Improves clean Debug build time by about 30%.

Resolves issue #5123 "Charts framework takes a long time to build" (#5123) by implementing the recommendations listed at the end of the issue:
- Set `Eager Linking` build setting to `Yes` for `Charts` framework target
- Set `Enable Module Verifier` build setting to `No` for `Debug` builds
- Set `Compilation Mode` to `Incremental` for `Debug` builds
- Add `-Xfrontend -warn-long-expression-type-checking=50` (or perhaps use `100`) to `OTHER_SWIFT_FLAGS` so the Swift compiler will emit warnings for expressions that take a long time to type-check. The number after the = is the number of milliseconds threshold, above which warnings will be emitted.
- Refactored the slow type-checking hotspots identified above in `ChartAnimationEasing.swift`, breaking out expressions which are slow to type-check into separate, quicker-to-type-check expressions.

Author: drewster99

Charts.xcodeproj/project.pbxproj

@@ -3,7 +3,7 @@
 	archiveVersion = 1;
 	classes = {
 	};
-	objectVersion = 53;
+	objectVersion = 54;
 	objects = {
 
 /* Begin PBXBuildFile section */
@@ -1034,7 +1034,8 @@
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
-				ENABLE_MODULE_VERIFIER = YES;
+				EAGER_LINKING = YES;
+				ENABLE_MODULE_VERIFIER = NO;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				FRAMEWORK_VERSION = A;
 				GCC_NO_COMMON_BLOCKS = YES;
@@ -1051,12 +1052,14 @@
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu99 gnu++11";
 				MTL_ENABLE_DEBUG_INFO = YES;
+				OTHER_SWIFT_FLAGS = "-Xfrontend -warn-long-expression-type-checking=50";
 				PRODUCT_BUNDLE_IDENTIFIER = com.dcg.Charts;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;
 				SKIP_INSTALL = YES;
 				SUPPORTED_PLATFORMS = "macosx iphoneos iphonesimulator appletvos appletvsimulator";
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
+				SWIFT_COMPILATION_MODE = singlefile;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
 				TVOS_DEPLOYMENT_TARGET = 12.0;
@@ -1227,6 +1230,7 @@
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
+				EAGER_LINKING = YES;
 				ENABLE_MODULE_VERIFIER = YES;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				FRAMEWORK_VERSION = A;
@@ -1244,6 +1248,7 @@
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu99 gnu++11";
 				MTL_ENABLE_DEBUG_INFO = NO;
+				OTHER_SWIFT_FLAGS = "-Xfrontend -warn-long-expression-type-checking=50";
 				PRODUCT_BUNDLE_IDENTIFIER = com.dcg.Charts;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;

Source/Charts/Animation/ChartAnimationEasing.swift

@@ -249,7 +249,12 @@ internal struct EasingFunctions
         }
 
         position = position - 1.0
-        return Double( 0.5 * (-pow(2.0, -10.0 * position) + 2.0) )
+
+        // compute partial result so Xcode's type-checker doesn't take too long
+        let partialResult: Double = -pow(2.0, -10.0 * position) + 2.0
+
+        // took 120ms to type check before breaking out partial result, above
+        return Double( 0.5 * partialResult )
     }
 
     internal static let EaseInCirc = { (elapsed: TimeInterval, duration: TimeInterval) -> Double in
@@ -265,12 +270,17 @@ internal struct EasingFunctions
 
     internal static let EaseInOutCirc = { (elapsed: TimeInterval, duration: TimeInterval) -> Double in
         var position: TimeInterval = elapsed / (duration / 2.0)
+
+        // calculate partial result so Swift compiler doesn't lose its mind
+        let sqrtPartialResult: Double = sqrt(1.0 - position * position)
         if position < 1.0
         {
-            return Double( -0.5 * (sqrt(1.0 - position * position) - 1.0) )
+            // was 800ms to type check with inlined sqrt calculation, from above
+            return Double( -0.5 * (sqrtPartialResult - 1.0) )
         }
         position -= 2.0
-        return Double( 0.5 * (sqrt(1.0 - position * position) + 1.0) )
+        // was 1500ms to type check with inlined sqrt calculation, from above
+        return Double( 0.5 * (sqrtPartialResult + 1.0) )
     }
 
     internal static let EaseInElastic = { (elapsed: TimeInterval, duration: TimeInterval) -> Double in
@@ -328,13 +338,23 @@ internal struct EasingFunctions
             return Double( -0.5 * (pow(2.0, 10.0 * position) * sin((position * duration - s) * (2.0 * Double.pi) / p)) )
         }
         position -= 1.0
-        return Double( pow(2.0, -10.0 * position) * sin((position * duration - s) * (2.0 * Double.pi) / p) * 0.5 + 1.0 )
+
+        // Break out partial result so the Swift compiler doesn't lose its mind
+        let sinPartialResult: Double = sin((position * duration - s) * (2.0 * Double.pi) / p)
+
+        // Original expression here, with the expression above inlined, took 600ms to type check
+        return Double( pow(2.0, -10.0 * position) * sinPartialResult * 0.5 + 1.0 )
     }
 
     internal static let EaseInBack = { (elapsed: TimeInterval, duration: TimeInterval) -> Double in
         let s: TimeInterval = 1.70158
         var position: TimeInterval = elapsed / duration
-        return Double( position * position * ((s + 1.0) * position - s) )
+
+        // Break out partial result so the Swift compiler doesn't lose its mind
+        let partialResult: Double = ((s + 1.0) * position - s)
+
+        // Original expression here, with partialResult inlined, took 260ms to type check
+        return Double( position * position * partialResult )
     }
 
     internal static let EaseOutBack = { (elapsed: TimeInterval, duration: TimeInterval) -> Double in