[ios, macos] Restored OEM conditionals where available

This is the preferred syntax for simple conditionals on iOS 9 and above, because you can inline the predicate instead of wrapping it in a constant value expression, which means you can write a conditional in a single format string.

4 files changed, 66 insertions, 3 deletions

diff --git a/platform/darwin/docs/guides/For Style Authors.md.ejs b/platform/darwin/docs/guides/For Style Authors.md.ejs
index 8dd5d53ebf..45cfa105b8 100644
--- a/platform/darwin/docs/guides/For Style Authors.md.ejs
+++ b/platform/darwin/docs/guides/For Style Authors.md.ejs
@@ -354,7 +354,7 @@ In style specification | Method, function, or predicate type | Format string syn
 `>=`                   | `NSGreaterThanOrEqualToPredicateOperatorType` | `key >= value`
 `all`                  | `NSAndPredicateType` | `p0 AND … AND pn`
 `any`                  | `NSOrPredicateType` | `p0 OR … OR pn`
-`case`                 | `MGL_IF` | `MGL_IF(1 = 2, YES, 2 = 2, YES, NO)` 
+`case`                 | `+[NSExpression expressionForConditional:trueExpression:falseExpression:]` or `MGL_IF` | `TERNARY(1 = 2, YES, NO)` or `MGL_IF(1 = 2, YES, 2 = 2, YES, NO)`
 `coalesce`             | `mgl_coalesce:` | `mgl_coalesce({x, y, z})`
 `match`                | `MGL_MATCH` | `MGL_MATCH(x, 0, 'zero match', 1, 'one match', 'two match', 'default')`
 `interpolate`          | `mgl_interpolate:withCurveType:parameters:stops:` |
diff --git a/platform/darwin/docs/guides/Predicates and Expressions.md b/platform/darwin/docs/guides/Predicates and Expressions.md
index 53fe40e3aa..4abdcff492 100644
--- a/platform/darwin/docs/guides/Predicates and Expressions.md
+++ b/platform/darwin/docs/guides/Predicates and Expressions.md
@@ -199,8 +199,7 @@ Initializer parameter | Format string syntax | Description
 `mgl_coalesce:` | `mgl_coalesce({x, y, z})` | Returns the first non-`nil` value from an array of expressions.
 `MGL_LET` | `MGL_LET('age', uppercase('old'), 'name', uppercase('MacDonald'), mgl_join({$age, $name}))` | Any number of variable names interspersed with their assigned `NSExpression` values, followed by an `NSExpression` that may contain references to those variables. Compared to the `mgl_expressionWithContext:` custom function, this function takes the variable names and values inline before the expression that contains references to those variables.
 `MGL_MATCH` | `MGL_MATCH(x, 0, 'zero match', 1, 'one match', 'two match', 'default')` | Evaluates the first expression and returns the value that matches the initial condition. After the first expression condition a pair of matching/return value should be added and a default value.
-`MGL_IF` | `MGL_IF(1 = 2, YES, 2 = 2, YES, NO)` | Returns the first value that meets the condition otherwise a default value. The expression conditions should be added in pairs of conditional/return value.
-`mgl_hasProperty:properties:` | `mgl_hasProperty:properties:('x', {'x': 'value'})` | Evaluates the expression and returns true if the properties contains the passed property.
+`MGL_IF` | `MGL_IF(1 = 2, YES, 2 = 2, YES, NO)` | Returns the first value that meets the condition otherwise a default value. The expression conditions should be added in pairs of conditional/return value. Unlike `+[NSExpression expressionForConditional:trueExpression:falseExpression:]` or the `TERNARY()` syntax, this function can accept multiple “if else” conditions and is supported on iOS 8._x_ and macOS 10.10._x_; however, each conditional passed into this function must be wrapped in a constant expression.
 
