2 files changed, 59 insertions, 1 deletions
diff --git a/addons/mail/static/src/models/thread_view/thread_view.js b/addons/mail/static/src/models/thread_view/thread_view.js
index 0c6cdf6d458..f381f3d86f9 100644
--- a/addons/mail/static/src/models/thread_view/thread_view.js
+++ b/addons/mail/static/src/models/thread_view/thread_view.js
@@ -80,6 +80,21 @@ function factory(dependencies) {
          * @private
          * @returns {integer|undefined}
          */
+        _computeThreadCacheInitialScrollHeight() {
+            if (!this.threadCache) {
+                return clear();
+            }
+            const threadCacheInitialScrollHeight = this.threadCacheInitialScrollHeights[this.threadCache.localId];
+            if (threadCacheInitialScrollHeight !== undefined) {
+                return threadCacheInitialScrollHeight;
+            }
+            return clear();
+        }
+
+        /**
+         * @private
+         * @returns {integer|undefined}
+         */
         _computeThreadCacheInitialScrollPosition() {
             if (!this.threadCache) {
                 return clear();
@@ -264,6 +279,13 @@ function factory(dependencies) {
             inverse: 'threadViews',
             related: 'threadViewer.threadCache',
         }),
+        threadCacheInitialScrollHeight: attr({
+            compute: '_computeThreadCacheInitialScrollHeight',
+            dependencies: [
+                'threadCache',
+                'threadCacheInitialScrollHeights',
+            ],
+        }),
         threadCacheInitialScrollPosition: attr({
             compute: '_computeThreadCacheInitialScrollPosition',
             dependencies: [
@@ -278,6 +300,13 @@ function factory(dependencies) {
             related: 'threadCache.isLoading',
         }),
         /**
+         * List of saved initial scroll heights of thread caches.
+         */
+        threadCacheInitialScrollHeights: attr({
+            default: {},
+            related: 'threadViewer.threadCacheInitialScrollHeights',
+        }),
+        /**
          * List of saved initial scroll positions of thread caches.
          */
         threadCacheInitialScrollPositions: attr({
diff --git a/addons/mail/static/src/models/thread_view/thread_viewer.js b/addons/mail/static/src/models/thread_view/thread_viewer.js
index 3c643339eff..1e48e4ad805 100644
--- a/addons/mail/static/src/models/thread_view/thread_viewer.js
+++ b/addons/mail/static/src/models/thread_view/thread_viewer.js
@@ -13,7 +13,27 @@ function factory(dependencies) {
         //----------------------------------------------------------------------
 
         /**
-         * @param {string} scrollTop
+         * @param {integer} scrollHeight
+         */
+        saveThreadCacheScrollHeightAsInitial(scrollHeight) {
+            if (!this.threadCache) {
+                return;
+            }
+            if (this.chatter) {
+                // Initial scroll height is disabled for chatter because it is
+                // too complex to handle correctly and less important
+                // functionally.
+                return;
+            }
+            this.update({
+                threadCacheInitialScrollHeights: Object.assign({}, this.threadCacheInitialScrollHeights, {
+                    [this.threadCache.localId]: scrollHeight,
+                }),
+            });
+        }
+
+        /**
+         * @param {integer} scrollTop
          */
         saveThreadCacheScrollPositionsAsInitial(scrollTop) {
             if (!this.threadCache) {
@@ -231,6 +251,15 @@ function factory(dependencies) {
             ],
         }),
         /**
+         * Determines the initial scroll height of thread caches, which is the
+         * scroll height at the time the last scroll position was saved.
+         * Useful to only restore scroll position when the corresponding height
+         * is available, otherwise the restore makes no sense.
+         */
+        threadCacheInitialScrollHeights: attr({
+            default: {},
+        }),
+        /**
          * Determines the initial scroll positions of thread caches.
          * Useful to restore scroll position on changing back to this
          * thread cache. Note that this is only applied when opening