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, 98 insertions, 151 deletions

diff --git a/platform/darwin/src/MGLFillStyleLayer.h b/platform/darwin/src/MGLFillStyleLayer.h
index e385256aae..5caab91b45 100644
--- a/platform/darwin/src/MGLFillStyleLayer.h
+++ b/platform/darwin/src/MGLFillStyleLayer.h
@@ -2,7 +2,6 @@
 // Edit platform/darwin/scripts/generate-style-code.js, then run `make darwin-style-code`.
 
 #import "MGLFoundation.h"
-#import "MGLStyleValue.h"
 #import "MGLVectorStyleLayer.h"
 
 NS_ASSUME_NONNULL_BEGIN
@@ -44,7 +43,7 @@ typedef NS_ENUM(NSUInteger, MGLFillTranslationAnchor) {
  ```swift
  let layer = MGLFillStyleLayer(identifier: "parks", source: parks)
  layer.sourceLayerIdentifier = "parks"
- layer.fillColor = MGLStyleValue(rawValue: .green)
+ layer.fillColor = NSExpression(forConstantValue: UIColor.green)
  layer.predicate = NSPredicate(format: "type == %@", "national-park")
  mapView.style?.addLayer(layer)
  ```
@@ -72,81 +71,49 @@ MGL_EXPORT
 /**
  Whether or not the fill should be antialiased.
  
- The default value of this property is an `MGLStyleValue` object containing an
- `NSNumber` object containing `YES`. Set this property to `nil` to reset it to
- the default value.
+ The default value of this property is an expression that evaluates to `YES`.
+ Set this property to `nil` to reset it to the default value.
  
  This attribute corresponds to the <a
  href="https://www.mapbox.com/mapbox-gl-style-spec/#paint-fill-antialias"><code>fill-antialias</code></a>
  layout property in the Mapbox Style Specification.
  
- You can set this property to an instance of:
+ You can set this property to an expression containing any of the following:
  
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of
- `MGLInterpolationModeInterval`
+ * Constant Boolean values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Step functions applied to the `$zoomLevel` variable
+ 
+ This property does not support applying interpolation functions to the
+ `$zoomLevel` variable or applying interpolation or step functions to feature
+ attributes.
  */
-@property (nonatomic, null_resettable, getter=isFillAntialiased) MGLStyleValue<NSNumber *> *fillAntialiased;
+@property (nonatomic, null_resettable, getter=isFillAntialiased) NSExpression *fillAntialiased;
 
-@property (nonatomic, null_resettable) MGLStyleValue<NSNumber *> *fillAntialias __attribute__((unavailable("Use fillAntialiased instead.")));
+@property (nonatomic, null_resettable) NSExpression *fillAntialias __attribute__((unavailable("Use fillAntialiased instead.")));
 
-#if TARGET_OS_IPHONE
 /**
  The color of the filled part of this layer.
  
- The default value of this property is an `MGLStyleValue` object containing
+ The default value of this property is an expression that evaluates to
  `UIColor.blackColor`. Set this property to `nil` to reset it to the default
  value.
  
  This property is only applied to the style if `fillPattern` is set to `nil`.
  Otherwise, it is ignored.
  
- You can set this property to an instance of:
- 
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
- * `MGLSourceStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
-   * `MGLInterpolationModeIdentity`
- * `MGLCompositeStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
- */
-@property (nonatomic, null_resettable) MGLStyleValue<UIColor *> *fillColor;
-#else
-/**
- The color of the filled part of this layer.
- 
- The default value of this property is an `MGLStyleValue` object containing
- `NSColor.blackColor`. Set this property to `nil` to reset it to the default
- value.
- 
- This property is only applied to the style if `fillPattern` is set to `nil`.
- Otherwise, it is ignored.
+ You can set this property to an expression containing any of the following:
  
- You can set this property to an instance of:
- 
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
- * `MGLSourceStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
-   * `MGLInterpolationModeIdentity`
- * `MGLCompositeStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
+ * Constant `UIColor` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable and/or
+ feature attributes
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSColor *> *fillColor;
-#endif
+@property (nonatomic, null_resettable) NSExpression *fillColor;
 
 /**
  The transition affecting any changes to this layer’s `fillColor` property.
@@ -159,27 +126,19 @@ MGL_EXPORT
  The opacity of the entire fill layer. In contrast to the `fillColor`, this
  value will also affect the 1pt stroke around the fill, if the stroke is used.
  
