builtin/cd: fix SEGFAULT when HOME or PWD has not been set

This can be reproduced using:

  $ env -i ./minishell
  cd -

and

  $ env -i ./minishell
  cd

and

  $ env -i ./minishell
  cd ~

inc/env.h

@@ -28,5 +28,6 @@ int					env_unset(struct s_env **env, char *key);
 char				**env_to_envp(struct s_env *env);
 void				env_free(struct s_env **env);
 int					env_is_valid_key(char *key);
+int					env_has(struct s_env *env, char *key);
 
 #endif

src/builtin/cd.c

@@ -21,39 +21,39 @@
 #include "env.h"
 #include "builtin.h"
 
-static void	cd(t_env **env, char *cwd)
+static int	cd(t_env **env, char *old_path, char *new_path)
 {
-	char	*old_pwd;
-
-	old_pwd = env_get(*env, "PWD");
-	env_set(env, "OLDPWD", old_pwd);
-	env_set(env, "PWD", cwd);
-	ft_strdel(&old_pwd);
+	if (chdir(new_path) == -1)
+		return (-1);
+	env_set(env, "OLDPWD", old_path);
+	env_set(env, "PWD", new_path);
+	return (0);
 }
 
 int			builtin_cd(int argc, char **argv, t_env **env)
 {
-	char	to_path[PATH_MAX];
-	char	cwd[PATH_MAX];
+	char	old_path[PATH_MAX];
+	char	new_path[PATH_MAX];
 
-	getcwd(cwd, PATH_MAX);
+	getcwd(old_path, PATH_MAX);
 	if (argc > 2)
 		return (ft_eprintf(1, "cd: to many arguments\n"));
 	if (argc == 1)
-		ft_strlcpy(to_path, env_get_unsafe_ptr(*env, "HOME"), PATH_MAX);
-	else if (ft_strncmp(argv[1], "~", 1) == 0)
-		ft_snprintf(to_path, PATH_MAX, "%s%s",
-			env_get_unsafe_ptr(*env, "HOME"), argv[1] + 1);
+	{
+		if (!env_has(*env, "HOME"))
+			return (ft_eprintf(1, "cd: $HOME not set\n"));
+		ft_strlcpy(new_path, env_get_unsafe_ptr(*env, "HOME"), PATH_MAX);
+	}
 	else if (ft_strcmp(argv[1], "-") == 0)
 	{
-		ft_strlcpy(to_path, env_get_unsafe_ptr(*env, "OLDPWD"), PATH_MAX);
-		ft_printf("%s\n", to_path);
+		if (!env_has(*env, "OLDPWD"))
+			return (ft_eprintf(1, "cd: $OLDPWD not set\n"));
+		ft_strlcpy(new_path, env_get_unsafe_ptr(*env, "OLDPWD"), PATH_MAX);
+		ft_printf("%s\n", new_path);
 	}
 	else
-		ft_strlcpy(to_path, argv[1], PATH_MAX);
-	if (chdir(to_path) == 0)
-		cd(env, cwd);
-	else
-		return (ft_eprintf(1, "cd: unable to change dir '%s'\n", to_path));
+		ft_strlcpy(new_path, argv[1], PATH_MAX);
+	if (cd(env, old_path, new_path) == -1)
+		return (ft_eprintf(1, "cd: unable to change dir '%s'\n", new_path));
 	return (0);
 }

src/env/keyvalue.c

@@ -69,3 +69,8 @@ int			env_unset(struct s_env **head, char *key)
 	*head = next;
 	return (0);
 }
+
+int			env_has(struct s_env *env, char *key)
+{
+	return (env_get_unsafe_ptr(env, key) != NULL);
+}

src/expand.c

@@ -75,10 +75,10 @@ static char	*expand_arg(t_env *env, char *arg)
 	size_t	offset;
 	char	*new_line;
 
-	if (ft_strncmp(arg, "~/", 2) == 0)
+	if (env_has(env, "HOME") && ft_strncmp(arg, "~/", 2) == 0)
 		ft_asprintf(&new_line, "%s/%s",
 			env_get_unsafe_ptr(env, "HOME"), arg + 2);
-	else if (ft_strcmp(arg, "~") == 0)
+	else if (env_has(env, "HOME") && ft_strcmp(arg, "~") == 0)
 		new_line = env_get(env, "HOME");
 	else
 		new_line = ft_strdup(arg);