[sourcekitd][CursorInfo] Make sure we handle the implict VarDelcs being introduced in CastStmt bodies

When CursorInfo finds a reference to a VarDecl that's implicit but has a parent
VarDecl (according to VarDecl::getParentVarDecl), act as if we found the parent
instead.

Author: Nathan Hawes

lib/IDE/SwiftSourceDocInfo.cpp

@@ -79,11 +79,19 @@ bool CursorInfoResolver::tryResolve(ValueDecl *D, TypeDecl *CtorTyRef,
   if (!D->hasName())
     return false;
 
-  if (Loc == LocToResolve) {
-    CursorInfo.setValueRef(D, CtorTyRef, ExtTyRef, IsRef, Ty, ContainerType);
-    return true;
+  if (Loc != LocToResolve)
+    return false;
+
+  if (auto *VD = dyn_cast<VarDecl>(D)) {
+    // Handle references to the implicitly generated vars in case statements
+    // matching multiple patterns
+    if (VD->isImplicit()) {
+      if (auto * Parent = VD->getParentVarDecl())
+        D = Parent;
+    }
   }
-  return false;
+  CursorInfo.setValueRef(D, CtorTyRef, ExtTyRef, IsRef, Ty, ContainerType);
+  return true;
 }
 
 bool CursorInfoResolver::tryResolve(ModuleEntity Mod, SourceLoc Loc) {

test/SourceKit/CursorInfo/cursor_vardecl_across_fallthrough.swift

@@ -0,0 +1,57 @@
+
+enum X {
+  case first(Int, String)
+  case second(Int, String)
+  case third(Int, String)
+  case fourth(Int, String)
+  case fifth(Int, String)
+}
+
+let p = X.first(3, "hello")
+
+switch p {
+  case .first(let x, let y)
+    print("foo \(x) \(y)")
+    fallthrough
+  case .second(let x, let y), .third(let x, let y):
+    print("bar \(x) \(y)")
+  default:
+    print("other")
+}
+
+// RUN: %sourcekitd-test -req=cursor -pos=13:19 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKX,CHECK1DECL %s
+// RUN: %sourcekitd-test -req=cursor -pos=14:18 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKX,CHECK1REF %s
+
+// CHECK1DECL: source.lang.swift.decl.var.local (13:19-13:20)
+// CHECK1REF: source.lang.swift.ref.var.local (13:19-13:20)
+
+// RUN: %sourcekitd-test -req=cursor -pos=16:20 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKX,CHECK2DECL %s
+// RUN: %sourcekitd-test -req=cursor -pos=16:42 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKX,CHECK2DECL2 %s
+// RUN: %sourcekitd-test -req=cursor -pos=17:18 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKX,CHECK2REF %s
+
+// CHECK2DECL: source.lang.swift.decl.var.local (16:20-16:21)
+// CHECK2DECL2: source.lang.swift.decl.var.local (16:42-16:43)
+// CHECK2REF: source.lang.swift.ref.var.local (16:20-16:21)
+
+// CHECKX: x
+// CHECKX: s:33cursor_vardecl_across_fallthrough1xL_Sivp
+// CHECKX: Int
+
+
+// RUN: %sourcekitd-test -req=cursor -pos=13:26 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKY,CHECK3DECL %s
+// RUN: %sourcekitd-test -req=cursor -pos=14:23 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKY,CHECK3REF %s
+
+// CHECK3DECL: source.lang.swift.decl.var.local (13:26-13:27)
+// CHECK3REF: source.lang.swift.ref.var.local (13:26-13:27)
+
+// RUN: %sourcekitd-test -req=cursor -pos=16:27 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKY,CHECK4DECL %s
+// RUN: %sourcekitd-test -req=cursor -pos=16:49 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKY,CHECK4DECL2 %s
+// RUN: %sourcekitd-test -req=cursor -pos=17:23 %s -- %mcp_opt %s | %FileCheck -check-prefixes=CHECKY,CHECK4REF %s
+
+// CHECK4DECL: source.lang.swift.decl.var.local (16:27-16:28)
+// CHECK4DECL2: source.lang.swift.decl.var.local (16:49-16:50)
+// CHECK4REF: source.lang.swift.ref.var.local (16:27-16:28)
+
+// CHECKY: y
+// CHECKY: s:33cursor_vardecl_across_fallthrough1yL_SSvp
+// CHECKY: String