feat(textarea): textarea shrinking and resizing

* Changes the textarea behavior to consider the "rows" attribute as the minimum, instead of the maximum, when auto-expanding the element.
* Adds a handle for vertically resizing the textarea element.
* Simplifies the logic for determining the textarea height.
* Makes the textarea sizing more accurate by using scrollHeight directly, instead of depending on the line height and amount of rows.
* Avoids potential issues where the textarea wouldn't resize when adding a newline.

Closes #7649.

BREAKING CHANGE
This changes the behavior from considering the "rows" attribute as the maximum to considering it as the minimum.

src/components/input/input-theme.scss

@@ -35,10 +35,14 @@ md-input-container.md-THEME_NAME-theme {
         color: '{{foreground-2}}';
       }
     }
-    &.md-input-focused {
+    &.md-input-focused,
+    &.md-input-resized {
       .md-input {
         border-color: '{{primary-color}}';
       }
+    }
+
+    &.md-input-focused {
       label {
         color: '{{primary-color}}';
       }

src/components/input/input.js

@@ -169,6 +169,7 @@ function labelDirective() {
  * @param {string=} placeholder An alternative approach to using aria-label when the label is not
  *   PRESENT. The placeholder text is copied to the aria-label attribute.
  * @param md-no-autogrow {boolean=} When present, textareas will not grow automatically.
+ * @param md-no-resize {boolean=} Disables the textarea resize handle.
  * @param md-no-asterisk {boolean=} When present, asterisk will not be appended to required inputs label
  * @param md-detect-hidden {boolean=} When present, textareas will be sized properly when they are
  *   revealed after being hidden. This is off by default for performance reasons because it
@@ -255,9 +256,20 @@ function labelDirective() {
  * error animation effects. Therefore, it is *not* advised to use the Layout system inside of the
  * `<md-input-container>` tags. Instead, use relative or absolute positioning.
  *
+ *
+ * <h3>Textarea directive</h3>
+ * The `textarea` element within a `md-input-container` has the following specific behavior:
+ * - By default the `textarea` grows as the user types. This can be disabled via the `md-no-autogrow`
+ * attribute.
+ * - If a `textarea` has the `rows` attribute, it will treat the `rows` as the minimum height and will
+ * continue growing as the user types. For example a textarea with `rows="3"` will be 3 lines of text
+ * high initially. If no rows are specified, the directive defaults to 1.
+ * - The textarea's bottom border acts as a handle which users can drag, in order to resize the element vertically.
+ * Once the user has resized a `textarea`, the autogrowing functionality becomes disabled. If you don't want a
+ * `textarea` to be resizeable by the user, you can add the `md-no-resize` attribute.
  */
 
-function inputTextareaDirective($mdUtil, $window, $mdAria, $timeout) {
+function inputTextareaDirective($mdUtil, $window, $mdAria, $timeout, $mdGesture) {
   return {
     restrict: 'E',
     require: ['^?mdInputContainer', '?ngModel'],
@@ -375,9 +387,11 @@ function inputTextareaDirective($mdUtil, $window, $mdAria, $timeout) {
     }
 
     function setupTextarea() {
-      if (attr.hasOwnProperty('mdNoAutogrow')) {
-        return;
-      }
+      var isAutogrowing = !attr.hasOwnProperty('mdNoAutogrow');
+
+      attachResizeHandle();
+
+      if (!isAutogrowing) return;
 
       // Can't check if height was or not explicity set,
       // so rows attribute will take precedence if present
@@ -391,78 +405,138 @@ function inputTextareaDirective($mdUtil, $window, $mdAria, $timeout) {
         $mdUtil.nextTick(growTextarea);
       }, 10, false);
 
-      // We can hook into Angular's pipeline, instead of registering a new listener.
-      // Note that we should use `$parsers`, as opposed to `$viewChangeListeners` which
-      // was used before, because `$viewChangeListeners` don't fire if the input is
-      // invalid.
+      // We could leverage ngModel's $parsers here, however it
+      // isn't reliable, because Angular trims the input by default,
+      // which means that growTextarea won't fire when newlines and
+      // spaces are added.
+      element.on('input', growTextarea);
+
+      // We should still use the $formatters, because they fire when
+      // the value was changed from outside the textarea.
       if (hasNgModel) {
-        ngModelCtrl.$formatters.unshift(pipelineListener);
-        ngModelCtrl.$parsers.unshift(pipelineListener);
-      } else {
-        // Note that it's safe to use the `input` event since we're not supporting IE9 and below.
-        element.on('input', growTextarea);
+        ngModelCtrl.$formatters.push(formattersListener);
       }
 
       if (!minRows) {
-        element
-          .attr('rows', 1)
-          .on('scroll', onScroll);
+        element.attr('rows', 1);
       }
 
       angular.element($window).on('resize', growTextarea);
-
-      scope.$on('$destroy', function() {
-        angular.element($window).off('resize', growTextarea);
-      });
+      scope.$on('$destroy', disableAutogrow);
 
       function growTextarea() {
         // temporarily disables element's flex so its height 'runs free'
         element
-          .addClass('md-no-flex')
-          .attr('rows', 1);
-
-        if (minRows) {
-          if (!lineHeight) {
-            node.style.minHeight = 0;
-            lineHeight = element.prop('clientHeight');
-            node.style.minHeight = null;
-          }
+          .attr('rows', 1)
+          .css('height', 'auto')
+          .addClass('md-no-flex');
+
+        var height = getHeight();
 
