support disabling autoload of plugin hooks and middleware

doc/PLUGINS.md

@@ -209,6 +209,20 @@ map whenever the active profiles change. We accomplish this by storing the fresh
 project map and starting from that whenever we call `merge-profiles`,
 `unmerge-profiles` or `set-profiles`.
 
+## Requiring Plugins
+
+To use a plugin in your project, just add a `:plugins` key to your project.clj
+with the same format as `:dependencies`. In addition to the options allowed by
+`:dependencies`, `:plugins` also allows you to disable auto-loading of hooks or
+middleware.
+
+```clj
+(defproject foo "0.1.0"
+  :plugins [[lein-pprint "1.1.1"]
+            [lein-foo "0.0.1" :hooks false]
+            [lein-bar "0.0.1" :middleware false]])
+```
+
 ## Clojure Version
 
 Leiningen 2.0.0 uses Clojure 1.4.0. If you need to use a different

leiningen-core/src/leiningen/core/project.clj

@@ -264,10 +264,11 @@
      project)
   ([project] (load-plugins project :plugins)))
 
-(defn- plugin-vars [project var-name]
-  (for [[plugin] (:plugins project)]
+(defn plugin-vars [project type]
+  (for [[plugin _ & {:as opts}] (:plugins project)
+        :when (get opts type true)]
     (with-meta (symbol (str (name plugin) ".plugin")
-                       (name var-name))
+                       (name type))
       {:optional true})))
 
 (defn- plugin-hooks [project]

leiningen-core/test/leiningen/core/test/project.clj

@@ -127,6 +127,21 @@
            (binding [*err* *out*]
              (init-project (read (.getFile (io/resource "p3.clj")))))))))
 
+(deftest test-plugin-vars
+  (are [project hooks middleware] (= (list hooks middleware)
+                                     (map (partial plugin-vars project) [:hooks :middleware]))
+       {:plugins '[[lein-foo "1.2.3"]]}
+       '(lein-foo.plugin/hooks) '(lein-foo.plugin/middleware)
+
+       {:plugins '[[lein-foo "1.2.3" :hooks false]]}
+       '() '(lein-foo.plugin/middleware)
+
+       {:plugins '[[lein-foo "1.2.3" :middleware false]]}
+       '(lein-foo.plugin/hooks) '()
+
+       {:plugins '[[lein-foo "1.2.3" :hooks false :middleware false]]}
+       '() '()))
+
 (deftest test-add-profiles
   (let [expected-result {:dependencies [] :profiles {:a1 {:src-paths ["a1/"]}
                                                      :a2 {:src-paths ["a2/"]}}}]

sample.project.clj

@@ -47,7 +47,9 @@
   ;; provides new tasks or hooks.
   :plugins [[lein-pprint "1.1.1"]
             [lein-assoc "0.1.0"]
-            [s3-wagon-private "1.1.1"]]
+            [s3-wagon-private "1.1.1"]
+            [lein-foo "0.0.1" :hooks false]
+            [lein-bar "0.0.1" :middleware false]]
   ;; If you configure a custom repository with a self-signed SSL
   ;; certificate, you will need to add it here. Paths should be either
   ;; be on Leiningen's classpath or relative to the project root.