Show mention picker immediately after @ entered.

app/src/main/java/org/thoughtcrime/securesms/components/ComposeText.java

@@ -102,7 +102,7 @@ protected void onSelectionChanged(int selectionStart, int selectionEnd) {
       if (selectionStart == selectionEnd) {
         doAfterCursorChange(getText());
       } else {
-        updateQuery("");
+        updateQuery(null);
       }
     }
 
@@ -284,18 +284,18 @@ private void doAfterCursorChange(@NonNull Editable text) {
     if (enoughToFilter(text)) {
       performFiltering(text);
     } else {
-      updateQuery("");
+      updateQuery(null);
     }
   }
 
   private void performFiltering(@NonNull Editable text) {
     int          end   = getSelectionEnd();
     int          start = findQueryStart(text, end);
     CharSequence query = text.subSequence(start, end);
-    updateQuery(query);
+    updateQuery(query.toString());
   }
 
-  private void updateQuery(@NonNull CharSequence query) {
+  private void updateQuery(@Nullable String query) {
     if (mentionQueryChangedListener != null) {
       mentionQueryChangedListener.onQueryChanged(query);
     }
@@ -306,7 +306,7 @@ private boolean enoughToFilter(@NonNull Editable text) {
     if (end < 0) {
       return false;
     }
-    return end - findQueryStart(text, end) >= 1;
+    return findQueryStart(text, end) != -1;
   }
 
   public void replaceTextWithMention(@NonNull String displayName, @NonNull RecipientId recipientId) {
@@ -340,7 +340,7 @@ public void replaceTextWithMention(@NonNull String displayName, @NonNull Recipie
 
   private int findQueryStart(@NonNull CharSequence text, int inputCursorPosition) {
     if (inputCursorPosition == 0) {
-      return inputCursorPosition;
+      return -1;
     }
 
     int delimiterSearchIndex = inputCursorPosition - 1;
@@ -351,7 +351,7 @@ private int findQueryStart(@NonNull CharSequence text, int inputCursorPosition)
     if (delimiterSearchIndex >= 0 && text.charAt(delimiterSearchIndex) == MENTION_STARTER) {
       return delimiterSearchIndex + 1;
     }
-    return inputCursorPosition;
+    return -1;
   }
 
   private static class CommitContentListener implements InputConnectionCompat.OnCommitContentListener {
@@ -391,6 +391,6 @@ public interface CursorPositionChangedListener {
   }
 
   public interface MentionQueryChangedListener {
-    void onQueryChanged(CharSequence query);
+    void onQueryChanged(@Nullable String query);
   }
 }

app/src/main/java/org/thoughtcrime/securesms/conversation/ui/mentions/MentionsPickerRepository.java

@@ -4,6 +4,7 @@
 import android.text.TextUtils;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.WorkerThread;
 
 import com.annimon.stream.Stream;
@@ -26,8 +27,8 @@ final class MentionsPickerRepository {
   }
 
   @WorkerThread
-  @NonNull List<Recipient> search(MentionQuery mentionQuery) {
-    if (TextUtils.isEmpty(mentionQuery.query)) {
+  @NonNull List<Recipient> search(@NonNull MentionQuery mentionQuery) {
+    if (mentionQuery.query == null) {
       return Collections.emptyList();
     }
 
@@ -40,10 +41,10 @@ final class MentionsPickerRepository {
   }
 
   static class MentionQuery {
-    private final String                            query;
-    private final List<GroupMemberEntry.FullMember> members;
+    @Nullable private final String                            query;
+    @NonNull  private final List<GroupMemberEntry.FullMember> members;
 
-    MentionQuery(@NonNull String query, @NonNull List<GroupMemberEntry.FullMember> members) {
+    MentionQuery(@Nullable String query, @NonNull List<GroupMemberEntry.FullMember> members) {
       this.query   = query;
       this.members = members;
     }

app/src/main/java/org/thoughtcrime/securesms/conversation/ui/mentions/MentionsPickerViewModel.java

