GDALWarp: Allow INIT_DEST=NO_DATA without NoData, for now

See OSGeo#12189

Author: dbaston

alg/gdalwarpoperation.cpp

@@ -801,7 +801,9 @@ CPLErr GDALWarpOperation::InitializeDestinationBuffer(void *pDstBuffer,
         {
             if (psOptions->padfDstNoDataReal == nullptr)
             {
-                CPLError(CE_Failure, CPLE_AppDefined,
+                // TODO: Change to CE_Failure for GDAL 3.12
+                // See https://github.com/OSGeo/gdal/pull/12189
+                CPLError(CE_Warning, CPLE_AppDefined,
                          "INIT_DEST was set to NO_DATA, but a NoData value was "
                          "not defined.");
                 return CE_Failure;

autotest/utilities/test_gdalwarp_lib.py

@@ -4391,7 +4391,9 @@ def test_gdalwarp_lib_init_dest_invalid(tmp_vsimem, init_dest):
 
 def test_gdalwarp_lib_init_dest_nodata_invalid(tmp_vsimem):
 
-    with pytest.raises(Exception, match="NoData value was not defined"):
+    # TODO: switch from warning to failure in GDAL 3.12
+    # with pytest.raises(Exception, match="NoData value was not defined"):
+    with gdaltest.error_raised(gdal.CE_Warning, "NoData value was not defined"):
         gdal.Warp(
             tmp_vsimem / "out.tif",
             "../gcore/data/byte.tif",