Fix textarea resizing bug (#2182)

* fix textarea resizing issue

* add changelog entry

* prettier

* remove unnecessary aria-hidden

* prettier

docs/pages/resources/changelog.md

@@ -14,6 +14,7 @@ New versions of Shoelace are released as-needed and generally occur when a criti
 
 ## Next
 
+- Fixed a bug in `<sl-textarea>` causing scroll jumping when using `resize="auto"` [#2182]
 - Fixed a bug in `<sl-relative-time>` where the title attribute would show with redundant info [#2184]
 
 ## 2.17.1

src/components/textarea/textarea.component.ts

@@ -46,6 +46,7 @@ export default class SlTextarea extends ShoelaceElement implements ShoelaceFormC
   private resizeObserver: ResizeObserver;
 
   @query('.textarea__control') input: HTMLTextAreaElement;
+  @query('.textarea__size-adjuster') sizeAdjuster: HTMLTextAreaElement;
 
   @state() private hasFocus = false;
   @property() title = ''; // make reactive to pass through
@@ -196,6 +197,8 @@ export default class SlTextarea extends ShoelaceElement implements ShoelaceFormC
 
   private setTextareaHeight() {
     if (this.resize === 'auto') {
+      // This prevents layout shifts. We use `clientHeight` instead of `scrollHeight` to account for if the `<textarea>` has a max-height set on it. In my tests, this has worked fine. Im not aware of any edge cases. [Konnor]
+      this.sizeAdjuster.style.height = `${this.input.clientHeight}px`;
       this.input.style.height = 'auto';
       this.input.style.height = `${this.input.scrollHeight}px`;
     } else {
@@ -370,6 +373,8 @@ export default class SlTextarea extends ShoelaceElement implements ShoelaceFormC
               @focus=${this.handleFocus}
               @blur=${this.handleBlur}
             ></textarea>
+            <!-- This "adjuster" exists to prevent layout shifting. https://github.com/shoelace-style/shoelace/issues/2180 -->
+            <div part="textarea-adjuster" class="textarea__size-adjuster" ?hidden=${this.resize !== 'auto'}></div>
           </div>
         </div>
 

src/components/textarea/textarea.styles.ts

@@ -6,7 +6,7 @@ export default css`
   }
 
   .textarea {
-    display: flex;
+    display: grid;
     align-items: center;
     position: relative;
     width: 100%;
@@ -55,6 +55,17 @@ export default css`
     cursor: not-allowed;
   }
 
+  .textarea__control,
+  .textarea__size-adjuster {
+    grid-area: 1 / 1 / 2 / 2;
+  }
+
+  .textarea__size-adjuster {
+    visibility: hidden;
+    pointer-events: none;
+    opacity: 0;
+  }
+
   .textarea--standard.textarea--disabled .textarea__control {
     color: var(--sl-input-color-disabled);
   }
@@ -87,7 +98,6 @@ export default css`
   }
 
   .textarea__control {
-    flex: 1 1 auto;
     font-family: inherit;
     font-size: inherit;
     font-weight: inherit;