[ios, macos] Add to-rgba expression operator. (#11725)

* [ios, macos] Add expression support to to-rgba operator.

* [ios, macos] Update style docs.

* [ios, macos] Refactored to-rgba to to-color.

* [ios, macos] Add support for to-rgba expression operator.

* [ios, macos] Add multiple parameters support to to-color operand.

* [ios, macos] Enable to-rgba operator for MGLColor or key path expressions.

* [ios, macos] Update predicates and expressions guide to reflect cast changes.

* [ios, macos] Update changelogs.

* [ios, macos] Clarify color casting usage.

10 files changed, 87 insertions, 9 deletions

diff --git a/platform/darwin/docs/guides/For Style Authors.md.ejs b/platform/darwin/docs/guides/For Style Authors.md.ejs
index b0ded7bc03..60177e57c2 100644
--- a/platform/darwin/docs/guides/For Style Authors.md.ejs
+++ b/platform/darwin/docs/guides/For Style Authors.md.ejs
@@ -335,7 +335,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `number`               | |
 `string`               | |
 `to-boolean`           | `boolValue` |
-`to-color`             | |
+`to-color`             | | `CAST(var, '<%- cocoaPrefix %>Color')`
 `to-number`            | `mgl_numberWithFallbackValues:` | `CAST(zipCode, 'NSNumber')`
 `to-string`            | `stringValue` | `CAST(ele, 'NSString')`
 `typeof`               | |
@@ -372,7 +372,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `rgb`                  | `+[UIColor colorWithRed:green:blue:alpha:]` |
 `rgba`                 | `+[UIColor colorWithRed:green:blue:alpha:]` |
 <% } -%>
-`to-rgba`              | |
+`to-rgba`              | | `CAST(noindex(var), 'NSArray')`
 `-`                    | `from:subtract:` | `2 - 1`
 `*`                    | `multiply:by:` | `1 * 2`
 `/`                    | `divide:by:` | `1 / 2`
diff --git a/platform/darwin/docs/guides/Predicates and Expressions.md b/platform/darwin/docs/guides/Predicates and Expressions.md
index c3b3d39a52..18eccda569 100644
--- a/platform/darwin/docs/guides/Predicates and Expressions.md
+++ b/platform/darwin/docs/guides/Predicates and Expressions.md
@@ -70,6 +70,8 @@ path or variable into a matching type:
 
 * To cast a value to a number, use `CAST(key, 'NSNumber')`.
 * To cast a value to a string, use `CAST(key, 'NSString')`.
+* To cast a value to a color, use `CAST(key, 'UIColor')` on iOS and `CAST(key, 'NSColor')` on macOS.
+* To cast an `NSColor` or `UIColor` object to an array, use `CAST(noindex(color), 'NSArray')`.
 
