src: introduce simple hints on incorrect identifier

 # cat test.nft
 define test = "1.2.3.4"

 table ip x {
        chain y {
                ip saddr $text
        }
 }
 # nft -f test.nft
 test.nft:5:13-16: Error: unknown identifier 'text'; did you mean identifier ‘test’?
                 ip saddr $text
                           ^^^^

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 30 insertions, 2 deletions

diff --git a/include/rule.h b/include/rule.h
index 88fed62e..dc5e5b87 100644
--- a/include/rule.h
+++ b/include/rule.h
@@ -112,6 +112,8 @@ extern void symbol_bind(struct scope *scope, const char *identifier,
 extern int symbol_unbind(const struct scope *scope, const char *identifier);
 extern struct symbol *symbol_lookup(const struct scope *scope,
 				    const char *identifier);
+struct symbol *symbol_lookup_fuzzy(const struct scope *scope,
+				   const char *identifier);
 struct symbol *symbol_get(const struct scope *scope, const char *identifier);
 
 enum table_flags {
diff --git a/src/parser_bison.y b/src/parser_bison.y
index dfe30683..e73e1ecd 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -3078,8 +3078,16 @@ variable_expr		:	'$'	identifier
 
 				sym = symbol_get(scope, $2);
 				if (!sym) {
-					erec_queue(error(&@2, "unknown identifier '%s'", $2),
-						   state->msgs);
+					sym = symbol_lookup_fuzzy(scope, $2);
+					if (sym) {
+						erec_queue(error(&@2, "unknown identifier '%s'; "
+								      "did you mean identifier ‘%s’?",
+								      $2, sym->identifier),
+							   state->msgs);
+					} else {
+						erec_queue(error(&@2, "unknown identifier '%s'", $2),
+							   state->msgs);
+					}
 					xfree($2);
 					YYERROR;
 				}
diff --git a/src/rule.c b/src/rule.c
index 0a3c1970..ad300129 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -692,6 +692,24 @@ struct symbol *symbol_lookup(const struct scope *scope, const char *identifier)
 	return NULL;
 }
 
+struct symbol *symbol_lookup_fuzzy(const struct scope *scope,
+				   const char *identifier)
+{
+	struct string_misspell_state st;
+	struct symbol *sym;
+
+	string_misspell_init(&st);
+
+	while (scope != NULL) {
+		list_for_each_entry(sym, &scope->symbols, list)
+			string_misspell_update(sym->identifier, identifier,
+					       sym, &st);
+
+		scope = scope->parent;
+	}
+	return st.obj;
+}
+
 static const char * const chain_type_str_array[] = {
 	"filter",
 	"nat",