[ios] predicateWithMGLJSONObject can return Invalid filter value: filter property must be a string

[mfazekas]

Using predicateWithMGLJSONObject can return Invalid filter value: filter property must be a string for a valid expression because of NSPredicate conversion.

Steps to reproduce

        statesLayer.predicate = [NSPredicate predicateWithMGLJSONObject: @[
                                                                           @"all",
                                                                           @[@"==", @"$type", @"Point"],
                                                                           @[@"in", @"type", @"Blue Project", @"WFW Project"]
                                                                           ]
                                 ];

Expected behavior

Expected to work.

Actual behavior

Raises exception:

'NSInvalidArgumentException', reason: 'Invalid filter value: filter property must be a string'
*** First throw call stack:
(
	0   CoreFoundation                      0x0000000107d5d6fb __exceptionPreprocess + 331
	1   libobjc.A.dylib                     0x000000010884cac5 objc_exception_throw + 48
	2   CoreFoundation                      0x0000000107d5d555 +[NSException raise:format:] + 197
	3   Mapbox                              0x0000000103c808f3 -[NSPredicate(MGLPrivateAdditions) mgl_filter] + 387
	4   Mapbox                              0x0000000103c9ac70 -[MGLFillStyleLayer setPredicate:] + 928

Configuration

Mapbox SDK versions: 316584f - 5.1.0.alpha1
iOS/macOS versions: 12.2/10.14.4
Device/simulator models: iPhone X
Xcode version: 10.2.1

[mfazekas]

See https://github.com/react-native-mapbox-gl/maps/issues/70

The issue seems to be that the following JSON

[
    'all',
   ['==', '$type', 'Point'],
   ['in', 'type', 'Blue Project', 'WFW Project']
]

Becomes the following NSPredicate for NSPredicate predicateWithMGLJSONObject

"$type" == "Point" AND MGL_FUNCTION("in", "type", "Blue Project", "WFW Project") == 1

And for that predicate.mgl_jsonExpressionObject

[
     'all',
     ['==', '$type', 'Point'],
     ['==', ['in', 'type', 'Blue Project', 'WFW Project'], 1]
]

And it sounds like the first argument to == is expected to be a string not an array.

Seems to be coming from

mapbox-gl-native/src/mbgl/style/conversion/filter.cpp

Lines 132 to 146 in 3ceabcd

	ParseResult convertLegacyComparisonFilter(const Convertible& values, Error& error, optional<std::string> opOverride = {}) {
	optional<std::string> op = opOverride ? opOverride : toString(arrayMember(values, 0));
	optional<std::string> property = toString(arrayMember(values, 1));
	if (!property) {
	error.message = "filter property must be a string";
	return {};
	} else if (*property == "$type") {
	return createExpression("filter-type-" + *op, convertLiteralArray(values, error, 2), error);
	} else if (*property == "$id") {
	return createExpression("filter-id-" + *op, convertLiteralArray(values, error, 2), error);
	} else {
	return createExpression("filter-" + *op, convertLiteralArray(values, error, 1), error);
	}
	}

and

mapbox-gl-native/src/mbgl/style/conversion/filter.cpp

Lines 207 to 211 in 3ceabcd

	*op == "==" ||
	*op == "<" ||
	*op == ">" ||
	*op == "<=" ||
	*op == ">=" ? convertLegacyComparisonFilter(values, error) :

[julianrex]

Thanks for the detailed report @mfazekas!

[1ec5]

all and in are part of the filter syntax in the style specification. Filters are deprecated and are no longer supported in the native SDKs. You should use an expression instead.

[mfazekas]

@1ec5 I'm a bit confused. The expression docs you're referring to shows all as a valid expression.

[mfazekas]

@1ec5 nevermind if i convert "in" to expression from legacy filter as well it works fine:

@[
       @"all",
        @[@"==", @[@"geometry-type"], @"Point"],
        @[@"match",
                 @[@"get", @"type"],
                 @[@"Blue Project", @"WFW Project"], @YES,
                 @NO]
           ]