MapServer generates empty error messages: point vs. annotation layers

[jdoyon@…]

This is kind of hard to nail down, but in my upgrades from 3.6.6 to 4.6.1, I
discovered that MapServer got much pickyer about whether to use point vs.
annotation TYPE.

Under certain circumstances, MapServer will generate an error, but with no
message, which is hard to track down :)

The latest example of this for me was:

  LAYER
    NAME featureannotate
    TYPE annotation
    STATUS off
    DATA geo_np
    METADATA
      LEGEND_GROUP "theme"
      GROUP_CONTROLLER "0"
      LAY_TITLE "Annotation layer for feature"
      CHECKABLE "0"
      LEGEND_ORDER "-1"
    END
    LABELITEM "FEATURE_NA"
    CLASSITEM "UNIQUE_KEY"
    CLASS
      EXPRESSION "w8g9q7regc87ctr8743tbca084ytc"
      SIZE 30
      COLOR 0 0 0
      LABEL
        TYPE TRUETYPE
        FONT "arial"
        SIZE 14
        COLOR 0 0 0
        OUTLINECOLOR 226 226 226
        POSITION ur
        FORCE TRUE
      END
    END
    PROJECTION
      "proj=latlong"
    END
  END

This works ok.

In 3.6.6, I had a "SYMBOL -1" for whatever reason.  If you add that in, you'll
get the mysterious "empty error".  I do sometimes set a symbol via CGI
parameters (map_layer_class_symbol) and that works fine.

When I migrated 100's of mapfiles, I ran into this quite a bit, having to
convert layers from "point" to "annotation"!

I suppose an actual error message would be nice, as well as better documentation
as to what can be point vs. what can be annotation?

Sorry for the fuzzy explanation!

J.F.

[jdoyon@…]

Ran into this again on some WMS mapfiles.

If this occurs over WMS and the error return is done "in image", then you'll see
a single ":" in the top left corner of the returned map image.  Which makes
enough sense once you think about it, but went hunting for this for a while,
since the error message wasn't obvious, it just looked like there were layers
that would mysteriously not show up on the map.