use strings instead of substrings in associated values for ToolsVersionLoader.Error cases

`String` is a currency type in Swift. `Substring` is not.

Author: WowbaggersLiquidLunch

Sources/Commands/SwiftPackageTool.swift

@@ -489,7 +489,7 @@ extension SwiftPackageTool {
             case .set(let value):
                 guard let toolsVersion = ToolsVersion(string: value) else {
                     // FIXME: Probably lift this error defination to ToolsVersion.
-                    throw ToolsVersionLoader.Error.malformedToolsVersionSpecification(.versionSpecifier(value[...]))
+                    throw ToolsVersionLoader.Error.malformedToolsVersionSpecification(.versionSpecifier(value))
                 }
                 try writeToolsVersion(at: pkg, version: toolsVersion, fs: localFileSystem)
 

Sources/PackageLoading/ToolsVersionLoader.swift

@@ -135,11 +135,11 @@ public class ToolsVersionLoader: ToolsVersionLoaderProtocol {
             /// The version specifier is missing.
             case missingVersionSpecifier
             /// The comment marker is malformed.
-            case commentMarker(_ commentMarker: Substring)
+            case commentMarker(_ commentMarker: String)
             /// The label part of the Swift tools version specification is malformed.
-            case label(_ label: Substring)
+            case label(_ label: String)
             /// The version specifier is malformed.
-            case versionSpecifier(_ versionSpecifier: Substring)
+            case versionSpecifier(_ versionSpecifier: String)
         }
 
         /// Details of backward-incompatible contents with Swift tools version ≤ 5.3.
@@ -339,11 +339,11 @@ public class ToolsVersionLoader: ToolsVersionLoaderProtocol {
 
         guard toolsVersionSpecificationComponents.everythingUpToVersionSpecifierIsWellFormed else {
             if commentMarker != "//" {
-                throw Error.malformedToolsVersionSpecification(.commentMarker(commentMarker))
+                throw Error.malformedToolsVersionSpecification(.commentMarker(String(commentMarker)))
             }
 
             if label.lowercased() != "swift-tools-version:" {
-                throw Error.malformedToolsVersionSpecification(.label(label))
+                throw Error.malformedToolsVersionSpecification(.label(String(label)))
             }
 
             // The above If-statements should have covered all possible malformations in Swift tools version specification up to the version specifier.
@@ -352,7 +352,7 @@ public class ToolsVersionLoader: ToolsVersionLoaderProtocol {
         }
 
         guard let version = ToolsVersion(string: String(versionSpecifier)) else {
-            throw Error.malformedToolsVersionSpecification(.versionSpecifier(versionSpecifier))
+            throw Error.malformedToolsVersionSpecification(.versionSpecifier(String(versionSpecifier)))
         }
 
         guard version > .v5_3 || manifestComponents.isCompatibleWithPreSwift5_3_1 else {