Qgz files created with this plugin do not contain a `mapcanvas` element

[spwoodcock]

Observation

• I'm no expert in QGIS file formats / XML, so correct me if I'm wrong here.
• I swapped over from the XLSFormConverter plugin to using this, for generating projects to upload to QFieldCloud.
• The resulting projects load fine in QGIS and QField, but in the app.qfield.cloud UI I get an error:

• The resulting project is shown with a red dot, and cannot be viewed in QField when logged into the relevant account.

Analysis

• Digging into the generated .qgs XML, I can see the mapcanvas element doesn't exist.
• QFieldCloud's process_projectfile worker searches for this element by name to to extract the project extent and background colour.
• Projects generated with this plugin omit referencing the mapcanvas, as it doesn't involve a GUI (while the XLSFormConverter plugin did have an attached GUI context).

So either:

1. This plugin should add a mapcontext element.
2. QFieldCloud qgz processing should fail gracefully if no project extent or background colour is found.

---

I used Opus 4.6 to create a function that injects the mapcanvas element. The tool I am working on uses this & the projects are now green in QFC:

def _inject_map_canvas(
    qgs_data: bytes, extent_bbox: list, log: logging.Logger
) -> tuple[bytes, bool]:
    """Inject <mapcanvas name="theMapCanvas"> if absent.

    QFieldCloud's process_projectfile worker searches for this element by name
    to extract the project extent and background colour.  Projects generated by
    xlsform2qgis omit it because QGIS only writes it when a QgsMapCanvas
    object is attached (GUI context only).
    """
    if b'name="theMapCanvas"' in qgs_data:
        return qgs_data, False

    # Grab the <spatialrefsys> block from <projectCrs> to reuse as <destinationsrs>
    crs_m = re.search(
        rb"<projectCrs>\s*(<spatialrefsys\b.*?</spatialrefsys>)\s*</projectCrs>",
        qgs_data,
        re.DOTALL,
    )
    if not crs_m:
        log.warning(
            "Cannot inject theMapCanvas: no <projectCrs> found in project XML"
        )
        return qgs_data, False

    srs_block = crs_m.group(1)

    # Derive map units from the CRS projection acronym
    acronym_m = re.search(rb"<projectionacronym>(.*?)</projectionacronym>", srs_block)
    acronym = acronym_m.group(1).decode() if acronym_m else ""
    units = "degrees" if acronym == "longlat" else "meters"

    xmin, ymin, xmax, ymax = extent_bbox
    canvas_xml = (
        f'\n  <mapcanvas name="theMapCanvas" annotationsVisible="1">\n'
        f"    <units>{units}</units>\n"
        f"    <extent>\n"
        f"      <xmin>{xmin}</xmin>\n"
        f"      <ymin>{ymin}</ymin>\n"
        f"      <xmax>{xmax}</xmax>\n"
        f"      <ymax>{ymax}</ymax>\n"
        f"    </extent>\n"
        f"    <rotation>0</rotation>\n"
        f"    <destinationsrs>\n"
        f"      {srs_block.decode()}\n"
        f"    </destinationsrs>\n"
        f"    <rendermaptile>0</rendermaptile>\n"
        f"  </mapcanvas>"
    ).encode()

    # Insert right after </verticalCrs> (preferred) or </projectCrs> (fallback)
    for anchor in (b"</verticalCrs>", b"</projectCrs>"):
        if anchor in qgs_data:
            updated = qgs_data.replace(anchor, anchor + canvas_xml, 1)
            log.info("Injected <mapcanvas name=\"theMapCanvas\"> into project XML")
            return updated, True

    log.warning("Could not find insertion point for theMapCanvas in project XML")
    return qgs_data, False

[spwoodcock]

I searched the repo for mapcanvas and the weird thing is it seems the logic to add it in is there (from 4 months ago): https://github.com/opengisch/xlsform2qgis/blame/596fa30521ce2a2ca39185eca721e8af5a94cefe/src/xlsform2qgis/converter.py#L1033

I'm testing with the most up to date main branch though:

pip install --no-warn-script-location --break-system-packages \
      --no-cache-dir \
      git+https://github.com/opengisch/xlsform2qgis.git

and using it like so:

    from xlsform2qgis.converter import XLSFormConverter
    converter = XLSFormConverter(str(xlsform_path))

    if not converter.is_valid():
        raise RuntimeError("The provided XLSForm is invalid, aborting.")
    converter.info.connect(lambda message: log.info(message))
    converter.warning.connect(lambda message: log.warning(message))
    converter.error.connect(lambda message: log.error(message))

    converter.set_custom_title(title)
    converter.set_preferred_language(language)
    converter.set_basemap("OpenStreetMap")
    converter.set_groups_as_tabs(True)
    converter.set_crs(crs)
    converter.set_extent(extent_rect)
    _configure_converter_edit_mode(converter, open_in_edit_mode, log)

    if features_gpkg_path:
        features_layer = QgsVectorLayer(features_gpkg_path, "features_valid", "ogr")
        if features_layer.isValid():
            converter.set_geometries(features_layer)
        else:
            log.warning(
                "Could not load features layer from %s, "
                "proceeding without features",
                features_gpkg_path,
            )

    return converter.convert(str(final_output_dir))

Interested to see if anyone else has the same problem in QFC, or it's just user error on my behalf! (in which case we can close this issue 🙌)