[ConstraintSystem] Add a new fix to diagnose extraneous return(s) in result build body

Author: xedin

include/swift/Sema/CSFix.h

@@ -2023,7 +2023,8 @@ class AllowKeyPathWithoutComponents final : public ConstraintFix {
                                                ConstraintLocator *locator);
 };
 
-class IgnoreInvalidResultBuilderBody final : public ConstraintFix {
+class IgnoreInvalidResultBuilderBody : public ConstraintFix {
+protected:
   enum class ErrorInPhase {
     PreCheck,
     ConstraintGeneration,
@@ -2062,6 +2063,22 @@ class IgnoreInvalidResultBuilderBody final : public ConstraintFix {
   create(ConstraintSystem &cs, ErrorInPhase phase, ConstraintLocator *locator);
 };
 
+class IgnoreResultBuilderWithReturnStmts final
+    : public IgnoreInvalidResultBuilderBody {
+  Type BuilderType;
+
+  IgnoreResultBuilderWithReturnStmts(ConstraintSystem &cs, Type builderTy,
+                                     ConstraintLocator *locator)
+      : IgnoreInvalidResultBuilderBody(cs, ErrorInPhase::PreCheck, locator),
+        BuilderType(builderTy) {}
+
+public:
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  static IgnoreResultBuilderWithReturnStmts *
+  create(ConstraintSystem &cs, Type builderTy, ConstraintLocator *locator);
+};
+
 class SpecifyContextualTypeForNil final : public ConstraintFix {
   SpecifyContextualTypeForNil(ConstraintSystem &cs,
                               ConstraintLocator *locator)

lib/Sema/CSFix.cpp

@@ -1644,3 +1644,15 @@ AllowRefToInvalidDecl::create(ConstraintSystem &cs,
                               ConstraintLocator *locator) {
   return new (cs.getAllocator()) AllowRefToInvalidDecl(cs, locator);
 }
+
+bool IgnoreResultBuilderWithReturnStmts::diagnose(const Solution &solution,
+                                                  bool asNote) const {
+  return false;
+}
+
+IgnoreResultBuilderWithReturnStmts *
+IgnoreResultBuilderWithReturnStmts::create(ConstraintSystem &cs, Type builderTy,
+                                           ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      IgnoreResultBuilderWithReturnStmts(cs, builderTy, locator);
+}