[core] Support two-argument shorthand for "match" expression

[jfirebaugh]

Companion to mapbox/mapbox-gl-js#6964.

Dependent on getting some ignores or fixes for some new render tests (cc @ChrisLoer):

• Fix in Use correct labelLength scale for text-max-angle/line-center mapbox-gl-js#6945
• Port symbol-placement: line-center to native #12337

@1ec5 Does this require any NSExpression-related work?

It looks like it should fit into this Android API naturally. I think it should have had a @Size(min = 4) annotation, but after this change @Size(min = 2) is correct. cc @tobrun

[1ec5]

Does this require any NSExpression-related work?

If a property getter in mbgl can return a match expression that uses the shorthand, then +[NSExpression expressionWithMGLJSONObject:] should detect that there’s only one argument and synthesize TRUE and FALSE output values.

mapbox-gl-native/platform/darwin/src/NSExpression+MGLAdditions.mm

Lines 949 to 962 in 192c611

	} else if ([op isEqualToString:@"match"]) {
	NSMutableArray *optionsArray = [NSMutableArray array];
	for (NSUInteger index = 0; index < argumentObjects.count; index++) {
	NSExpression *option = [NSExpression expressionWithMGLJSONObject:argumentObjects[index]];
	// match operators with arrays as matching values should not parse arrays as generic functions.
	if (index > 0 && index < argumentObjects.count - 1 && !(index % 2 == 0) && [argumentObjects[index] isKindOfClass:[NSArray class]]) {
	option = [NSExpression expressionForAggregate:MGLSubexpressionsWithJSONObjects(argumentObjects[index])];
	}
	[optionsArray addObject:option];
	}
	return [NSExpression expressionForFunction:@"MGL_MATCH"
	arguments:optionsArray];

The usual case for this shorthand would be as part of a predicate rather than an expression set on a property. That’ll already work OK, thanks to this fallback that stuffs the expression in an == TRUE expression:

mapbox-gl-native/platform/darwin/src/NSPredicate+MGLAdditions.mm

Lines 157 to 162 in 192c611

	NSExpression *expression = [NSExpression expressionWithMGLJSONObject:object];
	return [NSComparisonPredicate predicateWithLeftExpression:expression
	rightExpression:[NSExpression expressionForConstantValue:@YES]
	modifier:NSDirectPredicateModifier
	type:NSEqualToPredicateOperatorType
	options:0];

It would be nice for ["match", ["get", "type"], ["a", "b", "c"]] to translate to type IN {'a', 'b', 'c'} rather than MGL_MATCH(type, {'a', 'b', 'c'}, TRUE, FALSE) == TRUE, but that can be tail work if necessary.

Conversely, the latter two arguments to this match expression can be omitted, though there shouldn’t be any functional difference:

mapbox-gl-native/platform/darwin/src/NSComparisonPredicate+MGLAdditions.mm

Lines 119 to 123 in 192c611

	NSExpression *matchExpression = [NSExpression expressionForFunction:@"MGL_MATCH"
	arguments:@[self.leftExpression,
	self.rightExpression,
	[NSExpression expressionForConstantValue:@YES],
	[NSExpression expressionForConstantValue:@NO]]];

/cc @fabian-guerra

[jfirebaugh]

If a property getter in mbgl can return a match expression that uses the shorthand, then +[NSExpression expressionWithMGLJSONObject:] should detect that there’s only one argument and synthesize TRUE and FALSE output values.

The shorthand is converted to longhand at parse time, so property getters will return the longhand form.

[stale]

This pull request has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.

[tobrun]

Closing since no one seems to be a strong yes on this feature

From mapbox/mapbox-gl-js#6964 (comment)