SearchBackend: add Auto variant as default

src/components/mail/status.rs

@@ -370,8 +370,12 @@ impl Component for AccountStatus {
                 a.settings.conf.search_backend(),
                 a.backend_capabilities.supports_search,
             ) {
-                (SearchBackend::None, true) => "backend-side search".to_string(),
+                (SearchBackend::Auto, true) | (SearchBackend::None, true) => {
-                (SearchBackend::None, false) => "none (search will be slow)".to_string(),
+                    "backend-side search".to_string()
+                }
+                (SearchBackend::Auto, false) | (SearchBackend::None, false) => {
+                    "none (search will be slow)".to_string()
+                }
                 #[cfg(feature = "sqlite3")]
                 (SearchBackend::Sqlite3, _) => {
                     if let Ok(path) = crate::sqlite3::db_path() {

src/conf.rs

@@ -621,23 +621,17 @@ impl Serialize for IndexStyle {
     }
 }
 
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Copy, Clone, PartialEq)]
 pub enum SearchBackend {
     None,
+    Auto,
     #[cfg(feature = "sqlite3")]
     Sqlite3,
 }
 
 impl Default for SearchBackend {
     fn default() -> Self {
-        #[cfg(feature = "sqlite3")]
+        SearchBackend::Auto
-        {
-            SearchBackend::Sqlite3
-        }
-        #[cfg(not(feature = "sqlite3"))]
-        {
-            SearchBackend::None
-        }
     }
 }
 
@@ -649,8 +643,14 @@ impl<'de> Deserialize<'de> for SearchBackend {
         let s = <String>::deserialize(deserializer)?;
         match s.as_str() {
             #[cfg(feature = "sqlite3")]
-            "sqlite3" => Ok(SearchBackend::Sqlite3),
+            sqlite3 if sqlite3.eq_ignore_ascii_case("sqlite3") => Ok(SearchBackend::Sqlite3),
-            "nothing" | "none" | "" => Ok(SearchBackend::None),
+            none if none.eq_ignore_ascii_case("none")
+                || none.eq_ignore_ascii_case("nothing")
+                || none.is_empty() =>
+            {
+                Ok(SearchBackend::None)
+            }
+            auto if auto.eq_ignore_ascii_case("auto") => Ok(SearchBackend::Auto),
             _ => Err(de::Error::custom("invalid `search_backend` value")),
         }
     }
@@ -665,6 +665,7 @@ impl Serialize for SearchBackend {
             #[cfg(feature = "sqlite3")]
             SearchBackend::Sqlite3 => serializer.serialize_str("sqlite3"),
             SearchBackend::None => serializer.serialize_str("none"),
+            SearchBackend::Auto => serializer.serialize_str("auto"),
         }
     }
 }

src/conf/accounts.rs

@@ -437,8 +437,19 @@ impl Account {
             }
         };
 
-        if ["imap", "jmap", "notmuch"].contains(&settings.account().format()) {
+        if settings.conf.search_backend == crate::conf::SearchBackend::Auto {
-            settings.conf.search_backend = crate::conf::SearchBackend::None;
+            if backend.capabilities().supports_search {
+                settings.conf.search_backend = crate::conf::SearchBackend::None;
+            } else {
+                #[cfg(feature = "sqlite3")]
+                {
+                    settings.conf.search_backend = crate::conf::SearchBackend::Sqlite3;
+                }
+                #[cfg(not(feature = "sqlite3"))]
+                {
+                    settings.conf.search_backend = crate::conf::SearchBackend::None;
+                }
+            }
         }
 
         let mut active_jobs = HashMap::default();
@@ -1433,7 +1444,7 @@ impl Account {
         match self.settings.conf.search_backend {
             #[cfg(feature = "sqlite3")]
             crate::conf::SearchBackend::Sqlite3 => crate::sqlite3::search(&query, _sort),
-            crate::conf::SearchBackend::None => {
+            crate::conf::SearchBackend::Auto | crate::conf::SearchBackend::None => {
                 if self.backend_capabilities.supports_search {
                     self.backend
                         .read()