-          var newRows = Math.round( Math.round(getHeight() / lineHeight) );
-          var rowsToSet = Math.min(newRows, minRows);
+        if (!lineHeight) {
+          lineHeight = element.prop('offsetHeight');
+        }
 
-          element
-            .css('height', lineHeight * rowsToSet + 'px')
-            .attr('rows', rowsToSet)
-            .toggleClass('_md-textarea-scrollable', newRows >= minRows);
+        if (minRows && lineHeight) {
+          height = Math.max(height, lineHeight * minRows);
+        }
 
-        } else {
-          element.css('height', 'auto');
-          node.scrollTop = 0;
-          var height = getHeight();
-          if (height) element.css('height', height + 'px');
+        if (lineHeight) {
+          element.attr('rows', Math.round(height / lineHeight));
         }
 
-        element.removeClass('md-no-flex');
+        element
+          .css('height', height + 'px')
+          .removeClass('md-no-flex');
       }
 
       function getHeight() {
         var offsetHeight = node.offsetHeight;
         var line = node.scrollHeight - offsetHeight;
-        return offsetHeight + (line > 0 ? line : 0);
+        return offsetHeight + Math.max(line, 0);
       }
 
-      function onScroll(e) {
-        node.scrollTop = 0;
-        // for smooth new line adding
-        var line = node.scrollHeight - node.offsetHeight;
-        var height = node.offsetHeight + line;
-        node.style.height = height + 'px';
+      function formattersListener(value) {
+        $mdUtil.nextTick(growTextarea);
+        return value;
       }
 
-      function pipelineListener(value) {
-        growTextarea();
-        return value;
+      function disableAutogrow() {
+        if (!isAutogrowing) return;
+
+        isAutogrowing = false;
+        angular.element($window).off('resize', growTextarea);
+        element
+          .attr('md-no-autogrow', '')
+          .off('input', growTextarea);
+
+        if (hasNgModel) {
+          var listenerIndex = ngModelCtrl.$formatters.indexOf(formattersListener);
+
+          if (listenerIndex > -1) {
+            ngModelCtrl.$formatters.splice(listenerIndex, 1);
+          }
+        }
+      }
+
+      function attachResizeHandle() {
+        if (attr.hasOwnProperty('mdNoResize')) return;
+
+        var handle = angular.element('<div class="md-resize-handle"></div>');
+        var isDragging = false;
+        var dragStart = null;
+        var startHeight = 0;
+        var container = containerCtrl.element;
+        var dragGestureHandler = $mdGesture.register(handle, 'drag', { horizontal: false });
+
+        element.after(handle);
+        handle.on('mousedown', onMouseDown);
+
+        container
+          .on('$md.dragstart', onDragStart)
+          .on('$md.drag', onDrag)
+          .on('$md.dragend', onDragEnd);
+
+        scope.$on('$destroy', function() {
+          handle
+            .off('mousedown', onMouseDown)
+            .remove();
+
+          container
+            .off('$md.dragstart', onDragStart)
+            .off('$md.drag', onDrag)
+            .off('$md.dragend', onDragEnd);
+
+          dragGestureHandler();
+          handle = null;
+          container = null;
+          dragGestureHandler = null;
+        });
+
+        function onMouseDown(ev) {
+          ev.preventDefault();
+          isDragging = true;
+          dragStart = ev.clientY;
+          startHeight = parseFloat(element.css('height')) || element.prop('offsetHeight');
+        }
+
+        function onDragStart(ev) {
+          if (!isDragging) return;
+          ev.preventDefault();
+          disableAutogrow();
+          container.addClass('md-input-resized');
+        }
+
+        function onDrag(ev) {
+          if (!isDragging) return;
+          element.css('height', startHeight + (ev.pointer.y - dragStart) + 'px');
+        }
+
+        function onDragEnd(ev) {
+          if (!isDragging) return;
+          isDragging = false;
+          container.removeClass('md-input-resized');
+        }
       }
 
       // Attach a watcher to detect when the textarea gets shown.

src/components/input/input.scss

@@ -24,6 +24,8 @@ $icon-top-offset: ($icon-offset - $input-padding-top - $input-border-width-focus
 
 $icon-float-focused-top: -8px !default;
 
+$input-resize-handle-height: 10px !default;
+
 md-input-container {
   @include pie-clearfix();
   display: inline-block;
@@ -46,6 +48,16 @@ md-input-container {
     min-width: 1px;
   }
 
+  .md-resize-handle {
+    position: absolute;
+    bottom: $input-error-height - $input-border-width-default * 2;
+    left: 0;
+    height: $input-resize-handle-height;
+    background: transparent;
+    width: 100%;
+    cursor: ns-resize;
+  }
+
   > md-icon {
     position: absolute;
     top: $icon-top-offset;
@@ -88,14 +100,10 @@ md-input-container {
       -ms-flex-preferred-size: auto; //IE fix
     }
 
-    &._md-textarea-scrollable,
-    &[md-no-autogrow] {
-      overflow: auto;
-    }
-
     // The height usually gets set to 1 line by `.md-input`.
     &[md-no-autogrow] {
       height: auto;
+      overflow: auto;
     }
   }
 
@@ -299,7 +307,8 @@ md-input-container {
 
   // Use wide border in error state or in focused state
   &.md-input-focused .md-input,
-  .md-input.ng-invalid.ng-dirty {
+  .md-input.ng-invalid.ng-dirty,
+  &.md-input-resized .md-input {
     padding-bottom: 0; // Increase border width by 1px, decrease padding by 1
     border-width: 0 0 $input-border-width-focused 0;
   }