Reimplement style values atop NSExpression (#10726)

* [ios, macos] Import headers, not implementation files

* [core] Added accessors for various expression parameters

Added missing parameter accessors to various expression operator classes, as well as a method on InterpolatorBase and Step that enumerates the stops and their values.

* [ios, macos] Silenced warning in test of error condition

* [ios, macos] Made MGLSphericalPosition boxable

* [ios, macos] Implemented array enumeration during conversion

* [ios, macos] Temporarily ignore heatmap layer type

* [ios, macos] Migrated MGLSymbolStyleLayer.text to NSExpression

MGLSymbolStyleLayer.text is now of type NSExpression instead of MGLStyleValue, as a first step toward migrating the entire layer API from style values to expressions.

Implemented conversions from NSExpression to JSON arrays and vice versa. The most common NSExpression functions are now converted into style expressions, but not all of the most common style expression operators are supported yet.

* [ios, macos] Implemented string coercion

* [ios, macos] Color literals

* [ios, macos] Null constant expressions

* [ios, macos] Convert dictionary literals

* [ios, macos] Interpolation expressions

* [ios, macos] to-boolean, to-number, get from object

* [ios, macos] Variable expressions

Implemented custom expression functions for assigning and referring to variables within the context of an expression. Variables are assigned via a “context dictionary” and applied to an subexpression that is given as another argument to the same expression. Also implemented built-in variable expressions for zoom level and heatmap density.

* [ios, macos] Convert colors, offsets, padding in expressions to JSON objects

* [ios, macos] Expression-based style property getters

Implemented a conversion from mbgl::style::PropertyValues to Objective-C JSON objects, which are then converted to NSExpressions.

* [ios, macos] Consolidated property value–expression conversion in MGLStyleValueTransformer

* [ios, macos] Predicate and expression guide

Extracted documentation about predicates from a documentation comment in MGLVectorStyleLayer.h to a new jazzy guide. Added details about NSExpression support as well. Began updating the “For Style Authors” guide to reflect the transition from style values to expressions.

* [ios, macos] Updated style authoring guide

Updated the Information for Style Authors guide to discuss expressions instead of style functions. Included a table mapping style specification expression operators to NSExpression syntaxes.

* [ios, macos] Migrated codegen templates to expressions

* [ios, macos] Applied expression changes via codegen

Ran make darwin-style-code.

* [macos] Migrated macosapp to expressions

* [ios, macos] Updated style function guide

This guide needs to be thoroughly rewritten, but for now the example code has been migrated to expressions.

* [ios, macos] Eviscerated style function tests

* [ios, macos] Updated changelogs

* [ios] Migrated iosapp to expressions

* [ios, macos] Exposed JSON conversion methods publicly

* [ios, macos] Removed MGLStyleValue, MGLStyleFunction

1 files changed, 72 insertions, 57 deletions

diff --git a/platform/darwin/test/MGLBackgroundStyleLayerTests.mm b/platform/darwin/test/MGLBackgroundStyleLayerTests.mm
index c96a4fe7fa..e7c2982413 100644
--- a/platform/darwin/test/MGLBackgroundStyleLayerTests.mm
+++ b/platform/darwin/test/MGLBackgroundStyleLayerTests.mm
@@ -31,39 +31,44 @@
     {
         XCTAssertTrue(rawLayer->getBackgroundColor().isUndefined(),
                       @"background-color should be unset initially.");
-        MGLStyleValue<MGLColor *> *defaultStyleValue = layer.backgroundColor;
+        NSExpression *defaultExpression = layer.backgroundColor;
 
