[PlaygroundLogger] Introduced LogPolicy, with support for capping the number of children logged.

The defaults are to log up to the first 10,000 children of "aggregates" (i.e. classes, structs, etc.) and up to the first 80 + last 20 of "containers" (i.e. arrays, dictionaries, sets, etc.).
This matches the behavior of the legacy PlaygroundLogger.
This commit includes introducing new tests that these policies are applied correctly.

Author: cwakamo

PlaygroundLogger/PlaygroundLogger.xcodeproj/project.pbxproj

@@ -74,6 +74,10 @@
 		5E2756941FCF9CB000B69C83 /* SpriteKitOpaqueLoggable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E2756931FCF9CB000B69C83 /* SpriteKitOpaqueLoggable.swift */; };
 		5E4AF1AD1FDDBDE400B7C9D9 /* Unimplemented.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E4AF1AC1FDDBDE400B7C9D9 /* Unimplemented.swift */; };
 		5E4AF1AF1FDDC12A00B7C9D9 /* LegacyEntrypoints.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E4AF1AE1FDDC12A00B7C9D9 /* LegacyEntrypoints.swift */; };
+		5E5D77802040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5D777F2040BD7D00EBC3A9 /* LogPolicyTests.swift */; };
+		5E5D77812040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5D777F2040BD7D00EBC3A9 /* LogPolicyTests.swift */; };
+		5E5D77822040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5D777F2040BD7D00EBC3A9 /* LogPolicyTests.swift */; };
+		5E5F600B20409D4E007EF0A8 /* LogPolicy.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5F600A20409D4E007EF0A8 /* LogPolicy.swift */; };
 		5E5FE50B202D13C800E28C3C /* PGLConcurrentMap.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5FE50A202D13C800E28C3C /* PGLConcurrentMap.swift */; };
 		5ECE8F911FFCD2A70034D9BC /* LegacyPlaygroundLoggerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5ECE8F901FFCD2A70034D9BC /* LegacyPlaygroundLoggerTests.swift */; };
 		5EE3867420352F3200D625F0 /* CGFloat+CustomOpaqueLoggable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5EE3867320352F3200D625F0 /* CGFloat+CustomOpaqueLoggable.swift */; };
@@ -238,6 +242,8 @@
 		5E2756931FCF9CB000B69C83 /* SpriteKitOpaqueLoggable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SpriteKitOpaqueLoggable.swift; sourceTree = "<group>"; };
 		5E4AF1AC1FDDBDE400B7C9D9 /* Unimplemented.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Unimplemented.swift; sourceTree = "<group>"; };
 		5E4AF1AE1FDDC12A00B7C9D9 /* LegacyEntrypoints.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LegacyEntrypoints.swift; sourceTree = "<group>"; };
+		5E5D777F2040BD7D00EBC3A9 /* LogPolicyTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LogPolicyTests.swift; sourceTree = "<group>"; };
+		5E5F600A20409D4E007EF0A8 /* LogPolicy.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LogPolicy.swift; sourceTree = "<group>"; };
 		5E5FE50A202D13C800E28C3C /* PGLConcurrentMap.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PGLConcurrentMap.swift; sourceTree = "<group>"; };
 		5ECE8F901FFCD2A70034D9BC /* LegacyPlaygroundLoggerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LegacyPlaygroundLoggerTests.swift; sourceTree = "<group>"; };
 		5EE3867320352F3200D625F0 /* CGFloat+CustomOpaqueLoggable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "CGFloat+CustomOpaqueLoggable.swift"; sourceTree = "<group>"; };
@@ -345,6 +351,7 @@
 				5E2755D61FB682DE00B69C83 /* LogEntry+Encoding.swift */,
 				5E2755D01FB6619800B69C83 /* LogPacket.swift */,
 				5E2755D41FB6807F00B69C83 /* LogPacket+Encoding.swift */,
+				5E5F600A20409D4E007EF0A8 /* LogPolicy.swift */,
 				5E2755D21FB672DC00B69C83 /* SendData.swift */,
 				5E184714202BB72700F01AD1 /* TypeName.swift */,
 				5E27561B1FC4854C00B69C83 /* Opaque Representations */,
@@ -359,6 +366,7 @@
 		5E2646341FB64876002DC6B6 /* PlaygroundLoggerTests */ = {
 			isa = PBXGroup;
 			children = (
+				5E5D777F2040BD7D00EBC3A9 /* LogPolicyTests.swift */,
 				5ECE8F901FFCD2A70034D9BC /* LegacyPlaygroundLoggerTests.swift */,
 			);
 			path = PlaygroundLoggerTests;
@@ -892,6 +900,7 @@
 				5E2756821FCF439D00B69C83 /* NSImage+CustomOpaqueLoggable.swift in Sources */,
 				5E2755D91FB6836800B69C83 /* LogEncoder.swift in Sources */,
 				5E184715202BB72700F01AD1 /* TypeName.swift in Sources */,
+				5E5F600B20409D4E007EF0A8 /* LogPolicy.swift in Sources */,
 				5E2756791FCF3D3200B69C83 /* CIImage+CustomOpaqueLoggable.swift in Sources */,
 				5E2756871FCF451900B69C83 /* UIBezierPath+CustomOpaqueLoggable.swift in Sources */,
 				5E2756841FCF43DD00B69C83 /* NSView+CustomOpaqueLoggable.swift in Sources */,
@@ -917,6 +926,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				5E5D77802040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */,
 				5ECE8F911FFCD2A70034D9BC /* LegacyPlaygroundLoggerTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -925,6 +935,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				5E5D77812040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */,
 				5EFE9193203F6CF900E21BAA /* LegacyPlaygroundLoggerTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -951,6 +962,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				5E5D77822040BD7D00EBC3A9 /* LogPolicyTests.swift in Sources */,
 				5EFE91D7203F6F8100E21BAA /* LegacyPlaygroundLoggerTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;

