Cleanup remaining use of Result<bool, Error> (fixes #4862)

crates/api_crud/src/user/create.rs

@@ -107,9 +107,7 @@ pub async fn register(
   check_slurs(&data.username, &slur_regex)?;
   check_slurs_opt(&data.answer, &slur_regex)?;
 
-  if Person::is_username_taken(&mut context.pool(), &data.username).await? {
-    return Err(LemmyErrorType::UsernameAlreadyExists)?;
-  }
+  Person::check_username_taken(&mut context.pool(), &data.username).await?;
 
   if let Some(email) = &data.email {
     LocalUser::check_is_email_taken(&mut context.pool(), email).await?;
@@ -329,9 +327,7 @@ pub async fn authenticate_with_oauth(
       check_slurs(username, &slur_regex)?;
       check_slurs_opt(&data.answer, &slur_regex)?;
 
-      if Person::is_username_taken(&mut context.pool(), username).await? {
-        return Err(LemmyErrorType::UsernameAlreadyExists)?;
-      }
+      Person::check_username_taken(&mut context.pool(), username).await?;
 
       // We have to create a person, a local_user, and an oauth_account
       person = create_person(

crates/db_schema/src/impls/person.rs

@@ -21,6 +21,7 @@ use diesel::{
   QueryDsl,
 };
 use diesel_async::RunQueryDsl;
+use lemmy_utils::{error::LemmyResult, LemmyErrorType};
 
 #[async_trait]
 impl Crud for Person {
@@ -121,16 +122,18 @@ impl Person {
       .await
   }
 
-  pub async fn is_username_taken(pool: &mut DbPool<'_>, username: &str) -> Result<bool, Error> {
+  pub async fn check_username_taken(pool: &mut DbPool<'_>, username: &str) -> LemmyResult<()> {
     use diesel::dsl::{exists, select};
     let conn = &mut get_conn(pool).await?;
-    select(exists(
+    select(not(exists(
       person::table
         .filter(lower(person::name).eq(username.to_lowercase()))
         .filter(person::local.eq(true)),
-    ))
-    .get_result(conn)
-    .await
+    )))
+    .get_result::<bool>(conn)
+    .await?
+    .then_some(())
+    .ok_or(LemmyErrorType::UsernameAlreadyExists.into())
   }
 }