compiler: -Wundefined now also works for old-style patches

Old style assumes everything is implicitly initialized to zero.
We can still report identifiers that are never assigned to, though.

New style allows explicit initialization and thus can report
uninitialized variables immediately when they're read.

src/compiler/parser.y

@@ -228,6 +228,14 @@ start ::= TOK_START_EXPR expr(N). {
 }
 
 start ::= TOK_START_ASSIGN sections. {
+	if(warn_undefined && state->style == old_style) {
+		const struct sym *sym;
+
+		forall_syms(sym)
+			if(!(sym->flags & (SF_SYSTEM | SF_ASSIGNED)))
+				printf("variable %s is only read, never set\n",
+				    sym->fpvm_sym.name);
+	}
 	state->success = 1;
 }
 
@@ -274,6 +282,7 @@ assignment ::= ident(I) TOK_ASSIGN expr(N) opt_semi. {
 			FAIL;
 			return;
 		}
+		IS_STYLE(new_style);
 	} else {
 		state->error =
 		    state->comm->assign_default(state->comm, I->sym, N);
@@ -499,7 +508,8 @@ primary_expr(N) ::= TOK_CONSTANT(C). {
 }
 
 primary_expr(N) ::= ident(I). {
-	if(warn_undefined && !(I->sym->flags & (SF_SYSTEM | SF_ASSIGNED)))
+	if(warn_undefined && state->style == new_style &&
+	    !(I->sym->flags & (SF_SYSTEM | SF_ASSIGNED)))
 		printf("accessing undefined variable %s\n",
 		    I->sym->fpvm_sym.name);
 	N = node(I->token, I->sym, NULL, NULL, NULL);

src/compiler/test/wundef

@@ -55,4 +55,23 @@ expect <<EOF
 accessing undefined variable foo
 EOF
 
+#------------------------------------------------------------------------------
+
+ptest "-Wundefined: old-style read-modify-write" -q -Wundefined <<EOF
+per_vertex =
+	foo = foo
+EOF
+expect <<EOF
+EOF
+
+#------------------------------------------------------------------------------
+
+ptest "-Wundefined: old-style undefined" -q -Wundefined <<EOF
+per_vertex =
+	foo = bar
+EOF
+expect <<EOF
+variable bar is only read, never set
+EOF
+
 ###############################################################################