fix: wire up measure-numbering read/write in mx::api

src/private/mx/impl/MeasureReader.cpp

@@ -815,10 +815,13 @@ void MeasureReader::parsePrint(const core::Print &inMxPrint) const
     // Per-measure <print> layout is read at the score level, keyed by
     // measure index, in ScoreReader::scanForSystemInfo and
     // ScoreReader::scanForPageInfo (which capture new-system, new-page,
-    // page-number, system-layout, staff-layout, and page-layout). The
-    // per-measure music-data hook has no api home of its own, so nothing
-    // is captured here.
-    MX_UNUSED(inMxPrint);
+    // page-number, system-layout, staff-layout, and page-layout).
+    // measure-numbering is measure-scoped api state (MeasureData::measureNumbering,
+    // not carried forward like time/key), so it is captured directly here instead.
+    if (inMxPrint.measureNumbering().has_value())
+    {
+        myOutMeasureData.measureNumbering = myConverter.convertMeasureNumbering(inMxPrint.measureNumbering()->value());
+    }
 }
 
 void MeasureReader::parseSound(const core::Sound &inMxSound) const

src/private/mx/impl/MeasureWriter.cpp

@@ -15,6 +15,7 @@
 #include "mx/core/generated/LayoutGroup.h"
 #include "mx/core/generated/LeftRightMarginsGroup.h"
 #include "mx/core/generated/MarginType.h"
+#include "mx/core/generated/MeasureNumbering.h"
 #include "mx/core/generated/MusicDataChoice.h"
 #include "mx/core/generated/PageLayout.h"
 #include "mx/core/generated/PageLayoutGroup.h"
@@ -108,6 +109,11 @@ void MeasureWriter::writeMeasureGlobals()
         writePageInfo(*pageData);
     }
 
+    if (myMeasureData.measureNumbering != api::MeasureNumbering::unspecified)
+    {
+        writeMeasureNumbering();
+    }
+
     if (myHistory.getCursor().isFirstMeasureInPart)
     {
         myPropertiesWriter->writeDivisions(myHistory.getCursor().getGlobalTicksPerQuarter());
@@ -375,6 +381,51 @@ void MeasureWriter::writePageInfo(const api::PageData &inPageData)
     }
 }
 
+void MeasureWriter::writeMeasureNumbering()
+{
+    // Same find-or-create <print> merge pattern as writePageInfo(): measure-numbering shares
+    // the <print> element with any system/page layout already written for this measure.
+    const auto existingData = myOutMeasure.musicData();
+    int printIndex = -1;
+    int idx = 0;
+    for (const auto &mdc : existingData)
+    {
+        if (mdc.isPrint())
+        {
+            printIndex = idx;
+            break;
+        }
+        ++idx;
+    }
+
+    core::Print outPrint{};
+    if (printIndex >= 0)
+    {
+        outPrint = existingData[printIndex].asPrint();
+    }
+
+    core::MeasureNumbering outMeasureNumbering{};
+    outMeasureNumbering.setValue(myConverter.convertMeasureNumbering(myMeasureData.measureNumbering));
+    outPrint.setMeasureNumbering(std::move(outMeasureNumbering));
+
+    if (printIndex >= 0)
+    {
+        std::vector<core::MusicDataChoice> newData;
+        newData.reserve(existingData.size());
+        int i = 0;
+        for (const auto &mdc : existingData)
+        {
+            newData.push_back(i == printIndex ? core::MusicDataChoice::print(outPrint) : mdc);
+            ++i;
+        }
+        myOutMeasure.setMusicData(std::move(newData));
+    }
+    else
+    {
+        myOutMeasure.addMusicData(core::MusicDataChoice::print(outPrint));
+    }
+}
+
 void MeasureWriter::writeStaves()
 {
     myHistory.resetCursorFofStaffIterations();

src/private/mx/impl/MeasureWriter.h

@@ -207,6 +207,7 @@ class MeasureWriter
     void writeMeasureGlobals();
     void writeSystemInfo();
     void writePageInfo(const api::PageData &inNewPageData);
+    void writeMeasureNumbering();
     void writeStaves();
     void writeVoices(const api::StaffData &inStaff);
     void writeForwardOrBackupIfNeeded(const api::NoteData &currentNote);

src/private/mxtest/api/MeasureDataTest.cpp

@@ -262,4 +262,45 @@ TEST(staffLinesAndStaffSizeRoundTrip, MeasureData)
 
 T_END;
 
+TEST(measureNumberingRoundTrip, MeasureData)
+{
+    ScoreData score;
+    score.parts.emplace_back();
+    auto &part = score.parts.back();
+    part.measures.emplace_back();
+    auto &measure = part.measures.back();
+    measure.measureNumbering = MeasureNumbering::system;
+    measure.staves.emplace_back();
+    measure.staves.back().voices[0].notes.emplace_back();
+
+    const auto xml = mxtest::toXml(score);
+    CHECK(xml.find("<measure-numbering>system</measure-numbering>") != std::string::npos);
+
+    const auto outScore = mxtest::fromXml(xml);
+    CHECK_EQUAL(1, outScore.parts.size());
+    CHECK_EQUAL(1, outScore.parts.front().measures.size());
+    CHECK(MeasureNumbering::system == outScore.parts.front().measures.front().measureNumbering);
+}
+
+T_END;
+
+TEST(measureNumberingUnspecifiedOmitsElement, MeasureData)
+{
+    ScoreData score;
+    score.parts.emplace_back();
+    auto &part = score.parts.back();
+    part.measures.emplace_back();
+    auto &measure = part.measures.back();
+    measure.staves.emplace_back();
+    measure.staves.back().voices[0].notes.emplace_back();
+
+    const auto xml = mxtest::toXml(score);
+    CHECK(xml.find("<measure-numbering>") == std::string::npos);
+
+    const auto outScore = mxtest::fromXml(xml);
+    CHECK(MeasureNumbering::unspecified == outScore.parts.front().measures.front().measureNumbering);
+}
+
+T_END;
+
 #endif

src/private/mxtest/api/roundtrip-baseline.txt

@@ -293,3 +293,8 @@ lysuite/ly01a_Pitches_Pitches.xml
 lysuite/ly01e_Pitches_ParenthesizedAccidentals.xml
 lysuite/ly01f_Pitches_ParenthesizedMicrotoneAccidentals.xml
 musuite/testAccidentals2.xml
+
+# Unblocked by wiring MeasureData::measureNumbering through MeasureReader/
+# MeasureWriter: the field and its Converter existed but neither side ever
+# called it, so <measure-numbering> was silently dropped on round-trip.
+ksuite/k015a_System_Layout.xml