // ordinary cell borders keep their previous output.
@@ -3350,7 +3354,7 @@ void XclExpDxf::SaveXml( XclExpXmlStream& rStrm )
     if (mpAlign)
         mpAlign->SaveXml(rStrm);
     if (mpBorder)
-        mpBorder->SaveXml(rStrm);
+        mpBorder->SaveXml(rStrm, /*bDxf*/true);
     if (mpProt)
         mpProt->SaveXml(rStrm);
     if (mpCellArea)
@@ -3372,7 +3376,7 @@ void XclExpDxf::SaveXmlExt( XclExpXmlStream& rStrm )
     if (mpAlign)
         mpAlign->SaveXml(rStrm);
     if (mpBorder)
-        mpBorder->SaveXml(rStrm);
+        mpBorder->SaveXml(rStrm, /*bDxf*/true);
     if (mpProt)
         mpProt->SaveXml(rStrm);
     rStyleSheet->endElementNS( XML_x14, XML_dxf );

sc/source/filter/inc/xestyle.hxx

@@ -382,7 +382,8 @@ struct XclExpCellBorder : public XclCellBorder
     /** Fills the data to the passed fields of a BIFF8 CF (conditional format) record. */
     void                FillToCF8( sal_uInt16& rnLine, sal_uInt32& rnColor ) const;
 
-    void                SaveXml( XclExpXmlStream& rStrm ) const;
+    /// bDxf: omit unset border sides (dxf) instead of writing them as empty elements.
+    void                SaveXml( XclExpXmlStream& rStrm, bool bDxf = false ) const;
 };
 
 /** Extends the XclCellArea struct for export.