after 9000 hours it finally works

src/components/settings_modal/settings_modal_user_content.js

@@ -88,6 +88,12 @@ const SettingsModalContent = {
       // Clear the state of target tab, so that next time settings is opened
       // it doesn't force it.
       useInterfaceStore().clearSettingsModalTargetTab()
+    },
+    nestedTooBig () {
+      this.$refs.tabSwitcher.showNav()
+    },
+    nestedTooSmall () {
+      this.$refs.tabSwitcher.hideNav()
     }
   },
   mounted () {

src/components/settings_modal/settings_modal_user_content.vue

@@ -2,24 +2,33 @@
   <vertical-tab-switcher
     ref="tabSwitcher"
     class="settings_tab-switcher"
-    :side-tab-bar="true"
     :scrollable-tabs="true"
     :body-scroll-lock="bodyLock"
   >
     <div
+      :full-width="true"
       :label="$t('settings.general')"
       icon="wrench"
       data-tab-name="general"
     >
-      <GeneralTab />
+      <GeneralTab
+        class="inner-tab -middle"
+        @too-small="() => nestedTooSmall()"
+        @too-big="() => nestedTooBig()"
+      />
     </div>
     <div
+      :full-width="true"
       :label="$t('settings.appearance')"
       icon="window-restore"
       data-tab-name="appearance"
       :delay-render="true"
     >
-      <AppearanceTab />
+      <AppearanceTab
+        class="inner-tab -middle"
+        @too-small="() => nestedTooSmall()"
+        @too-big="() => nestedTooBig()"
+      />
     </div>
     <div
       v-if="expertLevel > 0"

src/components/settings_modal/tabs/appearance_tab.vue

@@ -5,6 +5,8 @@
     ref="tabSwitcher"
     :side-tab-bar="true"
     :scrollable-tabs="true"
+    @too-small="() => console.log('small') || $emit('tooSmall')"
+    @too-big="() => $emit('tooBig')"
   >
     <div
       :label="$t('settings.interface')"

src/components/settings_modal/tabs/general_tab.vue

@@ -3,6 +3,8 @@
     :label="$t('settings.general')"
     ref="tabSwitcher"
     class="settings_tab-switcher"
+    @too-small="() => $emit('tooSmall')"
+    @too-big="() => $emit('tooBig')"
   >
     <div
       :label="$t('settings.behavior')"

src/components/tab_switcher/tab_switcher.jsx

@@ -158,7 +158,10 @@ export default {
     })
 
     return (
-      <div class="tab-switcher top-tabs">
+      <div
+        class="tab-switcher top-tabs"
+        ref="root"
+      >
         <div
           class="tabs"
           role="tablist"
@@ -170,6 +173,7 @@ export default {
           role="tabpanel"
           class={'contents' + (this.scrollableTabs ? ' scrollable-tabs' : '')}
           v-body-scroll-lock={this.bodyScrollLock}
+          ref="content"
         >
           {contents}
         </div>

src/components/tab_switcher/vertical_tab_switcher.jsx

@@ -34,10 +34,12 @@ export default {
       default: false
     }
   },
+  emits: ['tooBig', 'tooSmall'],
   data () {
     return {
       active: findFirstUsable(this.slots()),
-      resizeHandler: null
+      resizeHandler: null,
+      navMode: false
     }
   },
   computed: {
@@ -59,6 +61,16 @@ export default {
       mobileLayout: store => store.layoutType === 'mobile'
     }),
   },
+  created () {
+    this.resizeHandler = throttle(this.onResize, 200)
+    window.addEventListener('resize', this.resizeHandler)
+  },
+  mounted () {
+    this.resizeHandler()
+  },
+  unmounted () {
+    window.removeEventListener('resize', this.resizeHandler)
+  },
   beforeUpdate () {
     const currentSlot = this.slots()[this.active]
     if (!currentSlot.props) {
@@ -70,7 +82,20 @@ export default {
       return (e) => {
         e.preventDefault()
         this.setTab(index)
-        console.log(index)
+      }
+    },
+    onResize (index) {
+      const tabContent = this.$refs.contents?.querySelector('.tab-content-wrapper.-active .tab-content')
+      const tabContentWidth = tabContent.clientWidth
+      const rootWidth = this.$refs.root?.clientWidth
+      const navWidth = this.$refs.nav?.clientWidth
+      const contentsWidth = this.$refs.contents?.clientWidth
+
+
+      if (contentsWidth < tabContentWidth) {
+        this.$emit('tooSmall')
+      } else if (contentsWidth - navWidth >= tabContentWidth){
+        this.$emit('tooBig')
       }
     },
     // DO NOT put it to computed, it doesn't work (caching?)
@@ -85,7 +110,12 @@ export default {
         this.onSwitch.call(null, this.slots()[index].key)
       }
       this.active = index
-      this.$refs.contents.scrollTop = 0
+    },
+    showNav () {
+      this.navMode = false
+    },
+    hideNav () {
+      this.navMode = true
     }
   },
   render () {
@@ -93,7 +123,7 @@ export default {
       .map((slot, index) => {
         const props = slot.props
         if (!props) return
-        const classesTab = ['vertical-tab menu-item']
+        const classesTab = ['vertical-tab', 'menu-item']
         if (this.activeIndex === index) {
           classesTab.push('-active')
         }
@@ -104,6 +134,7 @@ export default {
             class={classesTab.join(' ')}
             type="button"
             role="tab"
+            title={props.label}
           >
             {!props.icon ? '' : (<FAIcon class="tab-icon" size="1x" fixed-width icon={props.icon}/>)}
             <span class="text">
@@ -117,9 +148,9 @@ export default {
       const props = slot.props
       if (!props) return
       const active = this.activeIndex === index
-      const classes = [ active ? 'active' : 'hidden' ]
+      const classes = ['tab-content-wrapper', active ? '-active' : '-hidden' ]
       if (props.fullHeight) {
-        classes.push('full-height')
+        classes.push('-full-height')
       }
       let delayRender = slot.props['delay-render']
       if (delayRender && active) {
@@ -137,17 +168,25 @@ export default {
       )
 
