kbuild: Warn on selecting symbols with unmet direct dependencies

The "select" statement in Kconfig files allows the enabling of options
even if they have unmet direct dependencies (i.e. "depends on" expands
to "no"). Currently, the "depends on" clauses are used in calculating
the visibility but they do not affect the reverse dependencies in any
way.

The patch introduces additional tracking of the "depends on" statements
and prints a warning on selecting an option if its direct dependencies
are not met.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/expr.h

@@ -83,6 +83,7 @@ struct symbol {
 	tristate visible;
 	int flags;
 	struct property *prop;
+	struct expr_value dir_dep;
 	struct expr_value rev_dep;
 };
 
@@ -163,6 +164,7 @@ struct menu {
 	struct symbol *sym;
 	struct property *prompt;
 	struct expr *dep;
+	struct expr *dir_dep;
 	unsigned int flags;
 	char *help;
 	struct file *file;

scripts/kconfig/menu.c

@@ -105,6 +105,7 @@ static struct expr *menu_check_dep(struct expr *e)
 void menu_add_dep(struct expr *dep)
 {
 	current_entry->dep = expr_alloc_and(current_entry->dep, menu_check_dep(dep));
+	current_entry->dir_dep = current_entry->dep;
 }
 
 void menu_set_type(int type)
@@ -288,6 +289,10 @@ void menu_finalize(struct menu *parent)
 		for (menu = parent->list; menu; menu = menu->next)
 			menu_finalize(menu);
 	} else if (sym) {
+		/* ignore inherited dependencies for dir_dep */
+		sym->dir_dep.expr = expr_transform(expr_copy(parent->dir_dep));
+		sym->dir_dep.expr = expr_eliminate_dups(sym->dir_dep.expr);
+
 		basedep = parent->prompt ? parent->prompt->visible.expr : NULL;
 		basedep = expr_trans_compare(basedep, E_UNEQUAL, &symbol_no);
 		basedep = expr_eliminate_dups(expr_transform(basedep));

scripts/kconfig/symbol.c

@@ -205,6 +205,16 @@ static void sym_calc_visibility(struct symbol *sym)
 	}
 	if (sym_is_choice_value(sym))
 		return;
+	/* defaulting to "yes" if no explicit "depends on" are given */
+	tri = yes;
+	if (sym->dir_dep.expr)
+		tri = expr_calc_value(sym->dir_dep.expr);
+	if (tri == mod)
+		tri = yes;
+	if (sym->dir_dep.tri != tri) {
+		sym->dir_dep.tri = tri;
+		sym_set_changed(sym);
+	}
 	tri = no;
 	if (sym->rev_dep.expr)
 		tri = expr_calc_value(sym->rev_dep.expr);
@@ -321,6 +331,14 @@ void sym_calc_value(struct symbol *sym)
 				}
 			}
 		calc_newval:
+			if (sym->dir_dep.tri == no && sym->rev_dep.tri != no) {
+				fprintf(stderr, "warning: (");
+				expr_fprint(sym->rev_dep.expr, stderr);
+				fprintf(stderr, ") selects %s which has unmet direct dependencies (",
+					sym->name);
+				expr_fprint(sym->dir_dep.expr, stderr);
+				fprintf(stderr, ")\n");
+			}
 			newval.tri = EXPR_OR(newval.tri, sym->rev_dep.tri);
 		}
 		if (newval.tri == mod && sym_get_type(sym) == S_BOOLEAN)