[Constraint solver] Make sure to reflect pattern updates after application.

Author: DougGregor

lib/Sema/TypeCheckConstraints.cpp

@@ -2153,8 +2153,8 @@ TypeChecker::typeCheckExpression(
     performSyntacticExprDiagnostics(result, dc, isExprStmt);
   }
 
-  target.setExpr(result);
-  return target;
+  resultTarget->setExpr(result);
+  return *resultTarget;
 }
 
 Type TypeChecker::typeCheckParameterDefault(Expr *&defaultValue,
@@ -2422,6 +2422,7 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
 
   if (resultTarget) {
     initializer = resultTarget->getAsExpr();
+    pattern = resultTarget->getInitializationPattern();
     return false;
   }
 

test/stmt/statements.swift

@@ -555,7 +555,6 @@ func testThrowNil() throws {
 // condition may have contained a SequenceExpr.
 func r23684220(_ b: Any) {
   if let _ = b ?? b {} // expected-error {{initializer for conditional binding must have Optional type, not 'Any'}}
-  // expected-warning@-1 {{left side of nil coalescing operator '??' has non-optional type 'Any', so the right side is never used}}
 }