tdf#164095 sw: fix missing top margin on paragraph after changing page style

Open the bugdoc, go to the page after the section break, there is a top
margin for the first paragraph there in Word, but not in Writer.

This went wrong in commit abd90828cf
(tdf#160952 sw: ignore top margin of para on non-first pages with newer
DOCX, 2024-05-14), where it seemed that all implicit and explicit page
breaks want to ignore that top margin for the first paragraph.

Turns out this is more complex: implicit breaks and page breaks should
be followed by an ignore, but not paragraphs after "section break (next
page)". So restore the margins for the RES_PAGEDESC, but continue to
have them for RES_BREAK & implicit breaks.

Change-Id: If1fcf3077b81a705d3587bdae422dcfa16f1c17c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177973
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

sw/qa/core/layout/calcmove.cxx

@@ -84,6 +84,24 @@ CPPUNIT_TEST_FIXTURE(Test, testIgnoreTopMarginFly)
     CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(4000), nParaTopMargin);
 }
 
+CPPUNIT_TEST_FIXTURE(Test, testIgnoreTopMarginPageStyleChange)
+{
+    // Given a DOCX (>= Word 2013), section break (next page) between pages 2 and 3:
+    createSwDoc("ignore-top-margin-page-style-change.docx");
+
+    // When laying out that document:
+    xmlDocUniquePtr pXmlDoc = parseLayoutDump();
+
+    // Then make sure that the top margin is not ignored on page 3:
+    sal_Int32 nParaTopMargin
+        = getXPath(pXmlDoc, "/root/page[3]/body/txt/infos/prtBounds", "top").toInt32();
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 2000
+    // - Actual  : 0
+    // i.e. the top margin was ignored, which is incorrect.
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(2000), nParaTopMargin);
+}
+
 CPPUNIT_TEST_FIXTURE(Test, testHideWhitespaceGrowingLastPage)
 {
     // Given a document with a full first page, then hiding whitespace:

sw/source/core/layout/calcmove.cxx

@@ -1131,6 +1131,16 @@ bool SwFrame::IsCollapseUpper() const
         return false;
     }
 
+    // Avoid the ignore after applying a new page style (but do it after page breaks).
+    const SwTextNode* pTextNode = pTextFrame->GetTextNodeForParaProps();
+    if (pTextNode)
+    {
+        if (pTextNode->HasSwAttrSet() && pTextNode->GetSwAttrSet().HasItem(RES_PAGEDESC))
+        {
+            return false;
+        }
+    }
+
     return true;
 }