parser: Disallow fixed-length strings as BYREF vars/params/results

fixes part of #650

References or pointers to fixed-length strings are not possible in FB
because we have no way to encode the string length in the pointer dtype.
We can only store fixed-length string length on symbols, not on
expressions, which would be needed when dereferencing such a pointer.
Also, currently, taking the address of a fixed-length string produces an
"unbounded" Zstring Ptr.

Previously the string length was just ignored on BYREF symbols, so it seems
best to disallow it to avoid confusion, especially since it doesn't look
like it will be implemented properly soon (though of course that could
still be done).

changelog.txt

@@ -11,6 +11,7 @@ Version 1.05.0
 - FileAttr() was still broken for 64bit - the result value was truncated to 32bit
 - 1.04.0 regression: Under -gen gcc -asm att, support for gcc-style inline asm was broken
 - ld was warning about unsupported linker options on OS X
+- BYREF fixed-length strings (e.g. BYREF myParameter AS ZSTRING * 10) now trigger a compiler error since they are unsupported
 
 
 Version 1.04.0

src/compiler/error.bas

@@ -407,7 +407,8 @@ declare function hMakeParamDesc _
 		@"Reference not initialized", _
 		@"Incompatible reference initializer", _
 		@"Array of references - not supported yet", _
-		@"Invalid CASE range, start value is greater than the end value" _
+		@"Invalid CASE range, start value is greater than the end value", _
+		@"Fixed-length string combined with BYREF (not supported)" _
 	}
 
 

src/compiler/error.bi

@@ -326,6 +326,7 @@ enum FB_ERRMSG
 	FB_ERRMSG_INCOMPATIBLEREFINIT
 	FB_ERRMSG_ARRAYOFREFS
 	FB_ERRMSG_INVALIDCASERANGE
+	FB_ERRMSG_BYREFFIXSTR
 
 	FB_ERRMSGS
 end enum

src/compiler/parser-decl-proc-params.bas

@@ -393,6 +393,7 @@ private function hParamDecl _
 				options or= FB_SYMBTYPEOPT_ALLOWFORWARD
 			end if
 			options and= not FB_SYMBTYPEOPT_CHECKSTRPTR
+			options or= FB_SYMBTYPEOPT_ISBYREF
 		end if
 
 		if( cSymbolType( dtype, subtype, 0, options ) = FALSE ) then

src/compiler/parser-decl-symbtype.bas

@@ -613,6 +613,12 @@ function cSymbolType _
 
 		end select
 
+		'' STRING * N can't be allowed with BYREF or pointers, because
+		'' we can't represent the * N on expression data types.
+		if( options and FB_SYMBTYPEOPT_ISBYREF ) then
+			errReport( FB_ERRMSG_BYREFFIXSTR, TRUE )
+		end if
+
 		'' const?
 		if( is_const ) then
 			dtype = typeSetIsConst( dtype )

src/compiler/parser-decl-var.bas

@@ -44,6 +44,7 @@ sub hSymbolType _
 	dim as integer options = FB_SYMBTYPEOPT_DEFAULT
 	if( is_byref ) then
 		options and= not FB_SYMBTYPEOPT_CHECKSTRPTR
+		options or= FB_SYMBTYPEOPT_ISBYREF
 	end if
 
 	'' parse the symbol type (INTEGER, STRING, etc...)

src/compiler/parser-proc.bas

@@ -396,6 +396,7 @@ sub cProcRetType _
 
 		'' Then allow BYREF AS Z/WSTRING as the type
 		options and= not FB_SYMBTYPEOPT_CHECKSTRPTR
+		options or= FB_SYMBTYPEOPT_ISBYREF
 	end if
 
 	if( cSymbolType( dtype, subtype, 0, options ) = FALSE ) then

src/compiler/parser.bi

@@ -196,6 +196,7 @@ enum FB_SYMBTYPEOPT
 
 	FB_SYMBTYPEOPT_CHECKSTRPTR	= &h00000001
 	FB_SYMBTYPEOPT_ALLOWFORWARD	= &h00000002
+	FB_SYMBTYPEOPT_ISBYREF		= &h00000004
 
 	FB_SYMBTYPEOPT_DEFAULT		= FB_SYMBTYPEOPT_CHECKSTRPTR
 end enum

tests/string/byref-fixlen-1.bas

@@ -0,0 +1,3 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+declare sub f(byref z as zstring * 10)

tests/string/byref-fixlen-2.bas

@@ -0,0 +1,3 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+dim byref z as zstring * 10 = "hi"

tests/string/byref-fixlen-3.bas

@@ -0,0 +1,5 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+function f() byref as zstring * 10
+	return "hi"
+end function

tests/string/byval-fixlen-1.bas

@@ -0,0 +1,3 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+declare sub f(byval z as zstring * 10)

tests/string/byval-fixlen-2.bas

@@ -0,0 +1,5 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+function f() as zstring * 10
+	return "hi"
+end function

todo.txt

@@ -21,7 +21,6 @@ o Dim Byref
        which we don't need. The temp vars from the reference var initializer are in the same
        scope as the reference var, and it should be enough to just remove their TEMP flag.
   - allow BYVAL initialization, like byref results/params
-  - disallow [Z/W]String * N with Dim Byref (same problem as with byref params, see bug #650)
   - allow BYREF fields; but they must be initialized in a constructor - what syntax to use for that?
     @a = b works, but feels like a hack. Otherwise, a new syntax for field initialization is needed,
     like initializer lists in C++