 The following custom functions are also available with the
 `+[NSExpression expressionForFunction:selectorName:arguments:]` method or the
diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 765d1e9385..7fe8ce3c91 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -665,6 +665,12 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
                 }
             }
             
+            if (@available(iOS 9.0, *)) {
+                if (arguments.count == 3) {
+                    NSPredicate *conditional = [NSPredicate mgl_predicateWithJSONObject:argumentObjects.firstObject];
+                    return [NSExpression expressionForConditional:conditional trueExpression:arguments[1] falseExpression:arguments[2]];
+                }
+            }
             return [NSExpression expressionForFunction:@"MGL_IF" arguments:arguments];
         } else if ([op isEqualToString:@"match"]) {
             NSMutableArray *optionsArray = [NSMutableArray array];
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 63c8e5d2f1..bcc708e51e 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -671,6 +671,31 @@ using namespace std::string_literals;
 }
 
 - (void)testConditionalExpressionObject {
+    // This test crashes on iOS 8, which doesn't have `+[NSExpression expressionForConditional:trueExpression:falseExpression:]`.
+    // https://github.com/mapbox/mapbox-gl-native/issues/11007
+    if (@available(iOS 9.0, *)) {
+        {
+            NSPredicate *conditional = [NSPredicate predicateWithFormat:@"1 = 2"];
+            NSExpression *trueExpression = [NSExpression expressionForConstantValue:@YES];
+            NSExpression *falseExpression = [NSExpression expressionForConstantValue:@NO];
+            NSExpression *expression = [NSExpression expressionForConditional:conditional trueExpression:trueExpression falseExpression:falseExpression];
+            NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @NO];
+            XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+            XCTAssertEqualObjects([NSExpression expressionWithFormat:@"TERNARY(1 = 2, TRUE, FALSE)"].mgl_jsonExpressionObject, jsonExpression);
+            XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
+            XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        }
+        {
+            NSExpression *expression = [NSExpression expressionWithFormat:@"TERNARY(0 = 1, TRUE, TERNARY(1 = 2, TRUE, FALSE))"];
+            NSArray *jsonExpression = @[@"case", @[@"==", @0, @1], @YES, @[@"==", @1, @2], @YES, @NO];
+            XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+            XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
+            expression = [NSExpression expressionWithFormat:@"MGL_IF(%@, TRUE, %@, TRUE, FALSE)",
+                          MGLConstantExpression([NSPredicate predicateWithFormat:@"0 = 1"]),
+                          MGLConstantExpression([NSPredicate predicateWithFormat:@"1 = 2"])];
+            XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        }
+    }
     {
         NSExpression *expression = [NSExpression expressionWithFormat:@"MGL_IF(%@, %@, %@)",
                                     [NSExpression expressionWithFormat:@"%@", [NSPredicate predicateWithFormat:@"1 = 2"]],
@@ -680,6 +705,9 @@ using namespace std::string_literals;
         NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @NO];
         XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
         XCTAssertEqualObjects(compatibilityExpression.mgl_jsonExpressionObject, jsonExpression);
+        if (@available(iOS 9.0, *)) {
+            expression = [NSExpression expressionWithFormat:@"TERNARY(1 = 2, YES, NO)"];
+        }
         XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
         XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
     }
@@ -745,6 +773,36 @@ using namespace std::string_literals;
         XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
         XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
     }
+    {
+        NSExpression *expression;
+        if (@available(iOS 9.0, *)) {
+            expression = [NSExpression expressionWithFormat:@"TERNARY(key != nil, 1, 0)"];
+        } else {
+            expression = [NSExpression expressionWithFormat:@"MGL_IF(%@, 1, 0)",
+                          MGLConstantExpression([NSPredicate predicateWithFormat:@"key != nil"])];
+        }
+        NSArray *jsonExpression = @[@"case", @[@"!=", @[@"get", @"key"], [NSNull null]], @1, @0];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:@{} context:nil], @NO);
+        XCTAssertEqualObjects([expression expressionValueWithObject:@{@"key": @"🗝"} context:nil], @YES);
+    }
+    {
+        NSDictionary *dictionary = @{@"key": @"🔑"};
+        NSExpression *expression;
+        if (@available(iOS 9.0, *)) {
+            expression = [NSExpression expressionWithFormat:@"TERNARY(%@.key != nil, 1, 0)", dictionary];
+        } else {
+            NSPredicate *conditional = [NSPredicate predicateWithFormat:@"%@.key != nil", dictionary];
+            expression = [NSExpression expressionWithFormat:@"MGL_IF(%@, 1, 0)",
+                          MGLConstantExpression(conditional)];
+        }
+        NSArray *jsonExpression = @[@"case", @[@"!=", @[@"get", @"key", @[@"literal", dictionary]], [NSNull null]], @1, @0];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        // The dictionary isn’t equal enough.
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression].description, expression.description);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @YES);
+    }
 }
 
 - (void)testGenericExpressionObject {