       return (
-        <div ref="contents" class={classes}>
+        <div class={classes} >
           {header}
-          {renderSlot}
+          <div class={ ['tab-content', props['full-width'] ? '-full-width' : null].join(' ') } >
+            {renderSlot}
+          </div>
         </div>
       )
     })
 
+    const rootClasses = ['vertical-tab-switcher']
+    if (this.navMode) {
+      rootClasses.push('-nav-mode')
+      rootClasses.push('-nav-content')
+    }
+
     return (
-      <div ref="root" class="vertical-tab-switcher">
+      <div ref="root" class={ rootClasses.join(' ') }>
         <div
-          class="tabs -navigation-mode -tabs"
+          class="tabs"
           role="tablist"
           ref="nav"
         >
@@ -157,6 +196,7 @@ export default {
           role="tabpanel"
           class={'contents' + (this.scrollableTabs ? ' scrollable-tabs' : '')}
           v-body-scroll-lock={this.bodyScrollLock}
+          ref="contents"
         >
           {contents}
         </div>

src/components/tab_switcher/vertical_tab_switcher.scss

@@ -4,11 +4,13 @@
 
   > .tabs {
     flex: 0 0 auto;
-    overflow: hidden auto;
     flex-direction: column;
+    overflow: hidden auto;
+    white-space: nowrap;
+    text-overflow: ellipsis;
+    width: 15em;
     border-right: 1px solid;
     border-right-color: var(--border);
-    min-width: 10em;
 
     > .menu-item {
       padding: 0.5em 1em;
@@ -21,52 +23,69 @@
   }
 
   > .contents {
-    flex: 1 0 auto;
+    flex: 1 1 auto;
+    overflow-x: hidden;
 
-    .hidden {
-      display: none;
-    }
+    .tab-content {
+      align-self: center;
 
-    .full-height:not(.hidden) {
-      height: 100%;
-      display: flex;
-      flex-direction: column;
+      &:not(.-full-width) {
+        width: 30em;
+      }
 
-      > *:not(.tab-content-label) {
-        flex: 1;
+      &.-full-width {
+        align-self: stretch;
       }
     }
 
-    .tab-content-label {
-      font-size: 1.5em;
-      padding: 0.5em 1em;
-      margin: 0;
-      border-bottom: 1px solid var(--border);
+    .tab-content-wrapper {
+      display: flex;
+      flex-direction: column;
+
+      .tab-content-label {
+        font-size: 1.5em;
+        padding: 0.5em 1em;
+        margin: 0;
+        border-bottom: 1px solid var(--border);
+      }
+
+      &.-hidden {
+        display: none;
+      }
+
+      &.-full-height:not(.-hidden) {
+        height: 100%;
+        display: flex;
+        flex-direction: column;
+
+        > *:not(.tab-content-label) {
+          flex: 1;
+        }
+      }
     }
   }
 
-  > .tabs,
-  > .content {
-    transition: width 2s ease-in;
-  }
+  &.-nav-mode {
+    &.-nav-tabs {
+      > .tabs {
+        width: 100%;
+      }
 
-  &.-tabs {
-    > .tabs {
-      width: 100%;
+      > .nav-content {
+        width: 0%;
+      }
     }
 
-    > .content {
-      width: 0%;
-    }
-  }
+    &.-nav-content {
+      > .tabs {
+        position: absolute;
+        pointer-events: none;
+        opacity: 0;
+      }
 
-  &.-content {
-    > .tabs {
-      width: 0%;
-    }
-
-    > .content {
-      width: 100%;
+      > .nav-content {
+        width: 100%;
+      }
     }
   }
 }