Fix <rdar://problem/23700031> QoI: Terrible diagnostic in tuple assignment

lattner · lattner · commit c7c180f8d82e · 2015-11-30T20:54:14.000-08:00
When inferring a contextual type for the input expression to an assignment, use getRValueType() to strip lvalues from tuple types in recursive positions, this allows us to produce a sensible diagnostic of: error: binary operator '%' cannot be applied to two 'T' operands instead of: error: cannot assign value of type 'T' to type '@lvalue _' because we don't have a weird lvalue type in the way.
diff --git a/lib/Sema/CSDiag.cpp b/lib/Sema/CSDiag.cpp
@@ -3855,7 +3855,7 @@ bool FailureDiagnosis::visitAssignExpr(AssignExpr *assignExpr) {
 
   // If the source type is already an error type, we've already posted an error.
   auto srcExpr = typeCheckChildIndependently(assignExpr->getSrc(),
-                                     destType->getLValueOrInOutObjectType(),
+                                             destType->getRValueType(),
                                              CTP_AssignSource);
   if (!srcExpr) return true;
   return false;
diff --git a/test/Constraints/tuple.swift b/test/Constraints/tuple.swift
@@ -141,3 +141,14 @@ variadicWithTrailingClosure(y: 0, fn: +)
 variadicWithTrailingClosure(1, 2, 3, fn: +)
 variadicWithTrailingClosure(1, fn: +)
 variadicWithTrailingClosure(fn: +)
+
+
+// <rdar://problem/23700031> QoI: Terrible diagnostic in tuple assignment
+func gcd_23700031<T>(a: T, b: T) {
+  var a = a
+  var b = b
+  (a, b) = (b, a % b)  // expected-error {{binary operator '%' cannot be applied to two 'T' operands}}
+  // expected-note @-1 {{overloads for '%' exist with these partially matching parameter lists: (UInt8, UInt8), (Int8, Int8), (UInt16, UInt16), (Int16, Int16), (UInt32, UInt32), (Int32, Int32), (UInt64, UInt64), (Int64, Int64), (UInt, UInt), (Int, Int), (Float, Float)}}
+}
+
+
