dependency management

Author: RalfJung

Cargo.toml

@@ -40,12 +40,15 @@ rustc_version = { version = "0.2.3", optional = true }
 env_logger = "0.6"
 log = "0.4"
 shell-escape = "0.1.4"
+hex = "0.3.2"
+rand = "0.6"
 # A noop dependency that changes in the Rust repository, it's a bit of a hack.
 # See the `src/tools/rustc-workspace-hack/README.md` file in `rust-lang/rust`
 # for more information.
 rustc-workspace-hack = "1.0.0"
-hex = "0.3.2"
-rand = "0.6"
+# Depend on num-traits with default features to avoid having to rebuild
+# between "cargo build" and "cargo intall".
+num-traits = "*"
 
 [build-dependencies]
 vergen = "3"