-        MGLStyleValue<MGLColor *> *constantStyleValue = [MGLStyleValue<MGLColor *> valueWithRawValue:[MGLColor redColor]];
-        layer.backgroundColor = constantStyleValue;
+        NSExpression *constantExpression = [NSExpression expressionWithFormat:@"%@", [MGLColor redColor]];
+        layer.backgroundColor = constantExpression;
         mbgl::style::PropertyValue<mbgl::Color> propertyValue = { { 1, 0, 0, 1 } };
         XCTAssertEqual(rawLayer->getBackgroundColor(), propertyValue,
-                       @"Setting backgroundColor to a constant value should update background-color.");
-        XCTAssertEqualObjects(layer.backgroundColor, constantStyleValue,
-                              @"backgroundColor should round-trip constant values.");
-
-        MGLStyleValue<MGLColor *> * functionStyleValue = [MGLStyleValue<MGLColor *> valueWithInterpolationMode:MGLInterpolationModeInterval cameraStops:@{@18: constantStyleValue} options:nil];
-        layer.backgroundColor = functionStyleValue;
-
-        mbgl::style::IntervalStops<mbgl::Color> intervalStops = { {{18, { 1, 0, 0, 1 }}} };
+                       @"Setting backgroundColor to a constant value expression should update background-color.");
+        XCTAssertEqualObjects(layer.backgroundColor, constantExpression,
+                              @"backgroundColor should round-trip constant value expressions.");
+
+        constantExpression = [NSExpression expressionWithFormat:@"%@", [MGLColor redColor]];
+        NSExpression *functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        layer.backgroundColor = functionExpression;
+
+        mbgl::style::IntervalStops<mbgl::Color> intervalStops = {{
+            { -INFINITY, { 1, 0, 0, 1 } },
+            { 18, { 1, 0, 0, 1 } },
+        }};
         propertyValue = mbgl::style::CameraFunction<mbgl::Color> { intervalStops };
         
         XCTAssertEqual(rawLayer->getBackgroundColor(), propertyValue,
-                       @"Setting backgroundColor to a camera function should update background-color.");
-        XCTAssertEqualObjects(layer.backgroundColor, functionStyleValue,
-                              @"backgroundColor should round-trip camera functions.");
+                       @"Setting backgroundColor to a camera expression should update background-color.");
+        XCTAssertEqualObjects(layer.backgroundColor, functionExpression,
+                              @"backgroundColor should round-trip camera expressions.");
 
                               
 
         layer.backgroundColor = nil;
         XCTAssertTrue(rawLayer->getBackgroundColor().isUndefined(),
                       @"Unsetting backgroundColor should return background-color to the default value.");
-        XCTAssertEqualObjects(layer.backgroundColor, defaultStyleValue,
+        XCTAssertEqualObjects(layer.backgroundColor, defaultExpression,
                               @"backgroundColor should return the default value after being unset.");
 
-        functionStyleValue = [MGLStyleValue<MGLColor *> valueWithInterpolationMode:MGLInterpolationModeIdentity sourceStops:nil attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundColor = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
-        functionStyleValue = [MGLStyleValue<MGLColor *> valueWithInterpolationMode:MGLInterpolationModeInterval compositeStops:@{@18: constantStyleValue} attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundColor = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
+        functionExpression = [NSExpression expressionForKeyPath:@"bogus"];
+        XCTAssertThrowsSpecificNamed(layer.backgroundColor = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION(bogus, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)", @{@10: functionExpression}];
+        XCTAssertThrowsSpecificNamed(layer.backgroundColor = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
         // Transition property test
         layer.backgroundColorTransition = transitionTest;
         auto toptions = rawLayer->getBackgroundColorTransition();
@@ -79,39 +84,44 @@
     {
         XCTAssertTrue(rawLayer->getBackgroundOpacity().isUndefined(),
                       @"background-opacity should be unset initially.");
-        MGLStyleValue<NSNumber *> *defaultStyleValue = layer.backgroundOpacity;
+        NSExpression *defaultExpression = layer.backgroundOpacity;
 
