trident.cli Getting Started

In a tools.deps workflow, you normally install build tasks by adding them to your deps.edn file as aliases. But this has a couple downsides:

• If you want to use the same set of aliases in different projects, you have to duplicate them in both deps.edn files. You could put the aliases in your user deps.edn file, but then they won't be available to other developers.

• Every time you run an alias, you'll have to wait for JVM startup and Clojure compilation.

I solve these problems like so:

• Instead of storing the set of build tasks in deps.edn, I put it in a library. The library has dependencies to all the build tasks I want, and for convenience, it includes a main fn has the build tasks as subcommands.

• I start an nRepl server with the above library loaded. All build commands are executed through this server.

Example

The normal way

Execute these commands:

mkdir myproject
cd myproject
mkdir -p src/myproject/
cat > src/myproject/core.clj << EOD
(ns myproject.core)

(defn foo [a b]
  (+ a b))
EOD
cat > deps.edn << EOD
{:aliases
 {:new {:extra-deps {seancorfield/clj-new {:mvn/version "0.5.5"}}
        :main-opts ["-m" "clj-new.create"]}
  :jar {:extra-deps {luchiniatwork/cambada {:mvn/version "1.0.0"}}
        :main-opts ["-m" "cambada.jar"]}}}
EOD
time clj -Ajar --help

For me, time clj -Ajar --help took about 11 seconds.

The Trident way

Now execute these commands:

mkdir myproject2
cd myproject2
mkdir -p src/myproject/
cat > src/myproject/core.clj << EOD
(ns myproject.core)

(defn foo [a b]
  (+ a b))
EOD
echo '{:aliases {:build {:extra-deps {build {:local/root "build"}}}}}' > deps.edn
mkdir build
cat > build/deps.edn << EOD
{:deps {trident/cli {:mvn/version "0.1.5"}
        nrepl {:mvn/version "0.6.0"}
        seancorfield/clj-new {:mvn/version "0.5.5"}
        luchiniatwork/cambada {:mvn/version "1.0.0"}}}
EOD
mkdir -p build/src/myproject
cat > build/src/myproject/build.clj << EOD
(ns myproject.build
  (:require [trident.cli :refer [defmain]]
            [clj-new.create :as create]
            [cambada.jar :as jar]))

(def cli {:subcommands {"new" #'create/-main
                        "jar" #'jar/-main}})
(defmain cli)
EOD
clj -Abuild -e "(do (require 'myproject.build)
                    (require '[nrepl.server :refer [start-server]])
                    (start-server :port 7888))"

So we've created a separate build project and started a build server. Now we need an nRepl client. Install Grenchman. If there aren't binaries available for your system, you can use trepl.py instead.

After you see the output from start-server, run these commands in another terminal:

alias build='GRENCH_PORT=7888 grench main trident.cli.util/-main "$PWD" myproject.build/-main'
# Use this instead if you're using trepl.py:
#alias build='trepl.py -p 7888 main trident.cli.util/-main "$PWD" myproject.build/-main'

build --help
time build jar --help

Ta-da. That's the essence of my approach to building.

Details

To reiterate--the main idea here (in addition to using a repl to avoid startup time) is that we're pushing as much as we can out of deps.edn and into a separate, single library. That way, our build library can be easily shared: we can use all the infrastructure that's already in place for sharing Clojure code.

A few notes:

• trident.cli.util/-main uses the JNR to change the process's current working directory, hence the "$PWD". So the build task will run in whatever directory you call it from.

• trident.cli.util/-main also disables calls to System/exit and shutdown-agents.

• Caveat: deps.edn aliases are good for build tasks that need different classpaths, e.g. if you want to run tests with different versions of Clojure. The trident.cli approach doesn't handle that well.

For more details and examples, see trident/cli and trident/build.