PlaygroundLogger/PlaygroundLogger/LegacySupport/LegacyEntrypoints.swift

@@ -36,7 +36,7 @@ fileprivate func legacySendDataStub(_: NSData) -> Void {
 
 @_silgen_name("playground_log_hidden")
 public func legacyLog<T>(instance: T, name: String, id: Int, startLine: Int, endLine: Int, startColumn: Int, endColumn: Int) -> AnyObject {
-    let packet = LogPacket(describingResult: instance, named: name, startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn)
+    let packet = LogPacket(describingResult: instance, named: name, withPolicy: .default, startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn)
 
     let data = packet.encode()
 

PlaygroundLogger/PlaygroundLogger/LogEntry+Reflection.swift

@@ -20,11 +20,11 @@ fileprivate class DebugQuickLookObjectHook: NSObject {
 fileprivate let emptyNameString = ""
 
 extension LogEntry {
-    init(describing instance: Any, name: String? = nil) {
-        self = .init(describing: instance, name: name ?? emptyNameString, typeName: nil, summary: nil)
+    init(describing instance: Any, name: String? = nil, policy: LogPolicy) {
+        self = .init(describing: instance, name: name ?? emptyNameString, typeName: nil, summary: nil, policy: policy)
     }
 
-    private init(describing instance: Any, name: String, typeName passedInTypeName: String?, summary passedInSummary: String?) {
+    private init(describing instance: Any, name: String, typeName passedInTypeName: String?, summary passedInSummary: String?, policy: LogPolicy) {
         // TODO: need to handle optionals better (e.g. implicitly unwrap optionality, I think)
 
         // Returns either the passed-in type name/summary or the type name/summary of `instance`.
@@ -47,7 +47,7 @@ extension LogEntry {
 
         // If a type implements the `debugQuickLookObject()` Objective-C method, then get their debug quick look object and use that for logging (by passing it back through this initializer).
         else if let debugQuickLookObjectMethod = (instance as AnyObject).debugQuickLookObject, let debugQuickLookObject = debugQuickLookObjectMethod() {
-            self = .init(describing: debugQuickLookObject, name: name, typeName: typeName, summary: nil)
+            self = .init(describing: debugQuickLookObject, name: name, typeName: typeName, summary: nil, policy: policy)
         }
 
