Make all DB engines optional build features

src/db/Cargo.toml

@@ -21,9 +21,9 @@ err-derive = "0.3"
 hexdump = "0.1"
 tracing = "0.1.30"
 
-heed = { version = "0.11", default-features = false, features = ["lmdb"] }
-rusqlite = "0.27"
-sled = "0.34"
+heed = { version = "0.11", default-features = false, features = ["lmdb"], optional = true }
+rusqlite = { version = "0.27", optional = true }
+sled = { version = "0.34", optional = true }
 
 # cli deps
 clap = { version = "3.1.18", optional = true, features = ["derive", "env"] }
@@ -35,3 +35,5 @@ mktemp = "0.4"
 [features]
 bundled-libs = [ "rusqlite/bundled" ]
 cli = ["clap", "pretty_env_logger"]
+lmdb = [ "heed" ]
+sqlite = [ "rusqlite" ]

src/db/lib.rs

@@ -1,8 +1,12 @@
 #[macro_use]
+#[cfg(feature = "sqlite")]
 extern crate tracing;
 
+#[cfg(feature = "lmdb")]
 pub mod lmdb_adapter;
+#[cfg(feature = "sled")]
 pub mod sled_adapter;
+#[cfg(feature = "sqlite")]
 pub mod sqlite_adapter;
 
 pub mod counted_tree_hack;