Improve debug description of syntax nodes

This improves the description generated by the `debugDescription` function to something like the following which is easier to read IMO

```
SourceFileSyntax
├─CodeBlockItemListSyntax
│ ╰─CodeBlockItemSyntax
│   ╰─MacroExpansionExprSyntax
│     ├─pound
│     ├─identifier("stringify")
│     ├─leftParen
│     ├─TupleExprElementListSyntax
│     │ ╰─TupleExprElementSyntax
│     │   ╰─InfixOperatorExprSyntax
│     │     ├─IntegerLiteralExprSyntax
│     │     │ ╰─integerLiteral("2")
│     │     ├─BinaryOperatorExprSyntax
│     │     │ ╰─binaryOperator("+")
│     │     ╰─IntegerLiteralExprSyntax
│     │       ╰─integerLiteral("3")
│     ╰─rightParen
╰─eof
```

Since we now have this nice representation, it also removes the conformances to `CustomReflectable` (deleting 3000 lines of code :hooray:) and doing some new `CustomReflectable` hackery to make the debugger just print `debugDescription` and not try to print the node’s children itself. This way you an now do `po node` in the debugger to get the debug description from above, instead of having to do `e print(node.recursiveDescription)`

Author: ahoppen

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntax/SyntaxBaseNodesFile.swift

@@ -233,18 +233,6 @@ let syntaxBaseNodesFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         StmtSyntax("return .choices(\(choices))")
       }
     }
-
-    DeclSyntax(
-      """
-      extension \(raw: node.name): CustomReflectable {
-        /// Reconstructs the real syntax type for this type from the node's kind and
-        /// provides a mirror that reflects this type.
-        public var customMirror: Mirror {
-          return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-        }
-      }
-      """
-    )
   }
 
   try! ExtensionDeclSyntax("extension Syntax") {

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntax/SyntaxCollectionsFile.swift

@@ -418,16 +418,4 @@ let syntaxCollectionsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       )
     }
   }
-
-  for node in SYNTAX_NODES where node.isSyntaxCollection {
-    DeclSyntax(
-      """
-      extension \(raw: node.name): CustomReflectable {
-        public var customMirror: Mirror {
-          return Mirror(self, unlabeledChildren: self.map{ $0 })
-        }
-      }
-      """
-    )
-  }
 }

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntax/SyntaxNodeFile.swift

@@ -259,27 +259,6 @@ func syntaxNode(emitKind: String) -> SourceFileSyntax {
           StmtSyntax("return .layout(\(layout))")
         }
       }
-
-      try! ExtensionDeclSyntax("extension \(raw: node.name): CustomReflectable") {
-        let children = DictionaryExprSyntax {
-          for child in node.children {
-            DictionaryElementSyntax(
-              leadingTrivia: .newline,
-              keyExpression: ExprSyntax(#""\#(raw: child.swiftName)""#),
-              valueExpression: child.isOptional
-                ? ExprSyntax("\(raw: child.swiftName).map(Syntax.init)?.asProtocol(SyntaxProtocol.self) as Any")
-                : ExprSyntax("Syntax(\(raw: child.swiftName)).asProtocol(SyntaxProtocol.self)")
-            )
-          }
-        }
-        DeclSyntax(
-          """
-          public var customMirror: Mirror {
-            return Mirror(self, children: \(children))
-          }
-          """
-        )
-      }
     }
   }
 }

Sources/SwiftSyntax/Syntax.swift

@@ -104,14 +104,6 @@ public struct Syntax: SyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension Syntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: self.asProtocol(SyntaxProtocol.self))
-  }
-}
-
 extension Syntax: Identifiable {
   public typealias ID = SyntaxIdentifier
 }
@@ -157,7 +149,7 @@ public extension SyntaxHashable {
 /// protocol to provide common functionality for all syntax nodes.
 /// DO NOT CONFORM TO THIS PROTOCOL YOURSELF!
 public protocol SyntaxProtocol: CustomStringConvertible,
-  CustomDebugStringConvertible, TextOutputStreamable
+  CustomDebugStringConvertible, TextOutputStreamable, CustomReflectable
 {
 
   /// Retrieve the generic syntax node that is represented by this node.
@@ -565,14 +557,14 @@ public extension SyntaxProtocol {
     debugDescription()
   }
 
-  /// Same as `debugDescription` but includes all children.
-  var recursiveDescription: String {
-    debugDescription(includeChildren: true)
+  var customMirror: Mirror {
+    // Suppress printing of children when doing `po node` in the debugger.
+    // `debugDescription` already prints them in a nicer way.
+    return Mirror(self, children: [:])
   }
 
