guns/warn-closeable

Warn on potentially unclosed (Auto)Closeable resources.

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|  |  |  |  _  |   _|     |___|  __|  |  _  |__ --|  -__|  _  |  _  |  |  -__|
|________|___._|__| |__|__|   |____|__|_____|_____|_____|___._|_____|__|_____|

A simple linter for Clojure namespaces that detects possibly unclosed instances of (Auto)Closeable objects. A similar feature exists for the Eclipse IDE.

This project will optimally be included as an Eastwood linter.

I am currently waiting for clarification regarding type information from tools.analyzer.jvm, but the core functionality is mostly complete.

Usage

Available as a Leiningen plugin or as a library for use from a REPL.

• Leiningen plugin:

;; ~/.lein/profiles.clj
;; {:user {:plugins [[lein-warn-closeable "0.1.0"]]}}
"NOT AVAILABLE; INSTALL FROM SOURCE"

Run lein warn-closeable from your project root.

• REPL usage

;; ~/.lein/profiles.clj
;; {:user {:dependencies [[com.sungpae/warn-closeable "0.1.0"]]}}
"NOT AVAILABLE; INSTALL FROM SOURCE"

Then:

(require '[com.sungpae.warn-closeable :as wc])

(wc/closeable-warnings *ns*) ; Lint current namespace
(wc/warn-closeable!)         ; Lint all namespaces, same as `lein warn-closeable`

Rationale

The Closeable interface (and the AutoCloseable interface in JRE 1.7+) represents a resource that must be manually closed, like open files and network sockets.

While the .close method of (Auto)Closeable objects are often called in the object finalizer, there is no guarantee that objects will ever be finalized. Therefore, resources must be explicitly closed to avoid resource leaks, which in turn may lead to undesirable exceptions like:

java.io.FileNotFoundException: (Too many open files)

A common convention in JVM languages is to close an (Auto)Closeable object in a finally block after opening the resource:

(let [s (java.net.Socket.)]
  (try
    …
    (finally
      (.close s))))

This is usually written in Clojure with the with-open macro, which expands to the same code as above:

(with-open [s (java.net.Socket.)]
  …)

warn-closeable and lein-warn-closeable, leveraging the power of tools.analyzer, can detect when an (Auto)Closeable object has been created without an associated .close call in a finally block.

MORE DOCUMENTATION HERE