Handle parent vars in async transform

If we're in a case stmt body, any DeclRefExprs
to vars bound by a pattern will actually be to an
implicit var decl that's declared for the body. We
therefore need to walk to its "parent" to get to
the var referenced by the pattern, which will have
the correct entries in the naming and placeholder
maps.

Author: hamishknight

lib/IDE/Refactoring.cpp

@@ -6140,6 +6140,14 @@ class AsyncConverter : private SourceEntityWalker {
     // TODO: Handle Result.get as well
     if (auto *DRE = dyn_cast<DeclRefExpr>(E)) {
       if (auto *D = DRE->getDecl()) {
+        // Look through to the parent var decl if we have one. This ensures we
+        // look at the var in a case stmt's pattern rather than the var that's
+        // implicitly declared in the body.
+        if (auto *VD = dyn_cast<VarDecl>(D)) {
+          if (auto *Parent = VD->getParentVarDecl())
+            D = Parent;
+        }
+
         bool AddPlaceholder = Placeholders.count(D);
         StringRef Name = newNameFor(D, false);
         if (AddPlaceholder || !Name.empty())

test/refactoring/ConvertAsync/convert_pattern.swift

@@ -293,7 +293,7 @@ func testPatterns() async throws {
   // MIXED-TUPLE-RESULT-NEXT:   let ((x, y), z) = res
   // MIXED-TUPLE-RESULT-NEXT:   let ((x1, _), z1) = res
   // MIXED-TUPLE-RESULT-NEXT:   print("a", x, y, z)
-  // MIXED-TUPLE-RESULT-NEXT:   print("b", x, z)
+  // MIXED-TUPLE-RESULT-NEXT:   print("b", x1, z1)
   // MIXED-TUPLE-RESULT-NEXT: } catch let err {
   // MIXED-TUPLE-RESULT-NEXT:   print("oh no")
   // MIXED-TUPLE-RESULT-NEXT:   print("oh no again")