SIL: Correctly unwrap one-element tuples in TypeConverter::computeLoweredRValueType()

Fixes rdar://problem/123978349.

Author: slavapestov

lib/SIL/IR/TypeLowering.cpp

@@ -3294,7 +3294,7 @@ TypeConverter::computeLoweredRValueType(TypeExpansionContext forExpansion,
                              AbstractionPattern origType)
         : TC(TC), forExpansion(forExpansion), origType(origType) {
       if (auto origEltType = origType.getVanishingTupleElementPatternType())
-        origType = *origEltType;
+        this->origType = *origEltType;
     }
 
     // AST function types are turned into SIL function types:

test/SILGen/variadic-generic-lowering.swift

@@ -0,0 +1,43 @@
+// RUN: %target-swift-emit-silgen %s -disable-availability-checking
+
+// Make sure we can lower all of these types without crashing.
+
+public struct G1<each T> {
+  public let t: (repeat each T)
+}
+
+public struct S1 {
+  public let g: G1< >
+  public let gg: G1<Int>
+  public let ggg: G1<Int, Float>
+}
+
+public struct G2<each T> {
+  public let t: (repeat (each T).Type)
+}
+
+public struct S2 {
+  public let g: G2< >
+  public let gg: G2<Int>
+  public let ggg: G2<Int, Float>
+}
+
+public struct G3<each T> {
+  public let t: (repeat (each T) -> ())
+}
+
+public struct S3 {
+  public let g: G3< >
+  public let gg: G3<Int>
+  public let ggg: G3<Int, Float>
+}
+
+public struct G4<each T> {
+  public let t: (repeat ((each T).Type) -> ())
+}
+
+public struct S4 {
+  public let g: G4< >
+  public let gg: G4<Int>
+  public let ggg: G4<Int, Float>
+}