Tweaks to let comp[iler know that methods to raise an exception don't return.

ChangeLog

@@ -1,3 +1,14 @@
+2018-01-25  Richard Frith-Macdonald <rfm@gnu.org>
+
+	* Headers/Foundation/NSException.h:
+	* Source/NSException.m:
+	* Source/Additions/NSObject+GNUstepBase.m:
+	Mark exception raising methods with GS_NORETURN_METHOD.
+	Alter noreturn method implementations so the compiler knows
+	that they really don't return.
+	Use pragma to suppress warnings abnout noreturn methods whose
+	formal declaration says they return an id.
+
 2018-01-23  Richard Frith-Macdonald <rfm@gnu.org>
 
 	* Source/Additions/NSNumber+GNUstepBase.m:

Headers/Foundation/NSException.h

@@ -134,7 +134,8 @@ extern "C" {
  * <em>raised</em> using the -raise method.
  */
 + (void) raise: (NSString*)name
-	format: (NSString*)format,... NS_FORMAT_FUNCTION(2,3);
+	format: (NSString*)format,...
+  NS_FORMAT_FUNCTION(2,3) GS_NORETURN_METHOD;
 
 /**
  * Creates an exception with a name and a reason string using the
@@ -144,7 +145,8 @@ extern "C" {
  */
 + (void) raise: (NSString*)name
 	format: (NSString*)format
-     arguments: (va_list)argList NS_FORMAT_FUNCTION(2,0);
+     arguments: (va_list)argList
+  NS_FORMAT_FUNCTION(2,0) GS_NORETURN_METHOD;
 
 #if OS_API_VERSION(MAC_OS_X_VERSION_10_5,GS_API_LATEST) && GS_API_VERSION( 11501,GS_API_LATEST)
 /** Returns an array of the call stack return addresses at the point when
@@ -189,7 +191,7 @@ extern "C" {
  * NB. all other exception raising methods call this one, so if you
  * want to set a breakpoint when debugging, set it in this method.
  */
-- (void) raise;
+- (void) raise GS_NORETURN_METHOD;
 
 /** Returns the exception reason. */
 - (NSString*) reason;

Source/Additions/NSObject+GNUstepBase.m

@@ -31,6 +31,12 @@
 #import "GNUstepBase/NSDebug+GNUstepBase.h"
 #import "GNUstepBase/NSThread+GNUstepBase.h"
 
+/* This file contains methods which nominally return an id but in fact
+ * always rainse an exception and never return.
+ * We need to suppress the compiler warning about that.
+ */
+#pragma GCC diagnostic ignored "-Wreturn-type"
+
 /**
  * Extension methods for the NSObject class
  */
@@ -42,7 +48,7 @@
     format: @"method %@ not implemented in %@(class)",
     selector ? (id)NSStringFromSelector(selector) : (id)@"(null)",
     NSStringFromClass(self)];
-  return nil;
+  while (0) ;   // Does not return
 }
 
 - (NSComparisonResult) compare: (id)anObject
@@ -106,7 +112,7 @@
     format: @"[%@%c%@] not implemented",
     NSStringFromClass([self class]), c,
     aSel ? (id)NSStringFromSelector(aSel) : (id)@"(null)"];
-  return self;	// Not reached
+  while (0) ;   // Does not return
 }
 
 - (id) shouldNotImplement: (SEL)aSel
@@ -118,7 +124,7 @@
     format: @"[%@%c%@] should not be implemented",
     NSStringFromClass([self class]), c,
     aSel ? (id)NSStringFromSelector(aSel) : (id)@"(null)"];
-  return self;	// Not reached
+  while (0) ;   // Does not return
 }
 
 - (id) subclassResponsibility: (SEL)aSel
@@ -129,7 +135,7 @@
     format: @"[%@%c%@] should be overridden by subclass",
     NSStringFromClass([self class]), c,
     aSel ? (id)NSStringFromSelector(aSel) : (id)@"(null)"];
-  return self;	// Not reached
+  while (0) ;   // Does not return
 }
 
 @end

Source/NSException.m

@@ -1016,6 +1016,7 @@ callUncaughtHandler(id value)
   [self raise: name format: format arguments: args];
   // This probably doesn't matter, but va_end won't get called
   va_end(args);
+  while (1);    // does not return
 }
 
 + (void) raise: (NSString*)name
@@ -1028,6 +1029,7 @@ callUncaughtHandler(id value)
   reason = [NSString stringWithFormat: format arguments: argList];
   except = [self exceptionWithName: name reason: reason userInfo: nil];
   [except raise];
+  while (1);    // does not return
 }
 
 /* For OSX compatibility -init returns nil.
@@ -1184,6 +1186,7 @@ callUncaughtHandler(id value)
     }
 }
 #endif
+  while (1);    // does not return
 }
 
 - (NSString*) name