- The default value of this property is an `MGLStyleValue` object containing an
- `NSNumber` object containing the float `1`. Set this property to `nil` to reset
- it to the default value.
- 
- You can set this property to an instance of:
- 
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
- * `MGLSourceStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
-   * `MGLInterpolationModeIdentity`
- * `MGLCompositeStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
+ The default value of this property is an expression that evaluates to the float
+ `1`. Set this property to `nil` to reset it to the default value.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant numeric values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable and/or
+ feature attributes
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSNumber *> *fillOpacity;
+@property (nonatomic, null_resettable) NSExpression *fillOpacity;
 
 /**
  The transition affecting any changes to this layer’s `fillOpacity` property.
@@ -188,57 +147,23 @@ MGL_EXPORT
 */
 @property (nonatomic) MGLTransition fillOpacityTransition;
 
-#if TARGET_OS_IPHONE
 /**
  The outline color of the fill. Matches the value of `fillColor` if unspecified.
  
  This property is only applied to the style if `fillPattern` is set to `nil`,
- and `fillAntialiased` is set to an `MGLStyleValue` object containing an
- `NSNumber` object containing `YES`. Otherwise, it is ignored.
- 
- You can set this property to an instance of:
- 
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
- * `MGLSourceStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
-   * `MGLInterpolationModeIdentity`
- * `MGLCompositeStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
- */
-@property (nonatomic, null_resettable) MGLStyleValue<UIColor *> *fillOutlineColor;
-#else
-/**
- The outline color of the fill. Matches the value of `fillColor` if unspecified.
+ and `fillAntialiased` is set to an expression that evaluates to `YES`.
+ Otherwise, it is ignored.
  
- This property is only applied to the style if `fillPattern` is set to `nil`,
- and `fillAntialiased` is set to an `MGLStyleValue` object containing an
- `NSNumber` object containing `YES`. Otherwise, it is ignored.
- 
- You can set this property to an instance of:
- 
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
- * `MGLSourceStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
-   * `MGLInterpolationModeIdentity`
- * `MGLCompositeStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
-   * `MGLInterpolationModeCategorical`
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant `UIColor` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable and/or
+ feature attributes
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSColor *> *fillOutlineColor;
-#endif
+@property (nonatomic, null_resettable) NSExpression *fillOutlineColor;
 
 /**
  The transition affecting any changes to this layer’s `fillOutlineColor` property.
@@ -251,13 +176,19 @@ MGL_EXPORT
  Name of image in sprite to use for drawing image fills. For seamless patterns,
  image width and height must be a factor of two (2, 4, 8, ..., 512).
  
- You can set this property to an instance of:
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant string values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Step functions applied to the `$zoomLevel` variable
  
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of
- `MGLInterpolationModeInterval`
+ This property does not support applying interpolation functions to the
+ `$zoomLevel` variable or applying interpolation or step functions to feature
+ attributes.
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSString *> *fillPattern;
+@property (nonatomic, null_resettable) NSExpression *fillPattern;
 
 /**
  The transition affecting any changes to this layer’s `fillPattern` property.
@@ -272,7 +203,7 @@ MGL_EXPORT
  
  This property is measured in points.
  
- The default value of this property is an `MGLStyleValue` object containing an
+ The default value of this property is an expression that evaluates to an
  `NSValue` object containing a `CGVector` struct set to 0 points rightward and 0
  points downward. Set this property to `nil` to reset it to the default value.
  
