Resolve feature dependency tree

tower/Cargo.toml

@@ -26,35 +26,36 @@ edition = "2018"
 [features]
 default = ["log"]
 log = ["tracing/log"]
-balance = ["discover", "load", "ready-cache", "make"]
-buffer = []
+balance = ["discover", "load", "ready-cache", "make", "rand", "slab"]
+buffer = ["tokio/sync", "tokio/rt-core"]
 discover = []
 filter = []
-hedge = ["filter"]
-limit = []
-load = ["discover"]
+hedge = ["filter", "futures-util", "hdrhistogram", "tokio/time"]
+limit = ["tokio/time"]
+load = ["discover", "tokio/time"]
 load-shed = []
-make = []
-ready-cache = []
-reconnect = ["make"]
-retry = []
-spawn-ready = []
-timeout = []
-util = []
+make = ["tokio/io-std"]
+ready-cache = ["futures-util", "indexmap", "tokio/sync"]
+reconnect = ["make", "tokio/io-std"]
+retry = ["tokio/time"]
+spawn-ready = ["futures-util", "tokio/sync", "tokio/rt-core"]
+timeout = ["tokio/time"]
+util = ["futures-util"]
 
 [dependencies]
 futures-core = "0.3"
-futures-util = { version = "0.3", default-features = false, features = ["alloc"] }
-hdrhistogram = "6.0"
-indexmap = "1.0.2"
 pin-project = "0.4"
-rand = { version = "0.7", features = ["small_rng"] }
-slab = "0.4"
-tokio = { version = "0.2", features = ["rt-core", "sync", "time"] }
 tower-layer = { version = "0.3", path = "../tower-layer" }
 tower-service = { version = "0.3", path = "../tower-service" }
 tracing = "0.1.2"
 
+futures-util = { version = "0.3", default-features = false, features = ["alloc"], optional = true }
+hdrhistogram = { version = "6.0", optional = true }
+indexmap = { version = "1.0.2", optional = true }
+rand = { version = "0.7", features = ["small_rng"], optional = true }
+slab = { version = "0.4", optional = true }
+tokio = { version = "0.2", optional = true }
+
 [dev-dependencies]
 futures-util = { version = "0.3", default-features = false, features = ["alloc"] }
 hdrhistogram = "6.0"