@@ -1,6 +1,7 @@
 package org.thoughtcrime.securesms.conversation.ui.mentions;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 import androidx.lifecycle.Transformations;
@@ -20,22 +21,23 @@
 import org.thoughtcrime.securesms.util.livedata.LiveDataUtil;
 
 import java.util.List;
+import java.util.Objects;
 
 public class MentionsPickerViewModel extends ViewModel {
 
   private final SingleLiveEvent<Recipient>      selectedRecipient;
   private final LiveData<List<MappingModel<?>>> mentionList;
   private final MutableLiveData<LiveGroup>      group;
-  private final MutableLiveData<String>         liveQuery;
+  private final MutableLiveData<Query>          liveQuery;
 
   MentionsPickerViewModel(@NonNull MentionsPickerRepository mentionsPickerRepository) {
     group             = new MutableLiveData<>();
-    liveQuery         = new MutableLiveData<>();
+    liveQuery         = new MutableLiveData<>(Query.NONE);
     selectedRecipient = new SingleLiveEvent<>();
 
     LiveData<List<FullMember>> fullMembers  = Transformations.distinctUntilChanged(Transformations.switchMap(group, LiveGroup::getFullMembers));
-    LiveData<String>           query        = Transformations.distinctUntilChanged(liveQuery);
-    LiveData<MentionQuery>     mentionQuery = LiveDataUtil.combineLatest(query, fullMembers, MentionQuery::new);
+    LiveData<Query>            query        = Transformations.distinctUntilChanged(liveQuery);
+    LiveData<MentionQuery>     mentionQuery = LiveDataUtil.combineLatest(query, fullMembers, (q, m) -> new MentionQuery(q.query, m));
 
     mentionList = LiveDataUtil.mapAsync(mentionQuery, q -> Stream.of(mentionsPickerRepository.search(q)).<MappingModel<?>>map(MentionViewState::new).toList());
   }
@@ -52,8 +54,8 @@ void onSelectionChange(@NonNull Recipient recipient) {
     return selectedRecipient;
   }
 
-  public void onQueryChange(@NonNull CharSequence query) {
-    liveQuery.setValue(query.toString());
+  public void onQueryChange(@Nullable String query) {
+    liveQuery.setValue(query == null ? Query.NONE : new Query(query));
   }
 
   public void onRecipientChange(@NonNull Recipient recipient) {
@@ -64,6 +66,39 @@ public void onRecipientChange(@NonNull Recipient recipient) {
     }
   }
 
+  /**
+   * Wraps a nullable query string so it can be properly propagated through
+   * {@link LiveDataUtil#combineLatest(LiveData, LiveData, LiveDataUtil.Combine)}.
+   */
+  private static class Query {
+    static final Query NONE = new Query(null);
+
+    @Nullable private final String query;
+
+    Query(@Nullable String query) {
+      this.query = query;
+    }
+
+    @Override
+    public boolean equals(Object object) {
+      if (this == object) {
+        return true;
+      }
+
+      if (object == null || getClass() != object.getClass()) {
+        return false;
+      }
+
+      Query other = (Query) object;
+      return Objects.equals(query, other.query);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(query);
+    }
+  }
+
   public static final class Factory implements ViewModelProvider.Factory {
     @Override
     public @NonNull <T extends ViewModel> T create(@NonNull Class<T> modelClass) {

app/src/main/java/org/thoughtcrime/securesms/database/RecipientDatabase.java

@@ -1938,10 +1938,6 @@ public void updateSystemContactColors(@NonNull ColorUpdater updater) {
   }
 
   public @NonNull List<Recipient> queryRecipientsForMentions(@NonNull String query, @Nullable List<RecipientId> recipientIds) {
-    if (TextUtils.isEmpty(query)) {
-      return Collections.emptyList();
-    }
-
     query = buildCaseInsensitiveGlobPattern(query);
 
     String ids = null;