Skip fetching deps unnecessarily when :checksum-deps is set.

NEWS

@@ -2,6 +2,9 @@ Leiningen NEWS -- history of user-visible changes
 
 = 1.5.0 / ???
 
+* Skip fetching dependencies when they haven't changed in project.clj
+  if :checksum-deps is set.
+
 * Add system property for $PROJECT.version.
 
 * Add deploy task.

sample.project.clj

@@ -36,6 +36,13 @@
                                               javax.jms/jms
                                               com.sun.jdmk/jmxtools
                                               com.sun.jmx/jmxri]]]
+  ;; Dev dependencies are intended for use only during
+  ;; development. Projects that depend on this project will not pull
+  ;; in its dev-dependencies, and they won't be included in the uberjar.
+  :dev-dependencies [[org.clojure/swank-clojure "1.2.1"]]
+  ;; Only re-fetch dependencies when they change in project.clj or
+  ;; when :library-path directory is empty.
+  :checksum-deps true
   ;; Warns users of earlier versions of Leiningen.
   :min-lein-version "1.3.0"
   ;; Before fetching dependencies, the contents of the lib/ directory
@@ -58,10 +65,6 @@
   ;; namespaces matching leiningen.hooks.*. Warning: this will cause
   ;; Leiningen to start slowly, especially with many dependencies.
   :implicit-hooks false
-  ;; Dev dependencies are intended for use only during
-  ;; development. Projects that depend on this project will not pull
-  ;; in its dev-dependencies, and they won't be included in the uberjar.
-  :dev-dependencies [[org.clojure/swank-clojure "1.2.1"]]
   ;; These namespaces will be AOT-compiled. Needed for gen-class and
   ;; other Java interop functionality. :namespaces is an alias for this.
   ;; Put a regex here to compile all namespaces whose names match.

src/leiningen/deps.clj

@@ -5,6 +5,7 @@
         [leiningen.util.maven :only [make-dependency]]
         [leiningen.util.file :only [delete-file-recursively]])
   (:import (java.io File)
+           (java.security MessageDigest)
            (org.apache.maven.artifact.ant Authentication DependenciesTask
                                           RemoteRepository)
            (org.apache.maven.settings Server)
@@ -68,15 +69,30 @@
 (defn use-dev-deps? [project skip-dev]
   (and (not skip-dev) (seq (:dev-dependencies project))))
 
+(defn- sha1-digest [content]
+  (.toString (BigInteger. 1 (-> (MessageDigest/getInstance "SHA1")
+                                (.digest (.getBytes content)))) 16))
+
+(defn- deps-checksum [project]
+  (sha1-digest (pr-str [(:dependencies project)
+                              (:dev-dependencies project)])))
+
+(defn fetch-deps? [project deps-set skip-dev]
+  (let [deps-checksum-file (File. (:root project) ".lein-deps-sum")]
+    (and (or (seq (project deps-set)) (use-dev-deps? project skip-dev))
+         (or (not (:checksum-deps project))
+             (empty? (.list (File. (:library-path project))))
+             (not (.exists deps-checksum-file))
+             (not= (slurp deps-checksum-file) (deps-checksum project))))))
+
 (defn ^{:help-arglists '([] [skip-dev])} deps
   "Download and install all :dependencies and :dev-dependencies listed in
 project.clj. With an argument it will skip development dependencies."
   ([project skip-dev deps-set]
-     (when (or (seq (project deps-set)) (use-dev-deps? project skip-dev))
+     (when (fetch-deps? project deps-set skip-dev)
        (when-not (:disable-implicit-clean project)
-         (delete-file-recursively (:library-path project) true))
-       (let [deps-task (make-deps-task project deps-set)
-             _ (.execute deps-task)
+         (delete-file-recursively (:library-path project) :silently))
+       (let [deps-task (doto (make-deps-task project deps-set) .execute)
              fileset (.getReference lancet/ant-project
                                     (.getFilesetId deps-task))]
          (.mkdirs (File. (:library-path project)))

todo.org

@@ -41,7 +41,6 @@ See also https://github.com/technomancy/leiningen/issues
 ** TODO re-compile all deps with current clojure version
    Another thing that's going to start becoming more important as more
    Clojure versions are introduced.
-** TODO fail gracefully when run without an Internet connection (Issue #100)
 ** TODO improve test coverage
 ** TODO merge push task based on clj-ssh
    lein-clojars task doesn't support DSA keys