Fix overloaded case diagnostic (#152)

It is currently applied to code that has been rewritten, which breaks
the Xcode integration and hides the error. By delaying the rewriting, we
can restore the position of the error when it's emitted.

Author: stephencelis

Sources/CasePathsMacros/CasePathableMacro.swift

@@ -64,11 +64,7 @@ extension CasePathableMacro: MemberMacro {
     }
     let enumName = enumDecl.name.trimmed
 
-    let rewriter = SelfRewriter(selfEquivalent: enumName)
-    let memberBlock = rewriter.rewrite(enumDecl.memberBlock).cast(MemberBlockSyntax.self)
-
-    let enumCaseDecls = memberBlock
-      .members
+    let enumCaseDecls = enumDecl.memberBlock.members
       .flatMap { $0.decl.as(EnumCaseDeclSyntax.self)?.elements ?? [] }
 
     var seenCaseNames: Set<String> = []
@@ -85,8 +81,9 @@ extension CasePathableMacro: MemberMacro {
       seenCaseNames.insert(name)
     }
 
+    let rewriter = SelfRewriter(selfEquivalent: enumName)
+    let memberBlock = rewriter.rewrite(enumDecl.memberBlock).cast(MemberBlockSyntax.self)
     let casePaths = generateDeclSyntax(from: memberBlock.members, enumName: enumName)
-
     return [
       """
       public struct AllCasePaths {