Link "skip empty diffs" with "without formatting"

When users are comparing diffs without formatting they expect "skip
empty diffs" to skip pages that only differ by formatting. This links
the two together so that it behaves the way that expect.

tools/project_manager/diff.php

@@ -171,6 +171,42 @@ function copyToClip(textstring) {
     echo $navigation_text;
 }
 
+// Load an associative array for which pages in the project have diffs.
+function load_page_diff_array(Project $project, $L_round, $R_round, bool $include_no_format = false): array
+{
+    if ($include_no_format) {
+        $un_formatter = new PageUnformatter();
+        $text_columns = "
+            $L_round->text_column_name as L_text,
+            $R_round->text_column_name as R_text,
+        ";
+    } else {
+        $text_columns = "";
+    }
+    $sql = "
+        SELECT image,
+            $L_round->user_column_name as username,
+            $text_columns
+            CAST($L_round->text_column_name AS BINARY) = CAST($R_round->text_column_name AS BINARY) AS is_same
+        FROM $project->projectid
+        ORDER BY image ASC
+    ";
+    $res = DPDatabase::query($sql);
+    $result = [];
+    while ($row = mysqli_fetch_assoc($res)) {
+        $result[$row["image"]] = [
+            "username" => $row["username"],
+            "is_diff" => ! $row["is_same"],
+        ];
+        if ($include_no_format) {
+            $L_text = $un_formatter->remove_formatting($row["L_text"], false);
+            $R_text = $un_formatter->remove_formatting($row["R_text"], false);
+            $result[$row["image"]]["is_diff_without_formatting"] = $L_text != $R_text;
+        }
+    }
+    return $result;
+}
+
 /**
  * Build up the text for the navigation bit, so we can repeat it
  * again at the bottom of the page
@@ -199,27 +235,24 @@ function get_navigation(
     }
     $navigation_text .= "\n" . _("Jump to") . ": <select name='jumpto' onChange='$jump_to_js'>\n";
 
-    $query = "
-        SELECT image,
-            $L_round->user_column_name,
-            CAST($L_round->text_column_name AS BINARY) = CAST($R_round->text_column_name AS BINARY) AS is_empty_diff
-        FROM $project->projectid
-        ORDER BY image ASC
-    ";
-    $res = DPDatabase::query($query);
+    $diff_array = load_page_diff_array($project, $L_round, $R_round, $format == "remove");
+
     $prev_image = "";
     $next_image = "";
     $prev_from_proofer = "";
     $next_from_proofer = "";
     $got_there = false;
     // construct the dropdown; work out where previous and next buttons should take us
-    while ([$this_val, $this_user, $is_empty_diff] = mysqli_fetch_row($res)) {
+    foreach ($diff_array as $this_val => $diff_record) {
+        $this_user = $diff_record["username"];
+        $is_diff = $format == "remove" ? $diff_record["is_diff_without_formatting"] : $diff_record["is_diff"];
+
         $navigation_text .= "\n<option value='$this_val'";
 
         if ($this_val == $image) {
             $navigation_text .= " selected";  // make the correct element of the drop down selected
             $got_there = true;
-        } elseif ($only_nonempty_diffs && $is_empty_diff) {
+        } elseif ($only_nonempty_diffs && !$is_diff) {
             $navigation_text .= " disabled"; // Disable empty diffs in the dropdown and skip the other checks
         } elseif ($got_there) {
             // we are at the one after the current one
@@ -270,9 +303,9 @@ function get_navigation(
     }
 
     $checked_attribute = $only_nonempty_diffs ? 'checked' : '';
-
+    $checkbox_title = $format == "remove" ? _('Skip empty diffs, ignoring formatting') : _('Skip empty diffs');
     $navigation_text .= "\n<input type='checkbox' name='only_nonempty_diffs' $checked_attribute id='only_nonempty_diffs' onclick='this.form.submit()'>\n";
-    $navigation_text .= "\n<label for='only_nonempty_diffs'>" . html_safe(_('Skip empty diffs')) . "</label>\n";
+    $navigation_text .= "\n<label for='only_nonempty_diffs'>" . html_safe($checkbox_title) . "</label>\n";
     $navigation_text .= "\n</form>\n";
 
     return $navigation_text;