-        MGLStyleValue<NSNumber *> *constantStyleValue = [MGLStyleValue<NSNumber *> valueWithRawValue:@0xff];
-        layer.backgroundOpacity = constantStyleValue;
+        NSExpression *constantExpression = [NSExpression expressionWithFormat:@"0xff"];
+        layer.backgroundOpacity = constantExpression;
         mbgl::style::PropertyValue<float> propertyValue = { 0xff };
         XCTAssertEqual(rawLayer->getBackgroundOpacity(), propertyValue,
-                       @"Setting backgroundOpacity to a constant value should update background-opacity.");
-        XCTAssertEqualObjects(layer.backgroundOpacity, constantStyleValue,
-                              @"backgroundOpacity should round-trip constant values.");
-
-        MGLStyleValue<NSNumber *> * functionStyleValue = [MGLStyleValue<NSNumber *> valueWithInterpolationMode:MGLInterpolationModeInterval cameraStops:@{@18: constantStyleValue} options:nil];
-        layer.backgroundOpacity = functionStyleValue;
-
-        mbgl::style::IntervalStops<float> intervalStops = { {{18, 0xff}} };
+                       @"Setting backgroundOpacity to a constant value expression should update background-opacity.");
+        XCTAssertEqualObjects(layer.backgroundOpacity, constantExpression,
+                              @"backgroundOpacity should round-trip constant value expressions.");
+
+        constantExpression = [NSExpression expressionWithFormat:@"0xff"];
+        NSExpression *functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        layer.backgroundOpacity = functionExpression;
+
+        mbgl::style::IntervalStops<float> intervalStops = {{
+            { -INFINITY, 0xff },
+            { 18, 0xff },
+        }};
         propertyValue = mbgl::style::CameraFunction<float> { intervalStops };
         
         XCTAssertEqual(rawLayer->getBackgroundOpacity(), propertyValue,
-                       @"Setting backgroundOpacity to a camera function should update background-opacity.");
-        XCTAssertEqualObjects(layer.backgroundOpacity, functionStyleValue,
-                              @"backgroundOpacity should round-trip camera functions.");
+                       @"Setting backgroundOpacity to a camera expression should update background-opacity.");
+        XCTAssertEqualObjects(layer.backgroundOpacity, functionExpression,
+                              @"backgroundOpacity should round-trip camera expressions.");
 
                               
 
         layer.backgroundOpacity = nil;
         XCTAssertTrue(rawLayer->getBackgroundOpacity().isUndefined(),
                       @"Unsetting backgroundOpacity should return background-opacity to the default value.");
-        XCTAssertEqualObjects(layer.backgroundOpacity, defaultStyleValue,
+        XCTAssertEqualObjects(layer.backgroundOpacity, defaultExpression,
                               @"backgroundOpacity should return the default value after being unset.");
 
-        functionStyleValue = [MGLStyleValue<NSNumber *> valueWithInterpolationMode:MGLInterpolationModeIdentity sourceStops:nil attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundOpacity = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
-        functionStyleValue = [MGLStyleValue<NSNumber *> valueWithInterpolationMode:MGLInterpolationModeInterval compositeStops:@{@18: constantStyleValue} attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundOpacity = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
+        functionExpression = [NSExpression expressionForKeyPath:@"bogus"];
+        XCTAssertThrowsSpecificNamed(layer.backgroundOpacity = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION(bogus, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)", @{@10: functionExpression}];
+        XCTAssertThrowsSpecificNamed(layer.backgroundOpacity = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
         // Transition property test
         layer.backgroundOpacityTransition = transitionTest;
         auto toptions = rawLayer->getBackgroundOpacityTransition();
@@ -127,39 +137,44 @@
     {
         XCTAssertTrue(rawLayer->getBackgroundPattern().isUndefined(),
                       @"background-pattern should be unset initially.");
-        MGLStyleValue<NSString *> *defaultStyleValue = layer.backgroundPattern;
+        NSExpression *defaultExpression = layer.backgroundPattern;
 