   /// Returns a summarized dump of this node.
   /// - Parameters:
-  ///   - includeChildren: Whether to also dump children, false by default.
   ///   - includeTrivia: Add trivia to each dumped node, which the default
   ///   dump skips.
   ///   - converter: The location converter for the root of the tree. Adds
@@ -582,31 +574,28 @@ public extension SyntaxProtocol {
   ///   - indentLevel: The starting indent level, 0 by default. Each level is 2
   ///   spaces.
   func debugDescription(
-    includeChildren: Bool = false,
     includeTrivia: Bool = false,
     converter: SourceLocationConverter? = nil,
     mark: SyntaxProtocol? = nil,
-    indentLevel: Int = 0
+    indentString: String = ""
   ) -> String {
     var str = ""
     debugWrite(
       to: &str,
-      includeChildren: includeChildren,
       includeTrivia: includeTrivia,
       converter: converter,
       mark: mark,
-      indentLevel: indentLevel
+      indentString: indentString
     )
     return str
   }
 
   private func debugWrite<Target: TextOutputStream>(
     to target: inout Target,
-    includeChildren: Bool,
     includeTrivia: Bool,
     converter: SourceLocationConverter? = nil,
     mark: SyntaxProtocol? = nil,
-    indentLevel: Int
+    indentString: String
   ) {
     if let mark = mark, self.id == mark.id {
       target.write("*** ")
@@ -627,11 +616,6 @@ public extension SyntaxProtocol {
     }
 
     let allChildren = children(viewMode: .all)
-    if includeChildren {
-      if !allChildren.isEmpty {
-        target.write(" children=\(allChildren.count)")
-      }
-    }
 
     if let converter = converter {
       let range = sourceRange(converter: converter)
@@ -646,21 +630,19 @@ public extension SyntaxProtocol {
       target.write(" ***")
     }
 
-    if includeChildren {
-      let childIndentLevel = indentLevel + 1
-      for (num, child) in allChildren.enumerated() {
-        target.write("\n")
-        target.write(String(repeating: " ", count: childIndentLevel * 2))
-        target.write("\(num): ")
-        child.debugWrite(
-          to: &target,
-          includeChildren: includeChildren,
-          includeTrivia: includeTrivia,
-          converter: converter,
-          mark: mark,
-          indentLevel: childIndentLevel
-        )
-      }
+    for (num, child) in allChildren.enumerated() {
+      let isLastChild = num == allChildren.count - 1
+      target.write("\n")
+      target.write(indentString)
+      target.write(isLastChild ? "╰─" : "├─")
+      let childIndentString = indentString + (isLastChild ? "  " : "│ ")
+      child.debugWrite(
+        to: &target,
+        includeTrivia: includeTrivia,
+        converter: converter,
+        mark: mark,
+        indentString: childIndentString
+      )
     }
   }
 }
@@ -763,14 +745,5 @@ extension ReversedTokenSequence: CustomReflectable {
   }
 }
 
-/// Expose `recursiveDescription` on raw nodes for debugging purposes.
-extension RawSyntaxNodeProtocol {
-  /// Print this raw syntax node including all of its children.
-  /// Intended for debugging purposes only.
-  var recursiveDescription: String {
-    return Syntax(raw: raw).recursiveDescription
-  }
-}
-
 @available(*, unavailable, message: "use 'Syntax' instead")
 public struct SyntaxNode {}

Sources/SwiftSyntax/generated/SyntaxBaseNodes.swift

@@ -149,14 +149,6 @@ public struct DeclSyntax: DeclSyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension DeclSyntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-  }
-}
-
 // MARK: - ExprSyntax
 
 /// Protocol to which all `ExprSyntax` nodes conform. Extension point to add
@@ -318,14 +310,6 @@ public struct ExprSyntax: ExprSyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension ExprSyntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-  }
-}
-
 // MARK: - PatternSyntax
 
 /// Protocol to which all `PatternSyntax` nodes conform. Extension point to add
@@ -446,14 +430,6 @@ public struct PatternSyntax: PatternSyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension PatternSyntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-  }
-}
-
 // MARK: - StmtSyntax
 
 /// Protocol to which all `StmtSyntax` nodes conform. Extension point to add
@@ -583,14 +559,6 @@ public struct StmtSyntax: StmtSyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension StmtSyntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-  }
-}
-
 // MARK: - TypeSyntax
 
 /// Protocol to which all `TypeSyntax` nodes conform. Extension point to add
@@ -721,14 +689,6 @@ public struct TypeSyntax: TypeSyntaxProtocol, SyntaxHashable {
   }
 }
 
-extension TypeSyntax: CustomReflectable {
-  /// Reconstructs the real syntax type for this type from the node's kind and
-  /// provides a mirror that reflects this type.
-  public var customMirror: Mirror {
-    return Mirror(reflecting: Syntax(self).asProtocol(SyntaxProtocol.self))
-  }
-}
-
 extension Syntax {
   public static var structure: SyntaxNodeStructure {
     return .choices([