Permit DO to raise errors again

src/boot/errors.r

@@ -138,7 +138,7 @@ Script: [
 	; !!! Temporary errors while faulty constructs are still outstanding
 	; (more informative than just saying "function doesn't take that type")
 	use-eval-for-eval:  {Use EVAL (not DO) for inline evaluation of a value}
-	use-fail-for-error: {Use FAIL (instead of THROW or DO) to trigger ERROR!}
+	use-fail-for-error: [{Use FAIL (not THROW or DO) to raise} :arg1]
 	use-split-simple:   {Use SPLIT (instead of PARSE) for "simple" parsing}
 
 	limited-fail-input: {FAIL requires complex expressions to be in a PAREN!}

src/boot/sysobj.r

@@ -144,7 +144,6 @@ options: context [  ; Options supplied to REBOL during startup
 	exit-functions-only: false
 	broken-case-semantics: false
 	do-runs-functions: false
-	do-raises-errors: false
 	datatype-word-strict: false
 	group-not-paren: false ;; bias the default to PAREN! vs GROUP! (for now...)
 	refinements-true: false

src/core/n-control.c

@@ -677,11 +677,11 @@ enum {
 		// trying to use it to trigger errors, because if THROW just didn't
 		// take errors in the spec it wouldn't guide what *to* use.
 		//
-		raise Error_0(RE_USE_FAIL_FOR_ERROR);
+		raise Error_1(RE_USE_FAIL_FOR_ERROR, value);
 
 		// Note: Caller can put the ERROR! in a block or use some other
 		// such trick if it wants to actually throw an error.
-		// (Better than complicating throw with /error-is-intentional!)
+		// (Better than complicating via THROW/ERROR-IS-INTENTIONAL!)
 	}
 
 	if (named) {
@@ -846,13 +846,13 @@ enum {
 		return R_OUT;
 
 	case REB_ERROR:
-	#if !defined(NDEBUG)
-		if (LEGACY(OPTIONS_DO_RAISES_ERRORS))
-			raise Error_Is(value);
-	#endif
-		// This path will no longer raise the error you asked for, though it
-		// will still raise *an* error directing you to use FAIL.)
-		raise Error_0(RE_USE_FAIL_FOR_ERROR);
+		// FAIL is the preferred operation for triggering errors, as it has
+		// a natural behavior for blocks passed to construct readable messages
+		// and "FAIL X" more clearly communicates a failure than "DO X"
+		// does.  However DO of an ERROR! would have to raise an error
+		// anyway, so it might as well raise the one it is given.
+		//
+		raise Error_Is(value);
 
 	case REB_TASK:
 		Do_Task(value);

src/mezz/mezz-legacy.r

@@ -216,7 +216,6 @@ set 'r3-legacy* func [] [
 	; at different times on a case-by-case basis.
 	;
 	system/options/do-runs-functions: true
-	system/options/do-raises-errors: true
 	system/options/broken-case-semantics: true
 	system/options/exit-functions-only: true
 	system/options/datatype-word-strict: true