 For details about the predicate format string syntax, consult the “Predicate
 Format String Syntax” chapter of the
diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index b2bcf72caf..6dde705d3c 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -802,6 +802,22 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
         } else if ([op isEqualToString:@"to-string"] || [op isEqualToString:@"string"]) {
             NSExpression *operand = [NSExpression expressionWithMGLJSONObject:argumentObjects.firstObject];
             return [NSExpression expressionWithFormat:@"CAST(%@, 'NSString')", operand];
+        } else if ([op isEqualToString:@"to-color"]) {
+            NSExpression *operand = [NSExpression expressionWithMGLJSONObject:argumentObjects.firstObject];
+            
+            if (argumentObjects.count == 1) {
+#if TARGET_OS_IPHONE
+                return [NSExpression expressionWithFormat:@"CAST(%@, 'UIColor')", operand];
+#else
+                return [NSExpression expressionWithFormat:@"CAST(%@, 'NSColor')", operand];
+#endif
+            }
+            NSArray *subexpressions = MGLSubexpressionsWithJSONObjects(array);
+            return [NSExpression expressionForFunction:@"MGL_FUNCTION" arguments:subexpressions];
+            
+        } else if ([op isEqualToString:@"to-rgba"]) {
+            NSExpression *operand = [NSExpression expressionWithMGLJSONObject:argumentObjects.firstObject];
+            return [NSExpression expressionWithFormat:@"CAST(noindex(%@), 'NSArray')", operand];
         } else if ([op isEqualToString:@"get"]) {
             if (argumentObjects.count == 2) {
                 NSExpression *operand = [NSExpression expressionWithMGLJSONObject:argumentObjects.lastObject];
@@ -1165,6 +1181,26 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
                 } else if ([type isEqualToString:@"NSNumber"]) {
                     return @[@"to-number", object];
                 }
+#if TARGET_OS_IPHONE
+                else if ([type isEqualToString:@"UIColor"] || [type isEqualToString:@"MGLColor"]) {
+                    return @[@"to-color", object];
+                }
+#else
+                else if ([type isEqualToString:@"NSColor"] || [type isEqualToString:@"MGLColor"]) {
+                    return @[@"to-color", object];
+                }
+#endif
+                else if ([type isEqualToString:@"NSArray"]) {
+                    NSExpression *operand = self.arguments.firstObject;
+                    if ([operand expressionType] == NSFunctionExpressionType ) {
+                        operand = self.arguments.firstObject.arguments.firstObject;
+                    }
+                    if (([operand expressionType] != NSConstantValueExpressionType) ||
+                        ([operand expressionType] == NSConstantValueExpressionType &&
+                         [[operand constantValue] isKindOfClass:[MGLColor class]])) {
+                        return @[@"to-rgba", object];
+                    }
+                }
                 [NSException raise:NSInvalidArgumentException
                             format:@"Casting expression to %@ not yet implemented.", type];
             } else if ([function isEqualToString:@"MGL_FUNCTION"]) {
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 186cae609d..4ed1f61eb1 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -668,6 +668,38 @@ using namespace std::string_literals;
         XCTAssertEqualObjects([compatibilityExpression expressionValueWithObject:@{@"number": @1.5} context:nil], @"1.5");
         XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
     }
+    {
+#if TARGET_OS_IPHONE
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(x, 'UIColor')"];
+#else
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(x, 'NSColor')"];
+#endif
+        
+        NSArray *jsonExpression = @[@"to-color", @[@"get", @"x"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"MGL_FUNCTION('to-color', x, y, z)"];
+        NSArray *jsonExpression = @[@"to-color", @[@"get", @"x"], @[@"get", @"y"], @[@"get", @"z"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(noindex(x), 'NSArray')"];
+        NSArray *jsonExpression = @[@"to-rgba", @[@"get", @"x"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(noindex(%@), 'NSArray')", MGLConstantExpression(MGLColor.blueColor)];
+        NSArray *jsonExpression = @[@"to-rgba", @[@"rgb", @0, @0, @255]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(noindex('x'), 'NSArray')"];
+        XCTAssertThrowsSpecificNamed(expression.mgl_jsonExpressionObject, NSException, NSInvalidArgumentException);
+    }
 }
 
 - (void)testInterpolationExpressionObject {
diff --git a/platform/ios/CHANGELOG.md b/platform/ios/CHANGELOG.md
index d979021760..057149190c 100644
--- a/platform/ios/CHANGELOG.md
+++ b/platform/ios/CHANGELOG.md
@@ -22,6 +22,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Reduce per-frame render CPU time ([#11811](https://github.com/mapbox/mapbox-gl-native/issues/11811))
 * Fixed a crash when removing an `MGLOfflinePack`. ([#6092](https://github.com/mapbox/mapbox-gl-native/issues/6092))
 * Fixed an issue where an `MGLOverlay` object straddling the antimeridian had an empty `MGLOverlay.overlayBounds` value. ([#11783](https://github.com/mapbox/mapbox-gl-native/pull/11783))
+* Fixed an issue where certain colors were being misrepresented in `NSExpression` obtained from `MGLStyleLayer` getters. ([#11725](https://github.com/mapbox/mapbox-gl-native/pull/11725))
 