         // Otherwise, first check if this is an interesting CF type before logging structure.
@@ -68,11 +68,11 @@ extension LogEntry {
 
                 if mirror.displayStyle == .optional && mirror.children.count == 1 {
                     // If the mirror displays as an Optional and has exactly one child, then we want to unwrap the optionality and generate a log entry for the child.
-                    self = .init(describing: mirror.children.first!.value, name: name, typeName: typeName, summary: nil)
+                    self = .init(describing: mirror.children.first!.value, name: name, typeName: typeName, summary: nil, policy: policy)
                 }
                 else {
                     // Otherwise, we want to generate a log entry with the structure from the mirror.
-                    self = .init(structureFrom: mirror, name: name, typeName: typeName, summary: summary)
+                    self = .init(structureFrom: mirror, name: name, typeName: typeName, summary: summary, policy: policy)
                 }
             }
         }
@@ -83,31 +83,14 @@ extension LogEntry {
         self = .opaque(name: name, typeName: typeName, summary: summary, preferBriefSummary: false, representation: playgroundQuickLook.opaqueRepresentation)
     }
 
-    private static let superclassLogEntryName = "super"
+    fileprivate static let superclassLogEntryName = "super"
 
-    private init(structureFrom mirror: Mirror, name: String, typeName: String, summary: String) {
-        let totalChildrenCount: Int
-        var childEntries: [LogEntry] = []
-        
-        // If our Mirror has a superclassMirror, then we need to include that as the first "child" (and include it in the total children count).
-        if let superclassMirror = mirror.superclassMirror {
-            let superclassTypeName = normalizedName(of: superclassMirror.subjectType)
-            childEntries.append(LogEntry(structureFrom: superclassMirror, name: LogEntry.superclassLogEntryName, typeName: superclassTypeName, summary: superclassTypeName))
-            
-            totalChildrenCount = Int(mirror.children.count) + 1
-        }
-        else {
-            totalChildrenCount = Int(mirror.children.count)
-        }
-        
-        // Next, we need to generate log entries for all of the "real" children of this mirror.
-        childEntries += mirror.children.map { LogEntry(describing: $0.value, name: $0.label) }
-        
+    fileprivate init(structureFrom mirror: Mirror, name: String, typeName: String, summary: String, policy: LogPolicy) {
         self = .structured(name: name,
                            typeName: typeName,
                            summary: summary,
-                           totalChildrenCount: totalChildrenCount,
-                           children: childEntries,
+                           totalChildrenCount: mirror.totalChildCount,
+                           children: mirror.childEntries(using: policy),
                            disposition: .init(displayStyle: mirror.displayStyle)
         )
     }
@@ -140,3 +123,88 @@ extension LogEntry.StructuredDisposition {
         }
     }
 }
+
+extension Mirror {
+    fileprivate var totalChildCount: Int {
+        if superclassMirror != nil {
+            return Int(children.count) + 1
+        }
+        else {
+            return Int(children.count)
+        }
+    }
+
+    fileprivate func childEntries(using policy: LogPolicy) -> [LogEntry] {
+        let childPolicy: LogPolicy.ChildPolicy = {
+            switch self.displayStyle ?? .struct {
+            case .class, .struct, .tuple, .enum:
+                return policy.aggregateChildPolicy
+            case .optional, .collection, .dictionary, .set:
+                return policy.containerChildPolicy
+            }
+        }()
+
+        func logEntry(forChild child: Mirror.Child) -> LogEntry {
+            return LogEntry(describing: child.value, name: child.label, policy: policy)
+        }
+
+        func logEntriesForAllChildren() -> [LogEntry] {
+            let childEntries = children.map(logEntry(forChild:))
+            if let superclassMirror = superclassMirror {
+                return [superclassMirror.logEntry(named: LogEntry.superclassLogEntryName, usingPolicy: policy)] + childEntries
+            }
+            else {
+                return childEntries
+            }
+        }
+
+        func logEntries(forFirstChildren count: Int) -> [LogEntry] {
+            let numberOfChildren: Int
+            let superclassEntries: [LogEntry]
+            if let superclassMirror = superclassMirror {
+                superclassEntries = [superclassMirror.logEntry(named: LogEntry.superclassLogEntryName, usingPolicy: policy)]
+                numberOfChildren = count - 1
+            }
+            else {
+                superclassEntries = []
+                numberOfChildren = count
+            }
+
+            let start = children.startIndex
+            let max = children.index(start, offsetBy: numberOfChildren)
+
+            return superclassEntries + children[start..<max].map(logEntry(forChild:))
+        }
+
+        func logEntries(forLastChildren count: Int) -> [LogEntry] {
+            let max = children.endIndex
+            let start = children.index(max, offsetBy: -count)
+
+            return children[start..<max].map(logEntry(forChild:))
+        }
+
+        switch childPolicy {
+        case .all:
+            return logEntriesForAllChildren()
+        case let .head(count):
+            if totalChildCount <= count {
+                return logEntriesForAllChildren()
+            }
+
+            return logEntries(forFirstChildren: count) + [LogEntry.gap]
+        case let .headTail(headCount, tailCount):
+            if totalChildCount <= headCount + tailCount {
+                return logEntriesForAllChildren()
+            }
+
+            return logEntries(forFirstChildren: headCount) + [LogEntry.gap] + logEntries(forLastChildren: tailCount)
+        case .none:
+            return []
+        }
+    }
+
+    fileprivate func logEntry(named name: String, usingPolicy policy: LogPolicy) -> LogEntry {
+        let subjectTypeName = normalizedName(of: self.subjectType)
+        return LogEntry(structureFrom: self, name: name, typeName: subjectTypeName, summary: subjectTypeName, policy: policy)
+    }
+}

