Fix case-sensitivity issue with rendering suggested tags.

The `TagEditor` component formerly did not take casing into account
in its formatting function for suggested tags. The match should be
case-insensitive in the formatter, as it is in the service that does
the filtering of tags.

This is fixed in two ways:

1. Make substring matching in the formatting function case-insensitive.
   Render the substring match according to the suggested tag's casing.
   Fixes this issue specifically.
2. Provide a fallback in the formatter for when the input text does not
   "seem" to match the suggested `item`. In these cases, just render the
   suggested tag as-is. This will prevent the formatter from spazzing
   out if its notion of matching differs from the tag-service's in
   any future case.

Fixes #2547

src/sidebar/components/tag-editor.js

@@ -244,15 +244,32 @@ function TagEditor({
    * @param {string} item - Suggested tag
    * @return {JSXElement} - Formatted tag for use in list
    */
-  const formatSuggestItem = item => {
-    const curVal = pendingTag();
-    const prefix = item.slice(0, item.indexOf(curVal));
-    const suffix = item.slice(item.indexOf(curVal) + curVal.length);
+  const formatSuggestedItem = item => {
+    // filtering of tags is case-insensitive
+    const curVal = pendingTag().toLowerCase();
+    const suggestedTag = item.toLowerCase();
+    const matchIndex = suggestedTag.indexOf(curVal);
+
+    // If the current input doesn't seem to match the suggested tag,
+    // just render the tag as-is.
+    if (matchIndex === -1) {
+      return <span>{item}</span>;
+    }
+
+    // Break the suggested tag into three parts:
+    // 1. Substring of the suggested tag that occurs before the match
+    //    with the current input
+    const prefix = item.slice(0, matchIndex);
+    // 2. Substring of the suggested tag that matches the input text. NB:
+    //    This may be in a different case than the input text.
+    const matchString = item.slice(matchIndex, matchIndex + curVal.length);
+    // 3. Substring of the suggested tag that occurs after the matched input
+    const suffix = item.slice(matchIndex + curVal.length);
 
     return (
       <span>
         <strong>{prefix}</strong>
-        {curVal}
+        {matchString}
         <strong>{suffix}</strong>
       </span>
     );
@@ -324,7 +341,7 @@ function TagEditor({
         <AutocompleteList
           id={`${tagEditorId}-autocomplete-list`}
           list={suggestions}
-          listFormatter={formatSuggestItem}
+          listFormatter={formatSuggestedItem}
           open={suggestionsListOpen}
           onSelectItem={handleSelect}
           itemPrefixId={`${tagEditorId}-autocomplete-list-item-`}

src/sidebar/components/test/tag-editor-test.js

@@ -116,6 +116,56 @@ describe('TagEditor', function () {
     assert.equal(wrapper.find('AutocompleteList').prop('list')[1], 'tag4');
   });
 
+  it('shows case-insensitive matches to suggested tags', () => {
+    fakeTagsService.filter.returns(['fine AArdvark', 'AAArgh']);
+    const wrapper = createComponent();
+    wrapper.find('input').instance().value = 'aa';
+    typeInput(wrapper);
+
+    const formattingFn = wrapper.find('AutocompleteList').prop('listFormatter');
+    const tagList = wrapper.find('AutocompleteList').prop('list');
+
+    const firstSuggestedTag = mount(formattingFn(tagList[0]))
+      .find('span')
+      .text();
+    const secondSuggestedTag = mount(formattingFn(tagList[1]))
+      .find('span')
+      .text();
+
+    // Even though the entered text was lower case ('aa'), the suggested tag
+    // should be rendered with its original casing (upper-case here)
+    assert.equal(firstSuggestedTag, 'AAArgh');
+    assert.equal(secondSuggestedTag, 'fine AArdvark');
+  });
+
+  it('shows suggested tags as-is if they do not seem to match the input', () => {
+    // This case addresses a situation in which a substring match isn't found
+    // for the current input text against a given suggested tag. This should not
+    // happen in practice—i.e. filtered tags should match the current input—
+    // but there is no contract that the tags service filtering uses the same
+    // "matching" as the component, so we should be able to handle cases where
+    // there doesn't "seem" to be a match by just rendering the suggested tag
+    // as-is.
+    fakeTagsService.filter.returns(['fine AArdvark', 'AAArgh']);
+    const wrapper = createComponent();
+    wrapper.find('input').instance().value = 'bb';
+    typeInput(wrapper);
+
+    const formattingFn = wrapper.find('AutocompleteList').prop('listFormatter');
+    const tagList = wrapper.find('AutocompleteList').prop('list');
+
+    const firstSuggestedTag = mount(formattingFn(tagList[0]))
+      .find('span')
+      .text();
+    const secondSuggestedTag = mount(formattingFn(tagList[1]))
+      .find('span')
+      .text();
+
+    // Obviously, these don't have a `bb` substring; we'll just render them...
+    assert.equal(firstSuggestedTag, 'AAArgh');
+    assert.equal(secondSuggestedTag, 'fine AArdvark');
+  });
+
   it('passes the text value to filter() after receiving input', () => {
     const wrapper = createComponent();
     wrapper.find('input').instance().value = 'tag3';