 ## 4.0.0 - April 19, 2018
 
diff --git a/platform/ios/docs/guides/For Style Authors.md b/platform/ios/docs/guides/For Style Authors.md
index 9a6e4428eb..d4fb17eb6a 100644
--- a/platform/ios/docs/guides/For Style Authors.md
+++ b/platform/ios/docs/guides/For Style Authors.md
@@ -325,7 +325,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `number`               | |
 `string`               | |
 `to-boolean`           | `boolValue` |
-`to-color`             | |
+`to-color`             | | `CAST(var, 'UIColor')`
 `to-number`            | `mgl_numberWithFallbackValues:` | `CAST(zipCode, 'NSNumber')`
 `to-string`            | `stringValue` | `CAST(ele, 'NSString')`
 `typeof`               | |
@@ -357,7 +357,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `upcase`               | `uppercase:` | `uppercase('Elysian Fields')`
 `rgb`                  | `+[UIColor colorWithRed:green:blue:alpha:]` |
 `rgba`                 | `+[UIColor colorWithRed:green:blue:alpha:]` |
-`to-rgba`              | |
+`to-rgba`              | | `CAST(noindex(var), 'NSArray')`
 `-`                    | `from:subtract:` | `2 - 1`
 `*`                    | `multiply:by:` | `1 * 2`
 `/`                    | `divide:by:` | `1 / 2`
diff --git a/platform/ios/src/UIColor+MGLAdditions.mm b/platform/ios/src/UIColor+MGLAdditions.mm
index 9ca39acda4..7c1fbddc20 100644
--- a/platform/ios/src/UIColor+MGLAdditions.mm
+++ b/platform/ios/src/UIColor+MGLAdditions.mm
@@ -66,7 +66,7 @@
     return [UIColor colorWithRed:[components[0].constantValue doubleValue] / 255.0
                            green:[components[1].constantValue doubleValue] / 255.0
                             blue:[components[2].constantValue doubleValue] / 255.0
-                           alpha:components.count == 3 ? [components[3].constantValue doubleValue] : 1.0];
+                           alpha:components.count == 3 ? 1.0 : [components[3].constantValue doubleValue]];
 }
 
 @end
diff --git a/platform/macos/CHANGELOG.md b/platform/macos/CHANGELOG.md
index d62ba2ea87..1ae0212b97 100644
--- a/platform/macos/CHANGELOG.md
+++ b/platform/macos/CHANGELOG.md
@@ -13,6 +13,7 @@
 * Fixed an issue where selecting an onscreen annotation could move the map unintentionally. ([#11731](https://github.com/mapbox/mapbox-gl-native/pull/11731))
 * Fixed a crash when removing an `MGLOfflinePack`. ([#6092](https://github.com/mapbox/mapbox-gl-native/issues/6092))
 * Fixed an issue where an `MGLOverlay` object straddling the antimeridian had an empty `MGLOverlay.overlayBounds` value. ([#11783](https://github.com/mapbox/mapbox-gl-native/pull/11783))
+* Fixed an issue where certain colors were being misrepresented in `NSExpression` obtained from `MGLStyleLayer` getters. ([#11725](https://github.com/mapbox/mapbox-gl-native/pull/11725))
 
 ## 0.7.0 - April 19, 2018
 
diff --git a/platform/macos/docs/guides/For Style Authors.md b/platform/macos/docs/guides/For Style Authors.md
index 73c4f1105a..08385a66d9 100644
--- a/platform/macos/docs/guides/For Style Authors.md
+++ b/platform/macos/docs/guides/For Style Authors.md
@@ -318,7 +318,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `number`               | |
 `string`               | |
 `to-boolean`           | `boolValue` |
-`to-color`             | |
+`to-color`             | | `CAST(var, 'NSColor')`
 `to-number`            | `mgl_numberWithFallbackValues:` | `CAST(zipCode, 'NSNumber')`
 `to-string`            | `stringValue` | `CAST(ele, 'NSString')`
 `typeof`               | |
@@ -350,7 +350,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `upcase`               | `uppercase:` | `uppercase('Elysian Fields')`
 `rgb`                  | `+[NSColor colorWithCalibratedRed:green:blue:alpha:]` |
 `rgba`                 | `+[NSColor colorWithCalibratedRed:green:blue:alpha:]` |
-`to-rgba`              | |
+`to-rgba`              | | `CAST(noindex(var), 'NSArray')`
 `-`                    | `from:subtract:` | `2 - 1`
 `*`                    | `multiply:by:` | `1 * 2`
 `/`                    | `divide:by:` | `1 / 2`
diff --git a/platform/macos/src/NSColor+MGLAdditions.mm b/platform/macos/src/NSColor+MGLAdditions.mm
index 8c9086ccf7..c73c1a41b7 100644
--- a/platform/macos/src/NSColor+MGLAdditions.mm
+++ b/platform/macos/src/NSColor+MGLAdditions.mm
@@ -79,8 +79,14 @@
         
         components.push_back(component.doubleValue / 255.0);
     }
-    // Alpha
-    components.back() *= 255.0;
+    
+    if (components.size() < 4) {
+        components.push_back(1.0);
+    } else {
+        // Alpha
+        components.back() *= 255.0;
+    }
+    
     
     // macOS 10.12 Sierra and below uses calibrated RGB by default.
     if ([NSColor redColor].colorSpaceName == NSCalibratedRGBColorSpace) {