Embrace the swift-syntax notion of Fix-Its as separate notes.

The swift-syntax diagnostic system always treats Fix-Its as separate
notes, which are never attached to the primary diagnostic. Embrace this
module in the mapping over to the existing C++ diagnostic engine.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/Diagnostics.swift

@@ -91,47 +91,34 @@ func emitDiagnostic(
   diagnostic: Diagnostic,
   messageSuffix: String? = nil
 ) {
-  // Determine the set of note IDs.
-  let knownNoteIDs: Set<MessageID> = .init(
-    diagnostic.notes.map { $0.noteMessage.fixItID }
-  )
-
-  // Collect all of the Fix-It changes based on their Fix-It ID.
-  var fixItChangesByID: [MessageID : [FixIt.Change]] = [:]
-  for fixIt in diagnostic.fixIts {
-    let id = knownNoteIDs.contains(fixIt.message.fixItID)
-        ? fixIt.message.fixItID
-        : diagnostic.diagnosticID
-    fixItChangesByID[id, default: []]
-      .append(contentsOf: fixIt.changes.changes)
-  }
-
   // Emit the main diagnostic
   emitDiagnosticParts(
     diagEnginePtr: diagEnginePtr,
     sourceFileBuffer: sourceFileBuffer,
     message: diagnostic.diagMessage.message + (messageSuffix ?? ""),
     severity: diagnostic.diagMessage.severity,
     position: diagnostic.position,
-    highlights: diagnostic.highlights,
-    fixItChanges: fixItChangesByID[diagnostic.diagnosticID] ?? []
+    highlights: diagnostic.highlights
   )
 
-  fixItChangesByID.removeValue(forKey: diagnostic.diagnosticID)
+  // Emit Fix-Its.
+  for fixIt in diagnostic.fixIts {
+    emitDiagnosticParts(
+        diagEnginePtr: diagEnginePtr,
+        sourceFileBuffer: sourceFileBuffer,
+        message: fixIt.message.message,
+        severity: .note, position: diagnostic.position,
+        fixItChanges: fixIt.changes.changes
+    )
+  }
 
   // Emit any notes as follow-ons.
   for note in diagnostic.notes {
     emitDiagnosticParts(
       diagEnginePtr: diagEnginePtr,
       sourceFileBuffer: sourceFileBuffer,
       message: note.message,
-      severity: .note, position: note.position,
-      fixItChanges: fixItChangesByID[note.noteMessage.fixItID] ?? []
+      severity: .note, position: note.position
     )
-
-    fixItChangesByID.removeValue(forKey: note.noteMessage.fixItID)
   }
-
-  // All Fix-Its must have been removed by the code above.
-  assert(fixItChangesByID.isEmpty)
 }

test/Macros/macro_expand.swift

@@ -57,8 +57,10 @@ struct OnlyAdds {
 func testAddBlocker(a: Int, b: Int, c: Int, oa: OnlyAdds) {
   _ = #addBlocker(a * b * c)
 #if TEST_DIAGNOSTICS
-  _ = #addBlocker(a + b * c) // expected-error{{blocked an add; did you mean to subtract? (from macro 'addBlocker')}}{{21-22=-}}
-  _ = #addBlocker(oa + oa) // expected-error{{blocked an add; did you mean to subtract? (from macro 'addBlocker')}}{{22-23=-}}
-      // expected-note@-1{{in expansion of macro 'addBlocker' here}}
+  _ = #addBlocker(a + b * c) // expected-error{{blocked an add; did you mean to subtract? (from macro 'addBlocker')}}
+  // expected-note@-1{{use '-'}}{{21-22=-}}
+  _ = #addBlocker(oa + oa) // expected-error{{blocked an add; did you mean to subtract? (from macro 'addBlocker')}}
+  // expected-note@-1{{in expansion of macro 'addBlocker' here}}
+  // expected-note@-2{{use '-'}}{{22-23=-}}
 #endif
 }

test/Parse/new_parser_diagnostics.swift

@@ -5,4 +5,5 @@
 // REQUIRES: asserts
 
 _ = [(Int) -> async throws Int]()
-// expected-error@-1{{'async throws' may only occur before '->'}}{{15-21=}} {{21-28=}} {{20-21= }} {{12-12=async }} {{12-12=throws }}
+// expected-error@-1{{'async throws' may only occur before '->'}}
+// expected-note@-2{{move 'async throws' in front of '->'}}{{15-21=}} {{21-28=}} {{20-21= }} {{12-12=async }} {{12-12=throws }}