preserve old formatting of Package.resolved in tools-version < 5.6 (#3931) (#3939)

motivation: We moved to JSONEncoder in 5.6 which formats JSON in a non-traditional way (add space around the field name colon), and different from previous version of SwiftPM. We can make the change tools-version dependent.

changes: user older JSON encoder when tools-version < 5.6, preserving previous format

rdar://86341850

Author: tomerd

Sources/PackageGraph/PinsStore.swift

@@ -184,7 +184,9 @@ fileprivate struct PinsStorage {
                 data = try self.encoder.encode(container)
             } else {
                 let container = try V1(pins: pins, mirrors: mirrors)
-                data = try self.encoder.encode(container)
+                let json = container.toLegacyJSON()
+                let bytes = json.toBytes(prettyPrint: true)
+                data = Data(bytes.contents)
             }
 #if !os(Windows)
             // rdar://83646952: add newline for POSIXy systems
@@ -231,8 +233,23 @@ fileprivate struct PinsStorage {
             )
         }
 
+        // backwards compatibility of JSON format
+        func toLegacyJSON() -> JSON {
+            return .init([
+                "version": self.version.toJSON(),
+                "object": self.object.toLegacyJSON()
+            ])
+        }
+
         struct Container: Codable {
             var pins: [Pin]
+
+            // backwards compatibility of JSON format
+            func toLegacyJSON() -> JSON {
+                return .init([
+                    "pins": self.pins.map { $0.toLegacyJSON() },
+                ])
+            }
         }
 
         struct Pin: Codable {
@@ -256,6 +273,15 @@ fileprivate struct PinsStorage {
                 self.repositoryURL = mirrors.originalURL(for: location) ?? location
                 self.state = try .init(pin.state)
             }
+
+            // backwards compatibility of JSON format
+            func toLegacyJSON() -> JSON {
+                return .init([
+                    "package": self.package.toJSON(),
+                    "repositoryURL": self.repositoryURL.toJSON(),
+                    "state": self.state.toLegacyJSON()
+                ])
+            }
         }
 
         struct State: Codable {
@@ -281,6 +307,15 @@ fileprivate struct PinsStorage {
                     throw StringError("invalid pin state: \(state)")
                 }
             }
+
+            // backwards compatibility of JSON format
+            func toLegacyJSON() -> JSON {
+                return .init([
+                    "revision": self.revision.toJSON(),
+                    "version": self.version.toJSON(),
+                    "branch": self.branch.toJSON()
+                ])
+            }
         }
     }