Minify class attribute values

README.md

@@ -276,6 +276,8 @@ Tags not in one of the categories below are **specific tags**.
 
 ### Options
 
+Note that only existing whitespace will be up for removal via minification. Entities that represent whitespace will not be decoded and then removed.
+
 For options that have a list of tags as their values, the tags should be separated by a comma.
 
 An `*` (asterisk, U+002A) can be used to represent the complete set of possible tags. It essentially fully enables or disables the option.
@@ -429,7 +431,7 @@ The following removal of attributes and tags as minification strategies are not
 
 If they exist, it is assumed there is a special reason for being so.
 
-- Remove empty attributes
+- Remove empty attributes (including ones that would be empty after minification e.g. `class="   "`)
 - Remove empty elements
 - Remove redundant attributes
 - Remove `type` attribute on `<script>` tags

src/main/c/stream/helper/attr.c

@@ -36,12 +36,15 @@ void hbsh_attr(hbs_options_t so, hbu_pipe_t pipe) {
     }
   }
 
+  int collapse_and_trim_whitespace = hbu_buffer_compare_lit(name, "class") == 0 &&
+                                     so->trim_class_attr;
+
   hbu_buffer_destroy(name);
 
   if (hbu_pipe_accept_if(pipe, '=')) {
     if (hbr_attrvalquote_check(hbu_pipe_peek(pipe))) {
       // Quoted attribute value
-      hbsh_quoteattrval(pipe);
+      hbsh_quoteattrval(pipe, collapse_and_trim_whitespace);
     } else {
       if (!hbs_options_supressed_error(so, HBE_PARSE_UNQUOTED_ATTR)) {
         hbu_pipe_error(pipe, HBE_PARSE_UNQUOTED_ATTR, "Unquoted attribute value");

src/main/c/stream/helper/quoteattrval.c

@@ -6,11 +6,26 @@
 #include "../../util/hbchar.h"
 #include "../../util/pipe.c"
 
-void hbsh_quoteattrval(hbu_pipe_t pipe) {
+void hbsh_quoteattrval(hbu_pipe_t pipe, int collapse_and_trim_whitespace) {
   hb_char_t quote_char = hbu_pipe_require_predicate(pipe, &hbr_attrvalquote_check, "attribute value quote");
 
-  while (hbu_pipe_peek(pipe) != quote_char) {
-    hbu_pipe_accept(pipe);
+  int whitespace = 0;
+  if (collapse_and_trim_whitespace) {
+    hbu_pipe_skip_while_predicate(pipe, &hbr_whitespace_check);
+  }
+
+  hb_char_t c;
+
+  while ((c = hbu_pipe_peek(pipe)) != quote_char) {
+    if (collapse_and_trim_whitespace && hbr_whitespace_check(c)) {
+      whitespace = 1;
+      hbu_pipe_skip(pipe);
+    } else {
+      if (whitespace) {
+        hbu_pipe_write(pipe, ' ');
+      }
+      hbu_pipe_accept(pipe);
+    }
   }
 
   hbu_pipe_require(pipe, quote_char);