Make Operator, PrecedenceGroup, and OperatorTable CustomStringConvertible.

Make the string representation of the main data types be their syntactic
form. This makes it easier to inspect and reason about their values.

Author: DougGregor

Sources/SwiftOperators/Operator.swift

@@ -48,3 +48,10 @@ public struct Operator {
     self.syntax = syntax
   }
 }
+
+extension Operator: CustomStringConvertible {
+  /// The description of an operator is the source code that produces it.
+  public var description: String {
+    (syntax ?? synthesizedSyntax()).description
+  }
+}

Sources/SwiftOperators/OperatorTable.swift

@@ -97,3 +97,31 @@ extension OperatorTable {
     return op.precedenceGroup
   }
 }
+
+extension OperatorTable: CustomStringConvertible {
+  /// The description of an operator table is the source code that produces it.
+  public var description: String {
+    var result = ""
+
+    // Turn all of the dictionary values into their string representations.
+    func add<Key: Comparable, Value: CustomStringConvertible>(
+      _ dict: [Key : Value]
+    ) {
+      if dict.isEmpty {
+        return
+      }
+
+      result.append(contentsOf: dict.sorted { $0.key < $1.key }
+        .map { $0.value.description }
+        .joined(separator: "\n"))
+
+      result += "\n"
+    }
+
+    add(precedenceGraph.precedenceGroups)
+    add(prefixOperators)
+    add(postfixOperators)
+    add(infixOperators)
+    return result
+  }
+}

Sources/SwiftOperators/PrecedenceGroup.swift

@@ -118,3 +118,10 @@ public struct PrecedenceGroup {
     self.syntax = syntax
   }
 }
+
+extension PrecedenceGroup: CustomStringConvertible {
+  /// The description of a precedence group is the source code that produces it.
+  public var description: String {
+    (syntax ?? synthesizedSyntax()).description
+  }
+}

Tests/SwiftOperatorsTest/SyntaxSynthesisTests.swift

@@ -39,4 +39,23 @@ public class SyntaxSynthesisTests: XCTestCase {
       }
       """)
   }
+
+  func testLogicalOperatorTable() {
+    let table = OperatorTable.logicalOperators
+    XCTAssertEqual(
+      table.description,
+      """
+      precedencegroup LogicalConjunctionPrecedence {
+          associativity: left
+          higherThan: LogicalDisjunctionPrecedence
+      }
+      precedencegroup LogicalDisjunctionPrecedence {
+          associativity: left
+      }
+      infix operator &&: LogicalConjunctionPrecedence
+      infix operator ||: LogicalDisjunctionPrecedence
+
+      """
+    )
+  }
 }