-        MGLStyleValue<NSString *> *constantStyleValue = [MGLStyleValue<NSString *> valueWithRawValue:@"Background Pattern"];
-        layer.backgroundPattern = constantStyleValue;
+        NSExpression *constantExpression = [NSExpression expressionWithFormat:@"'Background Pattern'"];
+        layer.backgroundPattern = constantExpression;
         mbgl::style::PropertyValue<std::string> propertyValue = { "Background Pattern" };
         XCTAssertEqual(rawLayer->getBackgroundPattern(), propertyValue,
-                       @"Setting backgroundPattern to a constant value should update background-pattern.");
-        XCTAssertEqualObjects(layer.backgroundPattern, constantStyleValue,
-                              @"backgroundPattern should round-trip constant values.");
-
-        MGLStyleValue<NSString *> * functionStyleValue = [MGLStyleValue<NSString *> valueWithInterpolationMode:MGLInterpolationModeInterval cameraStops:@{@18: constantStyleValue} options:nil];
-        layer.backgroundPattern = functionStyleValue;
-
-        mbgl::style::IntervalStops<std::string> intervalStops = { {{18, "Background Pattern"}} };
+                       @"Setting backgroundPattern to a constant value expression should update background-pattern.");
+        XCTAssertEqualObjects(layer.backgroundPattern, constantExpression,
+                              @"backgroundPattern should round-trip constant value expressions.");
+
+        constantExpression = [NSExpression expressionWithFormat:@"'Background Pattern'"];
+        NSExpression *functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        layer.backgroundPattern = functionExpression;
+
+        mbgl::style::IntervalStops<std::string> intervalStops = {{
+            { -INFINITY, "Background Pattern" },
+            { 18, "Background Pattern" },
+        }};
         propertyValue = mbgl::style::CameraFunction<std::string> { intervalStops };
         
         XCTAssertEqual(rawLayer->getBackgroundPattern(), propertyValue,
-                       @"Setting backgroundPattern to a camera function should update background-pattern.");
-        XCTAssertEqualObjects(layer.backgroundPattern, functionStyleValue,
-                              @"backgroundPattern should round-trip camera functions.");
+                       @"Setting backgroundPattern to a camera expression should update background-pattern.");
+        XCTAssertEqualObjects(layer.backgroundPattern, functionExpression,
+                              @"backgroundPattern should round-trip camera expressions.");
 
                               
 
         layer.backgroundPattern = nil;
         XCTAssertTrue(rawLayer->getBackgroundPattern().isUndefined(),
                       @"Unsetting backgroundPattern should return background-pattern to the default value.");
-        XCTAssertEqualObjects(layer.backgroundPattern, defaultStyleValue,
+        XCTAssertEqualObjects(layer.backgroundPattern, defaultExpression,
                               @"backgroundPattern should return the default value after being unset.");
 
-        functionStyleValue = [MGLStyleValue<NSString *> valueWithInterpolationMode:MGLInterpolationModeIdentity sourceStops:nil attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundPattern = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
-        functionStyleValue = [MGLStyleValue<NSString *> valueWithInterpolationMode:MGLInterpolationModeInterval compositeStops:@{@18: constantStyleValue} attributeName:@"" options:nil];
-        XCTAssertThrowsSpecificNamed(layer.backgroundPattern = functionStyleValue, NSException, NSInvalidArgumentException, @"MGLStyleValue should raise an exception if it is applied to a property that cannot support it");
+        functionExpression = [NSExpression expressionForKeyPath:@"bogus"];
+        XCTAssertThrowsSpecificNamed(layer.backgroundPattern = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION(bogus, 'mgl_stepWithMinimum:stops:', %@, %@)", constantExpression, @{@18: constantExpression}];
+        functionExpression = [NSExpression expressionWithFormat:@"FUNCTION($zoomLevel, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)", @{@10: functionExpression}];
+        XCTAssertThrowsSpecificNamed(layer.backgroundPattern = functionExpression, NSException, NSInvalidArgumentException, @"MGLBackgroundLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
         // Transition property test
         layer.backgroundPatternTransition = transitionTest;
         auto toptions = rawLayer->getBackgroundPatternTransition();