PlaygroundLogger/PlaygroundLogger/LogPacket.swift

@@ -35,8 +35,8 @@ extension LogPacket {
         self.logEntry = logEntry
     }
 
-    init(describingResult result: Any, named name: String, startLine: Int, endLine: Int, startColumn: Int, endColumn: Int, threadID: String? = nil) {
-        self = .init(logEntry: LogEntry(describing: result, name: name), startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn, threadID: threadID)
+    init(describingResult result: Any, named name: String, withPolicy policy: LogPolicy, startLine: Int, endLine: Int, startColumn: Int, endColumn: Int, threadID: String? = nil) {
+        self = .init(logEntry: LogEntry(describing: result, name: name, policy: policy), startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn, threadID: threadID)
     }
 
     init(scopeEntryWithStartLine startLine: Int, endLine: Int, startColumn: Int, endColumn: Int, threadID: String? = nil) {

PlaygroundLogger/PlaygroundLogger/LogPolicy.swift

@@ -0,0 +1,42 @@
+//===--- LogPolicy.swift --------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2018 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+struct LogPolicy {
+    static let `default`: LogPolicy = LogPolicy()
+
+    enum ChildPolicy {
+        /// Indicates that all children should be logged.
+        case all
+        /// Indicates that no more than the first `count` children should be logged.
+        case head(count: Int)
+        /// Indicates that no more than the first `headCount` and last `tailCount` children should be logged.
+        case headTail(headCount: Int, tailCount: Int)
+        /// Indicates that no children should be logged.
+        case none
+    }
+
+    /// The policy for logging children of aggregates (e.g. classes, structs, enums, tuples).
+    var aggregateChildPolicy: ChildPolicy
+
+    /// The policy for logging children of containers (e.g. optionals, collections, dictionaries, sets).
+    var containerChildPolicy: ChildPolicy
+
+    /// Initializes a new `LogPolicy`.
+    ///
+    /// - parameter aggregateChildPolicy: The policy to use for logging children of aggregates. Defaults to logging no more than the first 10,000 children.
+    /// - parameter containerChildPolicy: The policy to use for logging children of collections. Defaults to logging no more than the first 80 children plus the last 20 children.
+    init(aggregateChildPolicy: ChildPolicy = .head(count: 10_000),
+         containerChildPolicy: ChildPolicy = .headTail(headCount: 80, tailCount: 20)) {
+        self.aggregateChildPolicy = aggregateChildPolicy
+        self.containerChildPolicy = containerChildPolicy
+    }
+}

PlaygroundLogger/PlaygroundLogger/LoggerEntrypoints.swift

@@ -19,7 +19,7 @@ func logResult(_ result: Any,
                endLine: Int,
                startColumn: Int,
                endColumn: Int) {
-    let packet = LogPacket(describingResult: result, named: name, startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn)
+    let packet = LogPacket(describingResult: result, named: name, withPolicy: .default, startLine: startLine, endLine: endLine, startColumn: startColumn, endColumn: endColumn)
 
     let data = packet.encode()