fixes #403

docs/resources/changelog.md

@@ -15,6 +15,7 @@ _During the beta period, these restrictions may be relaxed in the event of a mis
 - Fixed a bug in `sl-tooltip` where they wouldn't display after toggling `disabled` off and on again [#391](https://github.com/shoelace-style/shoelace/issues/391)
 - Fixed a bug in `sl-details` where `show()` and `hide()` would toggle the control when disabled
 - Fixed a bug in `sl-color-picker` where setting `value` wouldn't update the control
+- Fixed a bug in `sl-tab-group` where tabs that are initially disabled wouldn't receive the indicator on activation [#403](https://github.com/shoelace-style/shoelace/issues/403)
 - Fixed incorrect event names for `sl-after-show` and `sl-after-hide` in `sl-details`
 - Improved a11y for disabled buttons that are rendered as links
 - Improved a11y for `sl-button-group` by adding the correct `role` attribute

src/components/tab-group/tab-group.ts

@@ -82,15 +82,18 @@ export default class SlTabGroup extends LitElement {
     this.resizeObserver.observe(this.nav);
     requestAnimationFrame(() => this.updateScrollControls());
 
-    // Update aria labels if the DOM changes
     this.mutationObserver = new MutationObserver(mutations => {
+      // Update aria labels when the DOM changes
       if (
-        mutations.some(mutation => {
-          return !['aria-labelledby', 'aria-controls'].includes(mutation.attributeName as string);
-        })
+        mutations.some(mutation => !['aria-labelledby', 'aria-controls'].includes(mutation.attributeName as string))
       ) {
         setTimeout(() => this.setAriaLabels());
       }
+
+      // Sync tabs when disabled states change
+      if (mutations.some(mutation => mutation.attributeName === 'disabled')) {
+        this.syncTabsAndPanels();
+      }
     });
     this.mutationObserver.observe(this, { attributes: true, childList: true, subtree: true });
   }
@@ -312,6 +315,7 @@ export default class SlTabGroup extends LitElement {
     });
   }
 
+  // This stores tabs and panels so we can refer to a cache instead of calling querySelectorAll() multiple times.
   syncTabsAndPanels() {
     this.tabs = this.getAllTabs();
     this.panels = this.getAllPanels();