Check that there are no duplicate code completion results

Code completion shouldn’t return the same result twice.

rdar://92081219

Author: ahoppen

SourceKitStressTester/Sources/Common/Message.swift

@@ -76,9 +76,14 @@ public enum SourceKitError: Error {
   }
 }
 
-public enum SourceKitErrorReason: String, Codable {
-  case errorResponse, errorTypeInResponse, errorDeserializingSyntaxTree,
-       sourceAndSyntaxTreeMismatch, missingExpectedResult, errorWritingModule
+public enum SourceKitErrorReason: Codable {
+  case errorResponse
+  case errorTypeInResponse
+  case errorDeserializingSyntaxTree
+  case sourceAndSyntaxTreeMismatch
+  case missingExpectedResult
+  case duplicateResult(name: String)
+  case errorWritingModule
 }
 
 public enum RequestInfo {
@@ -477,6 +482,8 @@ extension SourceKitErrorReason: CustomStringConvertible {
       return "SourceKit returned a syntax tree that doesn't match the expected source"
     case .missingExpectedResult:
       return "SourceKit returned a response that didn't contain the expected result"
+    case .duplicateResult(name: let name):
+      return "SourceKit returned a response that contained the result '\(name)' twice"
     case .errorWritingModule:
       return "Error while writing out module"
     }

SourceKitStressTester/Sources/StressTester/SourceKitDocument.swift

@@ -427,19 +427,31 @@ class SourceKitDocument {
   private func checkExpectedCompletionResult(_ expected: ExpectedResult, in response: SourceKitdResponse, info: RequestInfo) throws {
     let matcher = CompletionMatcher(for: expected)
     var found = false
+    var foundDuplicate: String? = nil
+    var seenResults = Set<String>()
     response.value.getArray(.key_Results).enumerate { (_, item) -> Bool in
       let result = item.getDictionary()
       found = matcher.match(result.getString(.key_Name), ignoreArgLabels: shouldIgnoreArgs(of: expected, for: result))
+      let description = result.getString(.key_Description)
+      if foundDuplicate == nil, !seenResults.insert(description).inserted {
+        foundDuplicate = description
+      }
       return !found
     }
-    if !found {
+    lazy var truncatedResponseText = {
       // FIXME: code completion responses can be huge, truncate them for now.
       let maxSize = 25_000
       var responseText = response.description
       if responseText.count > maxSize {
         responseText = responseText.prefix(maxSize) + "[truncated]"
       }
-      throw SourceKitError.failed(.missingExpectedResult, request: info, response: responseText.trimmingCharacters(in: .newlines))
+      return responseText
+    }()
+    if !found {
+      throw SourceKitError.failed(.missingExpectedResult, request: info, response: truncatedResponseText.trimmingCharacters(in: .newlines))
+    }
+    if let foundDuplicate = foundDuplicate {
+      throw SourceKitError.failed(.duplicateResult(name: foundDuplicate), request: info, response: truncatedResponseText.trimmingCharacters(in: .newlines))
     }
   }