[Sema][test] Add SR-13899 test cases

Author: LucianoPAlmeida

lib/Sema/CSDiagnostics.cpp

@@ -1075,7 +1075,7 @@ bool MissingExplicitConversionFailure::diagnoseAsError() {
     } else {
       // Emit error diagnostic.
       emitDiagnostic(diag::cannot_coerce_to_type, fromType, toType);
-      // Emit and return note suggesting as! where the fixit will be placed.
+      // Emit and return note suggesting as! where the fix-it will be placed.
       return emitDiagnostic(diag::missing_forced_downcast);
     }
   };

test/expr/cast/as_coerce.swift

@@ -141,3 +141,16 @@ _ = sr6022 as! AnyObject // expected-warning {{forced cast from '() -> Any' to '
 _ = sr6022 as? AnyObject // expected-warning {{conditional cast from '() -> Any' to 'AnyObject' always succeeds}}
 _ = sr6022_1 as! Any // expected-warning {{forced cast from '() -> ()' to 'Any' always succeeds; did you mean to use 'as'?}}
 _ = sr6022_1 as? Any // expected-warning {{conditional cast from '() -> ()' to 'Any' always succeeds}}
+
+// SR-13899
+let any: Any = 1
+if let int = any as Int { // expected-error {{'Any' is not convertible to 'Int'}}
+// expected-note@-1 {{did you mean to use 'as?' to conditionally downcast?}} {{18-20=as?}}
+}
+
+let _ = any as Int // expected-error {{'Any' is not convertible to 'Int'}}
+// expected-note@-1 {{did you mean to use 'as!' to force downcast?}} {{13-15=as!}}
+let _: Int = any as Int // expected-error {{'Any' is not convertible to 'Int'}}
+// expected-note@-1 {{did you mean to use 'as!' to force downcast?}} {{18-20=as!}}
+let _: Int? = any as Int // expected-error {{'Any' is not convertible to 'Int'}}
+// expected-note@-1 {{did you mean to use 'as?' to conditionally downcast?}} {{19-21=as?}}