Lint your Clojure programs as they run
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README.md

ABANDONED

The original author has abandoned this approach. Please fork if you want to continue this work, otherwise please do not send new PR's.

Dynalint

Lint your Clojure programs as they run.

Dynalint is a simplistic linter that wraps operations in runtime checks. It is designed to never change behaviour, except for throwing different kinds of exceptions for bad input.

Preserving performance is not a goal of Dynalint, but it will always preserve type hints.

Designed for Clojure 1.5.1, but has been modified so it can be tried with Clojure 1.6.0, too.

Caveat: Prone to blowing the stack

Dynalint's design is intrinsically prone to cyclic calling. If you get a StackOverflowException where a Dynalint namespace is obviously to blame, please stop using Dynalint for your project and file an issue.

Usage

Dynalint should only be used at dev time. You can start it manually in a REPL, or in a Leiningen project you may modify your project.clj file to start it automatically for you.

No matter how you start Dynalint, it is enabled by calling its lint function. lint adds dynamic checks to vars and their inlinings.

If you want to check a var's inlining or a macro's expansion, relevant forms must be compiled after calling lint.

Starting Dynalint manually

Add this to your project's dependencies:

[com.ambrosebs/dynalint "0.1.3"]

If you want to use Dynalint at the REPL, call dynalint.lint/lint.

(require '[dynalint.lint :as dyn])
(dyn/lint)

Starting Dynalint automatically with Leiningen

If you want Dynalint to be automatically enabled every time you run lein test or lein repl, here is a minimal project.clj file example that can achieve that:

(defproject testdyna "0.1.0"
  ;; ... other stuff here ...
  :profiles {:dev {:dependencies [[com.ambrosebs/dynalint "0.1.3"]]
                   :injections [(require 'dynalint.lint)
                                (dynalint.lint/lint)]}}
  ;; ... other stuff here ...
  )

If you move the :injections keyword and its value to a :test profile, Dynalint will be enabled near the beginning of lein test, but not lein repl.

Dynalint options

Change (dynalint.lint/lint) to (dynalint.lint/lint :start-message true) if you want to enable a 1-line startup message to be printed to *out* when dynalint.lint/lint is called, to verify that it is being called in your project.

Other options that can be supplied to lint:

  • :log-file "filename" - Dynalint will create the directory containing filename, delete the file, and then write to it the full stack trace of every lint warning or error generated.
  • :warning-interval 0.1 - Specify the minimum time in seconds that Dynalint will issue consecutive warnings. Specifying 0 or nil will show all warnings. The default is 1 second. If this value is neither 0 nor nil, the warnings printed by Dynalint can change from one run to the next, due to variations in execution time.
  • :enable - The value can be a single keyword :all, :error, or :warn, or a sequence of those keywords. By default, both :error and :warn are enabled.
  • :disable - The values are the same as for :enable above.

The following example enables the start message and logging to file dynalint-log.txt. It disables the minimum time interval between warnings, thus showing all of them, no matter how close in time they occur.

(defproject testdyna "0.1.0"
  ;; ... other stuff here ...
  :profiles {:dev {:dependencies [[com.ambrosebs/dynalint "0.1.4-SNAPSHOT"]]
                   :injections [(require 'dynalint.lint)
                                (dynalint.lint/lint
                                  :start-message true
                                  :log-file "dynalint-log.txt"
                                  :warning-interval nil)]}}
  ;; ... other stuff here ...
  )

Example

Errors

For one reason or another, many core Clojure functions have bad error messages. Here's one example.

user=> (first 1)
IllegalArgumentException Don't know how to create ISeq from: java.lang.Long  clojure.lang.RT.seqFrom (RT.java:505)

user=> (clojure.repl/pst)
IllegalArgumentException Don't know how to create ISeq from: java.lang.Long
  clojure.lang.RT.seqFrom (RT.java:505)
  clojure.lang.RT.seq (RT.java:486)
  clojure.lang.RT.first (RT.java:578)
  clojure.core/first (core.clj:55)
  user/eval52988 (NO_SOURCE_FILE:1)
  clojure.lang.Compiler.eval (Compiler.java:6619)
  clojure.lang.Compiler.eval (Compiler.java:6582)
  clojure.core/eval (core.clj:2852)
  clojure.main/repl/read-eval-print--6588/fn--6591 (main.clj:259)
  clojure.main/repl/read-eval-print--6588 (main.clj:259)
  clojure.main/repl/fn--6597 (main.clj:277)
  clojure.main/repl (main.clj:277)

The error originates from passing bogus arguments to first, yet we get an error deep in first's implementation. This is simply pragmatism as such error checking would incur a performance penalty, but sometimes we just want a better error above all else.

After running (dynalint.lint/lint) we can achieve better errors.

user=> (require '[dynalint.lint :as dyn])
nil
user=> (dyn/lint)
:ok
user=> (first 1)
ExceptionInfo ERROR (Dynalint id 1): First argument to clojure.core/first must be seqable: 1 (instance of class java.lang.Long)  dynalint.lint/error (lint.clj:63)

user=> (clojure.repl/pst)
ExceptionInfo ERROR (Dynalint id 1): First argument to clojure.core/first must be seqable: 1 (instance of class java.lang.Long) {:dynalint.lint/dynalint true, :dynalint.lint/error true, :dynalint.lint/id 1}
  dynalint.lint/error (lint.clj:63)
  clojure.core/first (core.clj:49)
  clojure.lang.AFunction$1.doInvoke (AFunction.java:29)
  user/eval2098 (NO_SOURCE_FILE:1)
  clojure.lang.Compiler.eval (Compiler.java:6619)
  clojure.lang.Compiler.eval (Compiler.java:6582)
  clojure.core/eval (core.clj:2852)
  clojure.main/repl/read-eval-print--6588/fn--6591 (main.clj:259)
  clojure.main/repl/read-eval-print--6588 (main.clj:259)
  clojure.main/repl/fn--6597 (main.clj:277)
  clojure.main/repl (main.clj:277)
  clojure.tools.nrepl.middleware.interruptible-eval/evaluate/fn--660 (interruptible_eval.clj:56)

Dynalint tries to cover it's tracks in the stack trace. Notice it seems dynalint.lint/error is directly called by clojure.core/first. This is not really the case, but the stack trace is transformed to be as understandable as possible.

If you happen to get a stack trace not thrown by dynalint, you will notice calls to strange looking functions like dynalint.lint$clojure.core_SLASH_first$wrapper__8482. This should be interpretted as dynalint's wrapper for clojure.core/first, and for most purposes exactly the same as a stack entry calling clojure.core/first.

Configuring the linter

Use dynalint.lint/configure-linting! to customise your linting experience. Note that dynalint.lint/lint also takes the same arguments, but should only usually be run once.

Rules for Dynalint errors and warnings

The eventual goal is to have Dynalint modifications for all functions and macros in Clojure, even if the only change is to give a different warning for the wrong number of arguments (e.g. clojure.core/meta, clojure.core/number?, and others).

Dynalint should give an error only when the original function/macro would throw an exception, or is known to go into an infinite loop. For all other conditions, Dynalint issues a warning.

Contributions

Clojure CA required please.

License

Copyright © 2014 Ambrose Bonnaire-Sergeant

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