[TypeChecker/BuilderTransform] Make sure implicit load expression updates types in AST

Can't use `ConstraintSystem::addImplicitLoadExpr` because that would
only cache types in constraint system and wouldn't propagate them to AST,
since that happens in `ExprRewritter::finalize` during regular solution
application. `TypeChecker::addImplicitLoadExpr` should be used directly
in cases like that.

Resolves: rdar://problem/58972627

Author: xedin

lib/Sema/BuilderTransform.cpp

@@ -694,8 +694,8 @@ class BuilderClosureRewriter
 
       // Load the right-hand side if needed.
       if (finalCapturedExpr->getType()->is<LValueType>()) {
-        auto &cs = solution.getConstraintSystem();
-        finalCapturedExpr = cs.addImplicitLoadExpr(finalCapturedExpr);
+        finalCapturedExpr =
+            TypeChecker::addImplicitLoadExpr(ctx, finalCapturedExpr);
       }
 
       auto assign = new (ctx) AssignExpr(
@@ -840,8 +840,7 @@ class BuilderClosureRewriter
 
         // Load the condition if needed.
         if (finalCondExpr->getType()->is<LValueType>()) {
-          auto &cs = solution.getConstraintSystem();
-          finalCondExpr = cs.addImplicitLoadExpr(finalCondExpr);
+          finalCondExpr = TypeChecker::addImplicitLoadExpr(ctx, finalCondExpr);
         }
 
         condElement.setBoolean(finalCondExpr);

lib/Sema/TypeChecker.h

@@ -1094,10 +1094,13 @@ class TypeChecker final {
   /// more complicated than simplify wrapping given root in newly created
   /// `LoadExpr`, because `ForceValueExpr` and `ParenExpr` supposed to appear
   /// only at certain positions in AST.
-  static Expr *
-  addImplicitLoadExpr(ASTContext &Context, Expr *expr,
-                      std::function<Type(Expr *)> getType,
-                      std::function<void(Expr *, Type)> setType);
+  static Expr *addImplicitLoadExpr(ASTContext &Context, Expr *expr,
+                                   std::function<Type(Expr *)> getType =
+                                       [](Expr *E) { return E->getType(); },
+                                   std::function<void(Expr *, Type)> setType =
+                                       [](Expr *E, Type type) {
+                                         E->setType(type);
+                                       });
 
   /// Determine whether the given type contains the given protocol.
   ///

validation-test/Sema/SwiftUI/rdar58972627.swift

@@ -0,0 +1,40 @@
+// RUN: %target-swift-frontend %s -target x86_64-apple-macosx10.15 -emit-sil -verify
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+import SwiftUI
+import Combine
+
+struct A: View {
+  var body: some View {
+    Spacer()
+  }
+}
+
+struct B: View {
+  var body: some View {
+    Spacer()
+  }
+}
+
+class Context: ObservableObject {
+  @State var flag: Bool
+
+  init() {
+    self.flag = false
+  }
+}
+
+struct S : View {
+  @EnvironmentObject var context: Context
+
+  var body: some View {
+    VStack {
+      if (context.flag) { // Ok (shouldn't trip SIL Verifier)
+        A()
+      } else {
+        B()
+      }
+    }
+  }
+}