parser: Show error instead of warning for byref function without result

This fixes #755. Of course the check is simple and won't catch all possible
cases - it only checks whether the function result was set once, but it
does not check whether it was set on all code paths.

Author: dkl

changelog.txt

@@ -64,6 +64,7 @@ Version 1.01.0
 - When passing a constant zero of some integer to an overloaded procedure, overloads with integer parameters will now be preferred over overloads with pointers (literal 0 can still be passed to pointer parameters in this case though, by casting it to the pointer type)
 - Literal zeroes with [U]Byte or [U]Short type (or the 16bit Integer in -lang qb) can now be passed to pointer parameters of overloaded procedures (now it's possible to call Bsave() with 0 source buffer in -lang qb again -- it also was affected by this bug since FB 0.90)
 - #760: RETURN and FUNCTION= couldn't be used together in byref functions returning an UDT with constructor. This check is now only applied to functions returning byval.
+- #755: If no result is set in byref functions, the compiler will now show an error instead of a warning (because a byref function defaults to returning a null reference, most likely causing a crash at runtime)
 
 
 Version 1.00.0 (former 0.91.0):

src/compiler/error.bas

@@ -395,7 +395,8 @@ declare function hMakeParamDesc _
 		@"vararg parameters are only allowed in CDECL procedures", _
 		@"the first parameter in a procedure may not be vararg", _
 		@"CONST used on constructor (not needed)", _
-		@"CONST used on destructor (not needed)" _
+		@"CONST used on destructor (not needed)", _
+		@"Byref function result not set" _
 	}
 
 

src/compiler/error.bi

@@ -317,6 +317,7 @@ enum FB_ERRMSG
 	FB_ERRMSG_VARARGNOTALLOWEDASFIRSTPARAM
 	FB_ERRMSG_CONSTCTOR
 	FB_ERRMSG_CONSTDTOR
+	FB_ERRMSG_NOBYREFFUNCTIONRESULT
 
 	FB_ERRMSGS
 end enum

src/compiler/parser-proc.bas

@@ -1818,7 +1818,11 @@ sub cProcStmtEnd( )
 	if( proc_res <> NULL ) then
 		if( symbGetIsAccessed( proc_res ) = FALSE ) then
 			if( symbIsNaked( parser.currproc ) = FALSE ) then
-				errReportWarn( FB_WARNINGMSG_NOFUNCTIONRESULT )
+				if( symbProcReturnsByref( parser.currproc ) ) then
+					errReport( FB_ERRMSG_NOBYREFFUNCTIONRESULT )
+				else
+					errReportWarn( FB_WARNINGMSG_NOFUNCTIONRESULT )
+				end if
 			end if
 		end if
 	end if

tests/functions/return-byref-no-result-assignment.bas

@@ -0,0 +1,4 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+function f( ) byref as integer
+end function