@@ -280,21 +211,25 @@ MGL_EXPORT
  href="https://www.mapbox.com/mapbox-gl-style-spec/#paint-fill-translate"><code>fill-translate</code></a>
  layout property in the Mapbox Style Specification.
  
- You can set this property to an instance of:
+ You can set this property to an expression containing any of the following:
  
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
+ * Constant `CGVector` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable
+ 
+ This property does not support applying interpolation or step functions to
+ feature attributes.
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSValue *> *fillTranslation;
+@property (nonatomic, null_resettable) NSExpression *fillTranslation;
 #else
 /**
  The geometry's offset.
  
  This property is measured in points.
  
- The default value of this property is an `MGLStyleValue` object containing an
+ The default value of this property is an expression that evaluates to an
  `NSValue` object containing a `CGVector` struct set to 0 points rightward and 0
  points upward. Set this property to `nil` to reset it to the default value.
  
@@ -302,14 +237,18 @@ MGL_EXPORT
  href="https://www.mapbox.com/mapbox-gl-style-spec/#paint-fill-translate"><code>fill-translate</code></a>
  layout property in the Mapbox Style Specification.
  
- You can set this property to an instance of:
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant `CGVector` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable
  
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of:
-   * `MGLInterpolationModeExponential`
-   * `MGLInterpolationModeInterval`
+ This property does not support applying interpolation or step functions to
+ feature attributes.
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSValue *> *fillTranslation;
+@property (nonatomic, null_resettable) NSExpression *fillTranslation;
 #endif
 
 /**
@@ -319,14 +258,13 @@ MGL_EXPORT
 */
 @property (nonatomic) MGLTransition fillTranslationTransition;
 
-@property (nonatomic, null_resettable) MGLStyleValue<NSValue *> *fillTranslate __attribute__((unavailable("Use fillTranslation instead.")));
+@property (nonatomic, null_resettable) NSExpression *fillTranslate __attribute__((unavailable("Use fillTranslation instead.")));
 
 /**
  Controls the frame of reference for `fillTranslation`.
  
- The default value of this property is an `MGLStyleValue` object containing an
- `NSValue` object containing `MGLFillTranslationAnchorMap`. Set this property to
- `nil` to reset it to the default value.
+ The default value of this property is an expression that evaluates to `map`.
+ Set this property to `nil` to reset it to the default value.
  
  This property is only applied to the style if `fillTranslation` is non-`nil`.
  Otherwise, it is ignored.
@@ -335,15 +273,24 @@ MGL_EXPORT
  href="https://www.mapbox.com/mapbox-gl-style-spec/#paint-fill-translate-anchor"><code>fill-translate-anchor</code></a>
  layout property in the Mapbox Style Specification.
  
- You can set this property to an instance of:
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant `MGLFillTranslationAnchor` values
+ * Any of the following constant string values:
+   * `map`: The fill is translated relative to the map.
+   * `viewport`: The fill is translated relative to the viewport.
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Step functions applied to the `$zoomLevel` variable
  
- * `MGLConstantStyleValue`
- * `MGLCameraStyleFunction` with an interpolation mode of
- `MGLInterpolationModeInterval`
+ This property does not support applying interpolation functions to the
+ `$zoomLevel` variable or applying interpolation or step functions to feature
+ attributes.
  */
-@property (nonatomic, null_resettable) MGLStyleValue<NSValue *> *fillTranslationAnchor;
+@property (nonatomic, null_resettable) NSExpression *fillTranslationAnchor;
 
-@property (nonatomic, null_resettable) MGLStyleValue<NSValue *> *fillTranslateAnchor __attribute__((unavailable("Use fillTranslationAnchor instead.")));
+@property (nonatomic, null_resettable) NSExpression *fillTranslateAnchor __attribute__((unavailable("Use fillTranslationAnchor instead.")));
 
 @end