[Sema] Avoid merging type variables that can have different results in CS.

This patch avoids merging type variables inside UnresolvedMemberExpr
and those outside, because they may not always be equivalent in CS.

Resolves: SR-8385.

Author: dingobye

lib/Sema/CSGen.cpp

@@ -317,6 +317,13 @@ namespace {
         return { false, expr };
       }
 
+      // Don't walk into unresolved member expressions - we avoid merging type
+      // variables inside UnresolvedMemberExpr and those outside, since they
+      // should be allowed to behave independently in CS.
+      if (isa<UnresolvedMemberExpr>(expr)) {
+        return {false, expr };
+      }
+
       return { true, expr };
     }
 

test/Constraints/array_literal.swift

@@ -340,3 +340,19 @@ func testConditional(i: Int, s: String) {
   let _: PArray<Int> = [i, i, i]
   let _: PArray<String> = [s, s, s] // expected-error{{cannot convert value of type '[String]' to specified type 'PArray<String>'}}
 }
+
+
+// SR-8385
+enum SR8385: ExpressibleByStringLiteral {
+  case text(String)
+  init(stringLiteral value: String) {
+    self = .text(value)
+  }
+}
+
+func testSR8385() {
+  let _: [SR8385] = [SR8385("hello")]
+  let _: [SR8385] = [.text("hello")]
+  let _: [SR8385] = ["hello", SR8385.text("world")]
+  let _: [SR8385] = ["hello", .text("world")]
+}