properly refocus tag from tag selector on re-enter (#4035)

- do not erase the last recorded tag on blur of the tag selector
- on tab from collectionTree or shift-tab from tag selector input,
try to refocus that last focused tag. If one does not exist,
try to focus the first non-disabled tag.

Fixes: #4008

chrome/content/zotero/components/tagSelector/tagSelectorList.jsx

@@ -224,6 +224,36 @@ class TagList extends React.PureComponent {
 		);
 	};
 
+	tagSelectorList() {
+		return document.querySelector('.tag-selector-list');
+	}
+
+	isEmpty() {
+		return !this.tagSelectorList().querySelector('.tag-selector-item:not(.disabled)');
+	}
+
+	clearRecordedFocusedTag() {
+		this.lastFocusedTagIndex = null;
+		this.focusedTagIndex = null;
+	}
+
+	// Focus the last focused tag from the list. If there is none, focus the first
+	// non-disabled tag.
+	async focus() {
+		if (this.focusedTagIndex === null) {
+			let enabledTag = this.tagSelectorList().querySelector('.tag-selector-item:not(.disabled)');
+			if (!enabledTag) return;
+			enabledTag.focus();
+			return;
+		}
+		let tagRefocused = this.refocusTag();
+		if (tagRefocused) return;
+		// If the tag could not be refocused, it means it was removed due to windowing,
+		// so we need to scroll to it.
+		this.setState({ scrollToCell: this.focusedTagIndex });
+		await this.waitForSectionRender();
+	}
+
 	// Try to refocus a focused tag that was removed due to windowing
 	refocusTag() {
 		let tagsList = document.querySelector('.tag-selector-list');
@@ -232,7 +262,9 @@ class TagList extends React.PureComponent {
 		let nodeToFocus = tagsNodes.find(node => node.textContent == tagToFocus.name);
 		if (nodeToFocus) {
 			nodeToFocus.focus();
+			return true;
 		}
+		return false;
 	}
 
 	waitForSectionRender() {
@@ -266,15 +298,6 @@ class TagList extends React.PureComponent {
 		}
 	};
 
-	handleBlur = (event) => {
-		// If the focus leaves the tags list, clear the last focused tag index
-		let tagsList = document.querySelector('.tag-selector-list');
-		if (!tagsList.contains(event.relatedTarget)) {
-			this.focusedTagIndex = null;
-			this.lastFocusedTagIndex = null;
-		}
-	};
-
 	async handleKeyDown(e) {
 		if (!["ArrowRight", "ArrowLeft"].includes(e.key)) return;
 		// If the windowing kicks in, the node of the initially-focused tag may not
@@ -346,7 +369,7 @@ class TagList extends React.PureComponent {
 		}
 		
 		return (
-			<div className="tag-selector-list-container" onBlur={this.handleBlur} onKeyDown={this.handleKeyDown.bind(this)}>
+			<div className="tag-selector-list-container" onKeyDown={this.handleKeyDown.bind(this)}>
 				{tagList}
 			</div>
 		);

chrome/content/zotero/containers/tagSelectorContainer.jsx

@@ -81,6 +81,14 @@ Zotero.TagSelector = class TagSelectorContainer extends React.PureComponent {
 		this.searchBoxRef.current.focus();
 	}
 
+	focusTagList() {
+		this.tagListRef.current.focus();
+	}
+
+	isTagListEmpty() {
+		return this.tagListRef.current.isEmpty();
+	}
+
 	componentDidCatch(error, info) {
 		// Async operations might attempt to update the react components
 		// after window close in tests, which will cause unnecessary crashing.
@@ -100,6 +108,12 @@ Zotero.TagSelector = class TagSelectorContainer extends React.PureComponent {
 			this.prevTreeViewID = this.collectionTreeRow.id;
 		}
 	}
+
+	getSnapshotBeforeUpdate(_) {
+		// Clear the focused tag's record if the props change
+		this.tagListRef.current.clearRecordedFocusedTag();
+		return null;
+	}
 	
 	// Update trigger #1 (triggered by ZoteroPane)
 	async onItemViewChanged({ collectionTreeRow, libraryID }) {
@@ -528,7 +542,6 @@ Zotero.TagSelector = class TagSelectorContainer extends React.PureComponent {
 			searchString={this.state.searchString}
 			dragObserver={this.dragObserver}
 			onSelect={this.handleTagSelected}
-			onKeyDown={this.handleKeyDown}
 			onTagContext={this.handleTagContext}
 			onSearch={this.handleSearch}
 			onSettings={this.handleSettings.bind(this)}

chrome/content/zotero/zoteroPane.js

@@ -420,11 +420,11 @@ var ZoteroPane = new function()
 							return document.getElementById('zotero-tb-add');
 						}
 						// If tag selector is collapsed, go to "New item" button, otherwise focus tag selector
-						let firstNonDisabledTag = tagSelector.querySelector('.tag-selector-item:not(.disabled)');
-						if (firstNonDisabledTag) {
-							return firstNonDisabledTag;
+						if (ZoteroPane.tagSelector.isTagListEmpty()) {
+							return tagSelector.querySelector(".search-input");
 						}
-						return tagSelector.querySelector(".search-input");
+						ZoteroPane.tagSelector.focusTagList();
+						return null;
 					},
 					Escape: clearCollectionSearch
 				}
@@ -446,11 +446,11 @@ var ZoteroPane = new function()
 				'search-input': {
 					Tab: () => tagSelector.querySelector('.tag-selector-actions'),
 					ShiftTab: () => {
-						let firstNonDisabledTag = tagSelector.querySelector('.tag-selector-item:not(.disabled)');
-						if (firstNonDisabledTag) {
-							return firstNonDisabledTag;
+						if (ZoteroPane.tagSelector.isTagListEmpty()) {
+							return document.getElementById("collection-tree");
 						}
-						return document.getElementById("collection-tree");
+						ZoteroPane.tagSelector.focusTagList();
+						return null;
 					},
 				},
 				'tag-selector-item': {