Now detects use before declaration, f.i. in

VAR k: REAL;
REAL : INTEGER;

lang/m2/comp/Version.c

@@ -1 +1 @@
-static char Version[] = "ACK Modula-2 compiler Version 0.24";
+static char Version[] = "ACK Modula-2 compiler Version 0.25";

lang/m2/comp/def.H

@@ -98,9 +98,11 @@ struct def	{		/* list of definitions for a name */
 #define D_ERROR		0x4000	/* a compiler generated definition for an
 				   undefined variable
 				*/
+#define D_INUSE		0x8000	/* identification in this scope (like D_IMPORT)
+				*/
 #define D_VALUE	(D_PROCEDURE|D_VARIABLE|D_FIELD|D_ENUM|D_CONST|D_PROCHEAD)
 #define D_ISTYPE	(D_HIDDEN|D_TYPE|D_FTYPE)
-#define D_IMPORTED	(D_IMPORT)
+#define D_IMPORTED	(D_IMPORT|D_INUSE)
 #define is_type(dfx)	((dfx)->df_kind & D_ISTYPE)
 	unsigned short  df_flags;
 #define D_NOREG		0x01	/* set if it may not reside in a register */

lang/m2/comp/def.c

@@ -96,16 +96,22 @@ define(id, scope, kind)
 	*/
 	register t_def *df;
 
-	df = lookup(id, scope, 1, 0);
+	df = lookup(id, scope, 2, 0);
 	if (	/* Already in this scope */
 		df
 	   ||	/* A closed scope, and id defined in the pervasive scope */
 		( 
 		  scopeclosed(scope)
 		&&
-		  (df = lookup(id, PervasiveScope, 1, 0)))
+		  (df = lookup(id, PervasiveScope, 2, 0)))
 	   ) {
 		switch(df->df_kind) {
+		case D_INUSE:
+			if (kind != D_INUSE) {
+				error("identifier \"%s\" already used; may not be redefined in this scope", df->df_idf->id_text);
+			}
+			return df;
+
 		case D_HIDDEN:
 			/* An opaque type. We may now have found the
 			   definition of this type.

lang/m2/comp/lookup.c

@@ -23,6 +23,8 @@
 #include	"type.h"
 #include	"misc.h"
 
+extern int	pass_1;
+
 t_def *
 lookup(id, scope, import, flags)
 	register t_idf *id;
@@ -55,6 +57,7 @@ lookup(id, scope, import, flags)
 		df->df_flags |= flags;
 		if (import) {
 			while (df->df_kind & D_IMPORTED) {
+				if (df->df_kind == D_INUSE && import != 1) break;
 				assert(df->imp_def != 0);
 				df = df->imp_def;
 			}
@@ -66,23 +69,31 @@ lookup(id, scope, import, flags)
 t_def *
 lookfor(id, vis, message, flags)
 	register t_node *id;
-	t_scopelist *vis;
+	register t_scopelist *vis;
 {
 	/*	Look for an identifier in the visibility range started by "vis".
 		If it is not defined create a dummy definition and,
 		if message is set, give an error message
 	*/
-	register t_def *df;
 	register t_scopelist *sc = vis;
+	t_def *df;
 
 	while (sc) {
 		df = lookup(id->nd_IDF, sc->sc_scope, 1, flags);
-		if (df) return df;
+		if (df) {
+			if (pass_1 &&
+			    message && 
+			    sc->sc_scope->sc_level < vis->sc_scope->sc_level &&
+			    ! scopeclosed(vis->sc_scope)) {
+				define(id->nd_IDF, vis->sc_scope, D_INUSE)->
+					imp_def = df;
+			}
+			return df;
+		}
 		sc = nextvisible(sc);
 	}
 
 	if (message) id_not_declared(id);
 
-	df = MkDef(id->nd_IDF, vis->sc_scope, D_ERROR);
+	return MkDef(id->nd_IDF, vis->sc_scope, D_ERROR);
-	return df;
 }

lang/m2/comp/scope.C

@@ -188,7 +188,7 @@ Reverse(pdf)
 		from this list.
 	*/
 	register t_def *df, *df1;
-#define INTERESTING D_MODULE|D_PROCEDURE|D_PROCHEAD|D_VARIABLE
+#define INTERESTING (D_MODULE|D_PROCEDURE|D_PROCHEAD|D_VARIABLE|D_IMPORTED)
 
 	df = 0;
 	df1 = *pdf;

lang/m2/comp/walk.c

@@ -860,8 +860,8 @@ UseWarnings(df)
 			register t_def *df1 = df->imp_def;
 
 			df1->df_flags |= df->df_flags & (D_USED|D_DEFINED);
-			if (df->df_kind == D_IMPORT &&
+			if (df->df_kind == D_INUSE) return;
-			    !(df->df_flags & D_IMP_BY_EXP)) {
+			if ( !(df->df_flags & D_IMP_BY_EXP)) {
 				if (! (df->df_flags & (D_USED | D_DEFINED))) {
 					node_warning(
 						df->df_scope->sc_end,