Merge pull request #69684 from tbkka/tbkka-better-unexpected-nullable-message

Clarify the error we emit when we see an unexpected null pointer

Author: tbkka

stdlib/public/runtime/DynamicCast.cpp

@@ -126,9 +126,9 @@ static HeapObject * getNonNullSrcObject(OpaqueValue *srcValue,
 
   std::string srcTypeName = nameForMetadata(srcType);
   std::string destTypeName = nameForMetadata(destType);
-  const char * const msg = "Found unexpected null pointer value"
-                    " while trying to cast value of type '%s' (%p)"
-                    " to '%s' (%p)%s\n";
+  const char * const msg = "Found a null pointer in a value of type '%s' (%p)."
+                    " Non-Optional values are not allowed to hold null pointers."
+                    " (Detected while casting to '%s' (%p))%s\n";
   if (runtime::bincompat::useLegacyPermissiveObjCNullSemanticsInCasting()) {
     // In backwards compatibility mode, this code will warn and return the null
     // reference anyway: If you examine the calls to the function, you'll see

test/Casting/CastTraps.swift.gyb

@@ -107,9 +107,9 @@ CastTrapsTestSuite.test("${t1}__${t2}")
 protocol P2 {}
 if #available(SwiftStdlib 5.5, *) {
 CastTrapsTestSuite.test("Unexpected null")
-  .crashOutputMatches("Found unexpected null pointer value while trying to cast value of type '")
+  .crashOutputMatches("Found a null pointer in a value of type '")
   .crashOutputMatches("Foo'")
-  .crashOutputMatches(" to '")
+  .crashOutputMatches("(Detected while casting to '")
   .crashOutputMatches("P2'")
   .code
 {
@@ -127,9 +127,8 @@ CastTrapsTestSuite.test("Unexpected null")
 #if _runtime(_ObjC)
 if #available(SwiftStdlib 5.5, *) {
 CastTrapsTestSuite.test("Unexpected Obj-C null")
-  .crashOutputMatches("Found unexpected null pointer value while trying to cast value of type '")
-  .crashOutputMatches("NSObject'")
-  .crashOutputMatches(" to '")
+  .crashOutputMatches("Found a null pointer in a value of type 'NSObject'")
+  .crashOutputMatches("(Detected while casting to '")
   .crashOutputMatches("P2'")
   .code
 {