Remove “in” expression workaround

[1ec5]

Removed the match-based workaround for in expressions in favor of real support for an in expression operator, including support for testing whether a string is a substring of another string.

• Replace match-based workaround with in operator mappings
• Test substring matching
• Implement ANY/SOME and NONE with = and ALL with !=
• Document in expressions in “Information for Style Authors” guide
• Document comparison modifiers in “Predicates and Expressions” guide

Fixes #168. Depends on #181. Retarget and rebase this PR onto master before merging.

/cc @mapbox/maps-ios

[1ec5]

I threw in some additional support for NSExpression syntactic sugar so developers don’t feel like they have to match our examples exactly:

• ANY x = y is logically equivalent to x CONTAINS y and y IN x. All three forms evaluate to an in expression.
• ALL x != y is logically equivalent to NOT x CONTAINS y and NOT y IN x. All three forms evaluate to an in expression inside a ! expression.

[jmkiley]

I tested this PR out with point features with a title attribute. title had a string containing feature for all three, but I wasn't able to get any features with [NSPredicate predicateWithFormat:@"title CONTAINS 'feature'"]; Also tested with IN and didn't have any luck.

Sample code

MGLPointFeature *pointfeature1 = [[MGLPointFeature alloc] init];
pointfeature1.coordinate = CLLocationCoordinate2DMake(0, 33);
[pointfeature1 setAttributes:@{@"title": [NSString stringWithFormat:@"feature-%f", pointfeature1.coordinate.longitude]}];

MGLPointFeature *pointfeature2 = [[MGLPointFeature alloc] init];
pointfeature2.coordinate = CLLocationCoordinate2DMake(0, 66);
[pointfeature2 setAttributes:@{@"title": [NSString stringWithFormat:@"feature"]}];

MGLPointFeature *pointfeature3 = [[MGLPointFeature alloc] init];
pointfeature3.coordinate = CLLocationCoordinate2DMake(0, 99);
[pointfeature3 setAttributes:@{@"title": [NSString stringWithFormat:@"feature"]}];
                                           
NSArray *points = @[pointfeature1, pointfeature2, pointfeature3];
MGLShapeSource *source = [[MGLShapeSource alloc] initWithIdentifier:@"source" features:points options:nil];

[style addSource:source];

MGLCircleStyleLayer *layer = [[MGLCircleStyleLayer alloc] initWithIdentifier:@"layer" source:source];
layer.predicate = [NSPredicate predicateWithFormat:@"title CONTAINS 'feature'"];
layer.circleRadius = [NSExpression expressionForConstantValue:@40];
[style addLayer:layer];

[jmkiley]

Noting that CONTAINS seems to work in combination with the NOT operator. Two circles displayed with [NSPredicate predicateWithFormat:@"NOT title CONTAINS '33'"];.

Also, using CONTAINS with an NSExpression works. For example, I saw one circle with layer.circleOpacity = [NSExpression expressionWithFormat:@"TERNARY(title CONTAINS '33', 1, 0)"];.

[1ec5]

I tested this PR out with point features with a title attribute. title had a string containing feature for all three, but I wasn't able to get any features with [NSPredicate predicateWithFormat:@"title CONTAINS 'feature'"];

Thanks for noticing that: mapbox/mapbox-gl-native#16262.

[fabian-guerra]

Thank you! Using match for in expressions what kind of problematic. With this change it became simpler.

[fabian-guerra]

👏🏼 this is simple

[1ec5]

I tested this PR out with point features with a title attribute. title had a string containing feature for all three, but I wasn't able to get any features with [NSPredicate predicateWithFormat:@"title CONTAINS 'feature'"];

Thanks for noticing that: mapbox/mapbox-gl-native#16262.

in filters have been fixed in mbgl, and #210 will pull in that fix. No additional changes will be needed at the SDK level to support IN in predicates, but I’d like to add unit tests that round-trip between NSPredicate and mbgl filters, which will depend on #210.