fix: Avoid casting to table type when select= and media type handler are used

Previously using a generic mimetype handler failed when any kind of select= was given, because
we tried to cast the select-result to the original table type. With this change, this cast is
only applied when select=* is given implicitly or explicitly. This is the only case where this
makes sense, because this guarantees that correct columns are selected in the correct order for
this cast to succeed.

Resolves #3160

src/PostgREST/Query/SqlFragment.hs

@@ -85,7 +85,8 @@ import PostgREST.Plan.Types              (CoercibleField (..),
 import PostgREST.RangeQuery              (NonnegRange, allRange,
                                           rangeLimit, rangeOffset)
 import PostgREST.SchemaCache.Identifiers (FieldName,
-                                          QualifiedIdentifier (..))
+                                          QualifiedIdentifier (..),
+                                          RelIdentifier (..))
 import PostgREST.SchemaCache.Routine     (MediaHandler (..),
                                           Routine (..),
                                           funcReturnsScalar,
@@ -221,10 +222,11 @@ asJsonF rout strip
 asGeoJsonF ::  SQL.Snippet
 asGeoJsonF = "json_build_object('type', 'FeatureCollection', 'features', coalesce(json_agg(ST_AsGeoJSON(_postgrest_t)::json), '[]'))"
 
-customFuncF :: Maybe Routine -> QualifiedIdentifier -> QualifiedIdentifier -> SQL.Snippet
-customFuncF rout funcQi target
+customFuncF :: Maybe Routine -> QualifiedIdentifier -> RelIdentifier -> SQL.Snippet
+customFuncF rout funcQi _
   | (funcReturnsScalar <$> rout) == Just True = fromQi funcQi <> "(_postgrest_t.pgrst_scalar)"
-  | otherwise                                 = fromQi funcQi <> "(_postgrest_t::" <> fromQi target <> ")"
+customFuncF _ funcQi RelAnyElement            = fromQi funcQi <> "(_postgrest_t)"
+customFuncF _ funcQi (RelId target)           = fromQi funcQi <> "(_postgrest_t::" <> fromQi target <> ")"
 
 locationF :: [Text] -> SQL.Snippet
 locationF pKeys = [qc|(
@@ -559,12 +561,12 @@ setConfigWithConstantNameJSON prefix keyVals = [setConfigWithConstantName (prefi
     arrayByteStringToText :: [(ByteString, ByteString)] -> [(Text,Text)]
     arrayByteStringToText keyVal = (T.decodeUtf8 *** T.decodeUtf8) <$> keyVal
 
-handlerF :: Maybe Routine -> QualifiedIdentifier -> MediaHandler -> SQL.Snippet
-handlerF rout target = \case
+handlerF :: Maybe Routine -> MediaHandler -> SQL.Snippet
+handlerF rout = \case
   BuiltinAggArrayJsonStrip   -> asJsonF rout True
   BuiltinAggSingleJson strip -> asJsonSingleF rout strip
   BuiltinOvAggJson           -> asJsonF rout False
   BuiltinOvAggGeoJson        -> asGeoJsonF
   BuiltinOvAggCsv            -> asCsvF
-  CustomFunc funcQi          -> customFuncF rout funcQi target
+  CustomFunc funcQi target   -> customFuncF rout funcQi target
   NoAgg                      -> "''::text"