sw XHTML export: use CSS instead of <center> for tables

<center> is not valid XHTML, have to use CSS styling instead.

HTML export uses <center> by default around tables where the alignment
is center.

Fix the problem by avoiding <center> in the XHTML case and set the left
and right margin to auto, which means:

If the values of margin-left and margin-right are both auto, the
calculated space is evenly distributed.

according to
<https://developer.mozilla.org/en-US/docs/Web/CSS/margin-left>.

The import will be adjusted to recognize the new markup in a follow-up
change.

Change-Id: I51e3507e9cde713f961b783378d66db59194a6ca
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/145814
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

3 files changed, 53 insertions, 2 deletions

diff --git a/sw/qa/filter/html/html.cxx b/sw/qa/filter/html/html.cxx
index 537b437c4bdb..65f67b7378d1 100644
--- a/sw/qa/filter/html/html.cxx
+++ b/sw/qa/filter/html/html.cxx
@@ -196,6 +196,36 @@ CPPUNIT_TEST_FIXTURE(Test, testTableRowSpanInAllCells)
     assertXPathNoAttribute(pHtmlDoc, "//tr[1]/td[1]", "rowspan");
     assertXPath(pHtmlDoc, "//tr", 1);
 }
+
+CPPUNIT_TEST_FIXTURE(Test, testCenteredTableCSSExport)
+{
+    // Given a document with a centered table:
+    createSwDoc();
+    SwDoc* pDoc = getSwDoc();
+    SwWrtShell* pWrtShell = pDoc->GetDocShell()->GetWrtShell();
+    SwInsertTableOptions aTableOptions(SwInsertTableFlags::NONE, 0);
+    pWrtShell->InsertTable(aTableOptions, 1, 1);
+    pWrtShell->MoveTable(GotoPrevTable, fnTableStart);
+    SfxItemSetFixed<RES_FRMATR_BEGIN, RES_FRMATR_END - 1> aSet(pWrtShell->GetAttrPool());
+    SwFormatHoriOrient aHoriOrientItem(/*nX=*/0, text::HoriOrientation::CENTER);
+    aSet.Put(aHoriOrientItem);
+    pWrtShell->SetTableAttr(aSet);
+
+    // When exporting to XHTML:
+    setFilterOptions("xhtmlns=reqif-xhtml");
+    save("HTML (StarWriter)");
+
+    // Then make sure that CSS is used to horizontally position the table:
+    SvMemoryStream aStream;
+    WrapReqifFromTempFile(aStream);
+    xmlDocUniquePtr pXmlDoc = parseXmlStream(&aStream);
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 0
+    // - Actual  : 1
+    // i.e <center> was used to position the table, not CSS.
+    assertXPath(pXmlDoc, "//reqif-xhtml:center", 0);
+    assertXPath(pXmlDoc, "//reqif-xhtml:table", "style", "margin-left: auto; margin-right: auto");
+}
 }
 
 CPPUNIT_PLUGIN_IMPLEMENT();
diff --git a/sw/source/filter/html/css1atr.cxx b/sw/source/filter/html/css1atr.cxx
index 135494df00ca..28c5cc5dea8f 100644
--- a/sw/source/filter/html/css1atr.cxx
+++ b/sw/source/filter/html/css1atr.cxx
@@ -2064,6 +2064,17 @@ void SwHTMLWriter::OutCSS1_TableFrameFormatOptions( const SwFrameFormat& rFrameF
     if( SfxItemState::SET==rItemSet.GetItemState( RES_LAYOUT_SPLIT, false, &pItem ) )
         OutCSS1_SwFormatLayoutSplit( *this, *pItem );
 
+    if (mbXHTML)
+    {
+        sal_Int16 eTabHoriOri = rFrameFormat.GetHoriOrient().GetHoriOrient();
+        if (eTabHoriOri == text::HoriOrientation::CENTER)
+        {
+            // Emit XHTML's center using inline CSS.
+            OutCSS1_Property(sCSS1_P_margin_left, "auto", nullptr, sw::Css1Background::Table);
+            OutCSS1_Property(sCSS1_P_margin_right, "auto", nullptr, sw::Css1Background::Table);
+        }
+    }
+
     if( !m_bFirstCSS1Property )
         Strm().WriteChar( '\"' );
 }
diff --git a/sw/source/filter/html/htmltabw.cxx b/sw/source/filter/html/htmltabw.cxx
index ddb8c8eb5f10..a1dee0f75333 100644
--- a/sw/source/filter/html/htmltabw.cxx
+++ b/sw/source/filter/html/htmltabw.cxx
@@ -1113,7 +1113,13 @@ Writer& OutHTML_SwTableNode( Writer& rWrt, SwTableNode & rNode,
         if( rHTMLWrt.m_bLFPossible )
             rHTMLWrt.OutNewLine();  // <CENTER> in new line
         if( text::HoriOrientation::CENTER==eDivHoriOri )
-            HTMLOutFuncs::Out_AsciiTag( rWrt.Strm(), Concat2View(rHTMLWrt.GetNamespace() + OOO_STRING_SVTOOLS_HTML_center) );
+        {
+            if (!rHTMLWrt.mbXHTML)
+            {
+                // Not XHTML's css center: start <center>.
+                HTMLOutFuncs::Out_AsciiTag( rWrt.Strm(), Concat2View(rHTMLWrt.GetNamespace() + OOO_STRING_SVTOOLS_HTML_center) );
+            }
+        }
         else
         {
             OStringLiteral sOut = OOO_STRING_SVTOOLS_HTML_division
@@ -1166,7 +1172,11 @@ Writer& OutHTML_SwTableNode( Writer& rWrt, SwTableNode & rNode,
         OString aTag = text::HoriOrientation::CENTER == eDivHoriOri
                            ? OOO_STRING_SVTOOLS_HTML_center
                            : OOO_STRING_SVTOOLS_HTML_division;
-        HTMLOutFuncs::Out_AsciiTag(rWrt.Strm(), Concat2View(rHTMLWrt.GetNamespace() + aTag), false);
+        if (!rHTMLWrt.mbXHTML || eDivHoriOri != text::HoriOrientation::CENTER)
+        {
+            // Not XHTML's css center: end <center>.
+            HTMLOutFuncs::Out_AsciiTag(rWrt.Strm(), Concat2View(rHTMLWrt.GetNamespace() + aTag), false);
+        }
         rHTMLWrt.m_bLFPossible = true;
     }