Running build tasks quickly with trepl.py

If you run all your build tasks with clj -m some.namespace ..., you'll have to wait for JVM startup and, more importantly, Clojure compilation every time. As of writing, a simple (require 'trident.build) in a fresh repl takes about 15 seconds (sorry!). That's mainly because trident.build requires a lot of stuff, but even more minimal build task namespaces will still take several seconds to load.

I handle this the same way we handle repl startup time in general: open a repl with dependencies to all the build tasks you need, use that for running build tasks, and don't close the repl.

Because it would be inconvenient to type (-main "some-command" "arg1" ...) all the time, I have written trepl.py, a simple script which can run build tasks from a bash (or whatever) shell over nRepl.

$ trepl.py -h
usage: trepl.py [-h] [-p PORT] [-v] {eval,main} ...

Run some code in an nRepl connection.

positional arguments:
  {eval,main}
    eval                Eval some code.
    main                Run an existing function. Requires trident.cli
                        namespace.

optional arguments:
  -h, --help            show this help message and exit
  -p PORT, --port PORT  The nRepl port. If unspecified, will attempt to read
                        port from an .nrepl-port file (either in the current
                        directory or in an ancestor directory).
  -v, --verbose         Print messages to and from nrepl.

$ trepl.py main -h
usage: trepl.py main entry_point [arg1 [arg2 ...]]

positional arguments:
  entry_point  The fully-qualified function name followed by any arguments,
               e.g. `trepl.py main foo.core/bar hello 7`. All arguments will
               be passed as strings.

optional arguments:
  -h, --help   show this help message and exit

The trident.cli namespace must be available. This namespace is used to 1) run
the function in the current directory, 2) disable calls to `System/exit` and
`shutdown-agents`. NOTE: the working directory will be changed for the whole
repl process while this command runs. If that's a problem, you may want to run
a dedicated repl for use with this command.

trepl is inspired by Grenchman, but:

• trepl is a single Python file, so it's easier (for me, at least) to develop and install.
• trepl's main command has a couple extra features (see the help output above).
• trepl has much fewer features (only what I need).

Example usage

Start a build repl:

# might want to put this in a file
clj -Sdeps '{:deps {trident/build {:mvn/version "RELEASE"} ; includes trident.cli
                    trident/repl  {:mvn/version "RELEASE"}}}' \
    -e "(do (require 'trident.repl) (trident.repl/init))" -r

(trident.repl/init will start an nRepl server on port 7888 by default.)

Run a build task:

# Requires Python 3
alias build='/path/to/trepl.py -p 7888 main trident.build/-main'
build --help # nice and speedy!