Slamhound

They sent a slamhound on Turner's trail in New Delhi, slotted it
to his pheromones and the color of his hair. It caught up with him
on a street called Chandni Chauk and came scrambling for his
rented BMW through a forest of bare brown legs and pedicab
tires. Its core was a kilogram of recrystallized hexogene and
flaked TNT. He didn't see it coming. The last he saw of India was
the pink stucco facade of a place called the Khush-Oil Hotel.

Because he had a good agent, he had a good contract. Because he
had a good contract, he was in Singapore an hour after the
explosion. Most of him, anyway. The Dutch surgeon liked to joke
about that, how an unspecified percentage of Turner hadn't made it
out of Palam International on that first flight and had to spend
the night there in a shed, in a support vat.

It took the Dutchman and his team three months to put Turner
together again. They cloned a square meter of skin for him, grew
it on slabs of collagen and shark-cartilage polysaccharides. They
bought eyes and genitals on the open market. The eyes were green.

-- Count Zero, page 1. By William Gibson

Slamhound rips your ns form apart and reconstructs it. No Dutch surgeon required.

Add [slamhound "1.5.5"] to the :dependencies of your :user profile.

This project is no longer under active development.

Screencast

http://vimeo.com/80650659

Leiningen Usage

Make an alias for run -m slam.hound in your :user profile:

  :aliases {"slamhound" ["run" "-m" "slam.hound"]}

Take a namespace with a sparse ns form that won't compile:

$ cat src/my/namespace.clj # before: ns form is missing clauses

(ns my.namespace
  "I have a doc string.")

(defn -main [& args]
  (pprint args)
  (io/copy (ByteArrayInputStream. (.getBytes "hello"))
           (first args)))

Then run slamhound on it:

$ lein slamhound src/my/namespace.clj # [... thinking ...]

$ cat src/my/namespace.clj  # after: spits out new ns form
(ns my.namespace
  "I have a doc string."
  (:require [clojure.java.io :as io]
            [clojure.pprint :refer [pprint]])
  (:import (java.io ByteArrayInputStream)))

Like magic.

Running on a directory will perform the same operation on every .clj file inside.

Repl Usage

You can reconstruct namespaces from a repl to avoid the slow startup time:

user=> (require '[slam.hound :refer [reconstruct]])
nil
user=> (println (reconstruct "src/my/namespace.clj"))
(ns my.namespace
  "I have a doc string."
  (:require [clojure.java.io :as io]
            [clojure.pprint :refer [pprint]])
  (:import (java.io ByteArrayInputStream)))

Or to reconstruct files in place:

user=> (slam.hound/swap-in-reconstructed-ns-form "src/my/namespace.clj")
nil
;; Reload the file in your editor to pick up changes

Emacs Usage

The included slamhound.el allows for convenient access within nREPL or SLIME sessions via M-x slamhound. Install manually or via Marmalade.

Vim Usage

Install vim-slamhound for use of the :Slamhound command within Clojure buffers.

Light Table Usage

Install slamhound-lt from the central plugin repository.

Shortcomings

Syntax-quoted references

Slamhound will only find references in a namespace that are consumed within the namespace itself. For example, if you have a macro that refers to a var inside syntax-quote (backtick), but the macro is only called from other namespaces, then Slamhound won't detect the reference and will instead report the failure in the namespace in which the macro is called.

You can work around this problem by attaching dummy metadata to the defmacro form to prevent it from compiling without the necessary references being present:

(defmacro defexample
  "Metadata can be attached to a macro by specifying an `attr-map`
  between the docstring and the params vector."
  {:requires [AClass a-var an/aliased-var #'a-macro]}
  [name & args]
  `(do (def ~(str name \*) (AClass. ~@args))
       (def ~(str name \-) (a-var ~@args))
       (def ~(str name \+) (an/aliased-var ~@args))
       (def ~(str name \!) (a-macro ~@args))))

Notice that macros must be referenced with #' to avoid a Can't take the value of a macro error.

If the syntax quoted references refer to functions, classes, or constant data, unquoting them will work as well:

(defmacro defexample
  {:requires [#'a-macro]}
  [name & args]
  `(do (def ~(str name \*) (new ~AClass ~@args))
       (def ~(str name \-) (~a-var ~@args))
       (def ~(str name \+) (~an/aliased-var ~@args))
       (def ~(str name \!) (a-macro ~@args))))

In this case Aclass, a-var, and an/aliased-var must be resolved at compile time, so Slamhound will successfully find these references.

Note that the shorter reader macro form (AClass. ~@args) must be expanded to (new ~AClass ~@args) and that macros cannot be unquoted.

Fully qualified and dynamically resolved Vars

Slamhound will also not find references to fully-qualified vars or vars resolved at runtime since it relies on detecting compilation failures to determine when it's done.

PermGen memory pressure

Slamhound aggressively creates and destroys namespaces during reconstruction. This taxes the class loading system, so there is a possibility that the JVM may run out of PermGen space in large projects. If this happens, try running your JVM with the following option to enable garbage collection of discarded classes:

-XX:+CMSClassUnloadingEnabled

Side effects during namespace evaluation

As namespaces may potentially be reloaded many times during reconstruction, it is important that no side-effects (aside from var definition) occur during namespace evaluation.

Leiningen 1.x

The lein-slamhound plugin is deprecated, and the :aliases approach above is recommended for users of Leiningen 2. However, if you are still using Leiningen 1.x you can use the run task:

$ lein run -m slam.hound src/foo

Since Leiningen 1.x doesn't support partially-applied aliases, you would have to make a shell alias if you don't want to type the full invocation out every time.

License

Copyright © 2011-2012 Phil Hagelberg and contributors

Distributed under the Eclipse Public License, the same as Clojure.