get_next_token returns result which includes possible error and token

src/lexer/lexer.c

@@ -92,6 +92,7 @@ struct lexer {
   token_t token;
   bool has_extra_token;
   token_t extra_token;
+  dstr_t *error_message;
 };
 
 void stack_push(state_stack_t *stack, lexer_state_t value);
@@ -104,7 +105,7 @@ bool is_valid_hex_char(const char input);
 bool ishex(const char input);
 
 token_t dstr_to_numerical_token(const dstr_t *str);
-void set_token(token_t *token, u64 line, u64 column, token_type_t type,
+void set_token(token_t *token, u64 line, u64 column, token_type type,
                token_value_t value);
 
 void lexer_state_machine(lexer_t *lexer, char input);
@@ -153,6 +154,7 @@ void lexer_init(lexer_t **lexer) {
   (*lexer)->keyword.type = LEXER_STRING_KEYWORD;
   (*lexer)->codepoint.type = LEXER_STRING_UNICODE;
   (*lexer)->current_string = dstr_with_capacity(STRING_BUF_START_CAPACITY);
+  (*lexer)->error_message = dstr_with_capacity(STRING_BUF_START_CAPACITY);
   (*lexer)->token_ready = false;
   (*lexer)->token = (token_t){0};
   (*lexer)->has_extra_token = false;
@@ -168,11 +170,14 @@ void lexer_free(lexer_t **lexer) {
     return;
   }
 
+  dstr_free(&((*lexer)->current_string));
+  dstr_free(&((*lexer)->error_message));
+
   free(*lexer);
   *lexer = NULL;
 }
 
-token_t get_next_token(lexer_t *lexer, const char *text) {
+lex_result_t get_next_token(lexer_t *lexer, const char *text) {
   if (text != NULL) {
     lexer->cursor = 0;
     lexer->text = text;
@@ -187,7 +192,10 @@ token_t get_next_token(lexer_t *lexer, const char *text) {
     if (lexer->has_extra_token) {
       lexer->has_extra_token = false;
 
-      return lexer->extra_token;
+      return (lex_result_t){
+          (lex_err_t){.errno = LEX_ERR_NONE, .msg = ""},
+          lexer->extra_token,
+      };
     }
 
     c = lexer->text[(lexer->cursor)++];
@@ -202,14 +210,40 @@ token_t get_next_token(lexer_t *lexer, const char *text) {
     }
 
     if (lexer->current == LEXER_STATE_ERROR) {
+      char msg[STRING_BUF_START_CAPACITY + 1];
+      memset(msg, 0, STRING_BUF_START_CAPACITY + 1);
+
+      u64 slice_length = 20;
+      char slice[slice_length];
+      snprintf(slice, slice_length, "%s", &(lexer->text[lexer->cursor - 1]));
+
+      snprintf(
+          msg, STRING_BUF_START_CAPACITY,
+          "\n(%llu:%llu) Encountered an error while parsing the following:\n%s",
+          (unsigned long long)lexer->line, (unsigned long long)lexer->column,
+          slice);
+
+      dstr_update(&(lexer->error_message), msg);
+
+      return (lex_result_t){
+          (lex_err_t){.errno = LEX_ERR_INVALID,
+                      .msg = dstr_to_cstr(lexer->error_message)},
+          (token_t){0},
+      };
     } else if (lexer->token_ready) {
       lexer->token_ready = false;
 
-      return lexer->token;
+      return (lex_result_t){
+          (lex_err_t){.errno = LEX_ERR_NONE, .msg = ""},
+          lexer->token,
+      };
     }
   }
 
-  return (token_t){0};
+  return (lex_result_t){
+      (lex_err_t){.errno = LEX_ERR_NONE, .msg = ""},
+      (token_t){0},
+  };
 }
 
 bool validate_json(char *json) {
@@ -401,7 +435,7 @@ token_t dstr_to_numerical_token(const dstr_t *str) {
   return token;
 }
 
-void set_token(token_t *token, u64 line, u64 column, token_type_t type,
+void set_token(token_t *token, u64 line, u64 column, token_type type,
                token_value_t value) {
   *token = (token_t){
       .line = line,

src/main.c

@@ -35,11 +35,21 @@ int main(int argc, char *argv[]) {
     return EXIT_FAILURE;
   }
 
-  token_t token = get_next_token(lexer, json);
-  while (token.type != TK_NO_TOKEN) {
-    print_token(token);
+  lex_result_t result = get_next_token(lexer, json);
 
-    token = get_next_token(lexer, NULL);
+  if (result.error.errno) {
+    printf("%s\n", result.error.msg);
+  } else {
+    while (result.token.type != TK_NO_TOKEN) {
+      print_token(result.token);
+
+      result = get_next_token(lexer, NULL);
+
+      if (result.error.errno) {
+        printf("%s\n", result.error.msg);
+        break;
+      }
+    }
   }
 
   lexer_free(&lexer);