fix: heap-use-after-free and memory leaks on erorr cases

src/parser/grammar.c

@@ -238,16 +238,20 @@ struct ast *parse_input(struct lexer_context *ctx)
     }
 
     struct ast *ast = parse_list(ctx);
-    if (ast == NULL)
-        return NULL;
-
     token = PEEK_TOKEN();
-    if (token->type == TOKEN_NEWLINE || token->type == TOKEN_EOF)
+
+    if (ast == NULL)
     {
-        if (token->type == TOKEN_NEWLINE)
+        if (token != NULL && token->type == TOKEN_EOF)
         {
             POP_TOKEN();
         }
+        return NULL;
+    }
+
+    if (token->type == TOKEN_NEWLINE || token->type == TOKEN_EOF)
+    {
+        POP_TOKEN();
         return ast;
     }
 

src/parser/grammar_basic.c

@@ -329,12 +329,13 @@ struct ast *parse_if_rule(struct lexer_context *ctx)
     struct ast *condition_content = parse_compound_list(ctx);
 
     // Then keyword
-    token = POP_TOKEN();
+    token = PEEK_TOKEN();
     if (token->type != TOKEN_THEN)
     {
         perror("Expected the 'then' keyword but token has different type");
         return err_if_rule(&condition_content, NULL, NULL);
     }
+    POP_TOKEN();
 
     // Then content
     struct ast *then_content = parse_compound_list(ctx);
@@ -344,6 +345,7 @@ struct ast *parse_if_rule(struct lexer_context *ctx)
     }
 
     struct ast *else_content = NULL;
+    token = PEEK_TOKEN();
     // Eventual else/elif clause(s)
     if (is_first(*token, RULE_ELSE_CLAUSE))
     {
@@ -355,12 +357,13 @@ struct ast *parse_if_rule(struct lexer_context *ctx)
     }
 
     // Fi keyword
-    token = POP_TOKEN();
+    token = PEEK_TOKEN();
     if (token->type != TOKEN_FI)
     {
         perror("Expected the 'fi' keyword but token has different type");
         return err_if_rule(&condition_content, &then_content, &else_content);
     }
+    POP_TOKEN();
 
     // Result
     struct ast *result =