Make bare ampersands a separate error

README.md

@@ -42,13 +42,21 @@ Entities must be of one of the following forms:
 - `&nnnn;`, where *nnnn* is a Unicode code point in base 10
 - `&#xhhhh;`, where *hhhh* is a Unicode code point in base 16
 
-A malformed entity is an ampersand not followed by a sequence of characters that matches one of the above forms. This includes when the semicolon is missing, and bare ampersands (i.e. followed by whitespace or as the last character).
+A malformed entity is an ampersand not followed by a sequence of characters that matches one of the above forms. This includes when the semicolon is missing.
 
 Note that this is different from `HBE_PARSE_INVALID_ENTITY`, which is when a well-formed entity references a non-existent entity name or Unicode code point.
 
+While an ampersand by itself (i.e. followed by whitespace or as the last character) is a malformed entity, it is covered by `HBE_PARSE_BARE_AMPERSAND`.
+
+#### `HBE_PARSE_BARE_AMPERSAND` ⌫
+
+It's an error to have an ampersand followed by whitespace or as the last character.
+
+This is intentionally a different error to `HBE_PARSE_MALFORMED_ENTITY` due to the ubiquity of bare ampersands.
+
 An ampersand by itself is not *necessarily* an invalid entity. However, HTML parsers and browsers may have different interpretations of bare ampersands, so it's a good idea to always use the encoded form (`&`).
 
-When this error is suppressed, malformed entities are outputted untouched.
+When this error is suppressed, bare ampersands are outputted untouched.
 
 #### `HBE_PARSE_INVALID_ENTITY` ⌫
 

src/main/c/error/error.c

@@ -36,6 +36,7 @@ typedef enum hbe_errcode {
   HBE_MEM_ALLOC_FAIL,
 
   HBE_PARSE_MALFORMED_ENTITY = 65,
+  HBE_PARSE_BARE_AMPERSAND,
   HBE_PARSE_INVALID_ENTITY,
   HBE_PARSE_NONSTANDARD_TAG,
   HBE_PARSE_UCASE_TAG,

src/main/c/main.c

@@ -92,6 +92,8 @@ static void _parse_and_add_errors_to_suppress(nh_set_int32_t suppressed_errors,
 
     if (hbu_buffer_compare_lit(part, "MALFORMED_ENTITY") == 0) {
       nh_set_int32_add(suppressed_errors, HBE_PARSE_MALFORMED_ENTITY);
+    } else if (hbu_buffer_compare_lit(part, "BARE_AMPERSAND") == 0) {
+      nh_set_int32_add(suppressed_errors, HBE_PARSE_BARE_AMPERSAND);
     } else if (hbu_buffer_compare_lit(part, "INVALID_ENTITY") == 0) {
       nh_set_int32_add(suppressed_errors, HBE_PARSE_INVALID_ENTITY);
     } else if (hbu_buffer_compare_lit(part, "NONSTANDARD_TAG") == 0) {

src/main/c/stream/entity.c

@@ -54,6 +54,14 @@ static void _hbs_entity_handle_error(hbs_options_t so, hbu_pipe_t pipe, int type
 void hbs_entity(hbs_options_t so, hbu_pipe_t pipe) {
   hbu_pipe_require_skip(pipe, '&');
 
+  // Quickly check and short circuit if BARE_AMPERSAND is suppressed
+  // and next character is whitespace
+  if (hbs_options_supressed_error(so, HBE_PARSE_BARE_AMPERSAND) &&
+      hbr_whitespace_check(hbu_pipe_peek_eoi(pipe))) {
+    hbu_pipe_write(pipe, '&');
+    return;
+  }
+
   hb_char_t c = hbu_pipe_peek(pipe);
 
   // _hbs_entity_handle_error will free this in case of error