Apply the solution to the CS before diagnosing solution fixes.

Author: gregomni

lib/Sema/CSApply.cpp

@@ -7765,6 +7765,8 @@ bool ConstraintSystem::applySolutionFixes(Expr *E, const Solution &solution) {
   llvm::SmallDenseMap<Expr *, SmallVector<const ConstraintFix *, 4>>
       fixesPerExpr;
 
+  applySolution(solution);
+
   for (auto *fix : solution.Fixes)
     fixesPerExpr[fix->getAnchor()].push_back(fix);
 

lib/Sema/CSDiag.cpp

@@ -883,7 +883,7 @@ void swift::diagnoseSubElementFailure(Expr *destExpr,
     }
   }
 
-  auto type = destExpr->getType() ?: CS.getType(destExpr);
+  auto type = destExpr->getType() ?: CS.simplifyType(CS.getType(destExpr));
   TC.diagnose(loc, unknownDiagID, type)
       .highlight(immInfo.first->getSourceRange());
 }

lib/Sema/CSDiagnostics.cpp

@@ -565,14 +565,6 @@ bool RValueTreatedAsLValueFailure::diagnose() {
       diagExpr = parens->getSubExpr();
   }
 
-  // FIXME: Needed right now to apply correct overload choices to diagExpr for
-  // use by diagnoseSubElementFailure(). Once all callers are routed through
-  // here, that function can be rewritten to take the current Solution and use
-  // it for determining chosen decl bindings instead, making this extra
-  // typecheck unnecessary.
-  getConstraintSystem().TC.typeCheckExpression(diagExpr,
-                                               getConstraintSystem().DC);
-
   diagnoseSubElementFailure(diagExpr, loc, getConstraintSystem(),
                             subElementDiagID, rvalueDiagID);
   return true;

test/expr/cast/array_iteration.swift

@@ -16,9 +16,7 @@ for view in rootView.subviews as! [View] { // expected-warning{{immutable value
   doFoo()
 }
 
-// FIXME: Diagnostic below should be "'AnyObject' is not convertible to
-// 'View'", but IUO type gets in the way of proper diagnosis.
-for view:View in rootView.subviews { // expected-error{{type 'Array<AnyObject>?' does not conform to protocol 'Sequence'}}
+for view:View in rootView.subviews { // expected-error{{'AnyObject' is not convertible to 'View'}}
   doFoo()
 }
 

test/expr/expressions.swift

@@ -614,7 +614,7 @@ func unaryOps(_ i8: inout Int8, i64: inout Int64) {
   i64 += 1
   i8 -= 1
 
-  Int64(5) += 1 // expected-error{{left side of mutating operator isn't mutable: function call returns immutable value}}
+  Int64(5) += 1 // expected-error{{left side of mutating operator has immutable type 'Int64'}}
 
   // <rdar://problem/17691565> attempt to modify a 'let' variable with ++ results in typecheck error not being able to apply ++ to Float
   let a = i8 // expected-note {{change 'let' to 'var' to make it mutable}} {{3-6=var}}

validation-test/stdlib/FixedPointDiagnostics.swift.gyb

@@ -95,7 +95,8 @@ func testMixedSignArithmetic() {
     x += Stride(1) // expected-error {{'+=' is unavailable: Please use explicit type conversions or Strideable methods for mixed-type arithmetics.}}
     x -= Stride(1) // expected-error {{'-=' is unavailable: Please use explicit type conversions or Strideable methods for mixed-type arithmetics.}}
 
-    _ = (x - x) as Stride // expected-error {{ambiguous reference to member '-'}}
+    // Terrible over-specific error, but at least disabled
+    _ = (x - x) as Stride // expected-error {{'(@lvalue ${T}, @lvalue ${T}) -> ${T}' is not convertible to '(${T}, ${T}) -> ${T}'}}
 
     //===------------------------------------------------------------------===//
     // The following errors are different because they're not being