Warn when hooks or implicit middleware is found.

Fixes #2387.

NEWS.md

@@ -1,5 +1,9 @@
 # Leiningen News -- history of user-visible changes
 
+## ??? / ???
+
+* Add project coordinate data to jar metadata. (Conor McDermottroe)
+
 ## 2.8.1 / 2017-10-27
 
 * Fix a bug where `lein help` couldn't list built-in tasks on Java 9. (Phil Hagelberg)

doc/FAQ.md

@@ -252,10 +252,10 @@ bug with the dependency which does this.
 **A:** You probably downloaded `lein`/`lein.bat` from the [master branch](https://github.com/technomancy/leiningen/tree/master/bin). Unless you plan to build leiningen yourself or help develop it, we suggest you use the latest stable version: [lein](https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein)/[lein.bat](https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein.bat)
 
 **Q:** I have a dependency whose group ID and/or artifact ID starts with a
-  number (which is invalid for symbols in Clojure). How can I add it to my
+number (which is invalid for symbols in Clojure). How can I add it to my
-  project's dependencies?  
+project's dependencies?  
 **A:** As of version 2.8.0, Leiningen supports string dependency names like
-  this:
+this:
 
 ```clj
 :dependencies [["net.3scale/3scale-api" "3.0.2"]]
@@ -266,3 +266,15 @@ Prior to version 2.8.0, this is the workaround:
 ```clj
 :dependencies [[~(symbol "net.3scale" "3scale-api") "3.0.2"]]
 ```
+
+**Q:** I'm getting warnings for implicit hooks or implicit middleware.  
+**A:** Hooks are a deprecated feature where plugins can modify the
+behavior of built-in Leiningen functionality; they result in
+situations which can be very difficult to debug and usually point
+to situations in which the original API is not flexible enough.
+
+Leiningen also has a deprecated feature for implicitly loading
+middleware. Middleware is not deprecated but should now be declared using
+`:middleware` instead of being auto-detected from plugins.
+
+Adding `:implicits false` to `project.clj` will disable all implicit features.

doc/PLUGINS.md

@@ -377,11 +377,6 @@ before manually specified hooks.
 
 ### Project Middleware
 
-**Note**: Leiningen supports project middleware in plugins;
-however this mechanism is extremely error-prone and difficult to
-debug. It should be considered deprecated as of 2.8.0 onward and will
-continue to work until version 3.0 but is strongly advised against.
-
 Project middleware is just a function that is called on a project map
 returning a new project map. Middleware gives a plugin the power to do
 any kind of transformation on the project map. However, problems with
@@ -394,7 +389,7 @@ The following middleware injects additional javac options into the project map,
 but only if there are any java source paths in the project:
 
 ```clj
-(ns lein-inject.plugin
+(ns leiningen.inject
   (:require [leiningen.core.project :as p]))
 
 (def javac-params-profile
@@ -406,12 +401,12 @@ but only if there are any java source paths in the project:
     project))
 ```
 
+Projects use middleware by adding `:middleware` as a vector of var
+names into their `project.clj`:
 
-Like hooks, middleware will be applied automatically for plugins if you put it
+```clj
-in `plugin-name.plugin/middleware`. You can also load middleware manually by
+  :middleware [leiningen.inject/middleware]
-setting the `:middleware` key in project.clj to a seq of vars to call to
+```
-transform your project map. Note that automatic middleware is applied before
-manually specified middleware.
 
 Also note that the currently active middleware depends on which
 profiles are active. This means we need to reapply the middleware
@@ -429,6 +424,12 @@ middleware to inject values into the project map is if the profiles has to be
 programmatically computed, or if you have to modify the project map in a way
 that is not possible with `merge-profiles`.
 
+**Note**: Leiningen supports loading middleware implicitly when the
+middleware is named `plugin-name.plugin/middleware`; however this
+mechanism is even more difficult to debug than regular middleware. It
+should be considered deprecated as of 2.8.0 onward and will continue
+to work until version 3.0 but is strongly advised against.
+
 ### Maven Wagons
 
 [Pomegranate](https://github.com/cemerick/pomegranate) (the library

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

@@ -29,7 +29,9 @@
 (defn- warn [& args]
   ;; TODO: remove with 3.0.0
   (require 'leiningen.core.main)
-  ((resolve 'leiningen.core.main/warn) args))
+  (apply (resolve 'leiningen.core.main/warn) args))
+
+(def ^:private warn-once (memoize warn))
 
 (defn- update-each-contained [m keys f & args]
   (reduce (fn [m k]
@@ -389,7 +391,7 @@
              (meta project))))
   ([project]
      (let [repos (if (:omit-default-repositories project)
-                   (do (warn "WARNING:"
+                   (do (warn-once "WARNING:"
                                   ":omit-default-repositories is deprecated;"
                                   "use :repositories ^:replace [...] instead.")
                        empty-repositories)
@@ -675,18 +677,14 @@
                               profiles)]
     (when (and (seq repo-profiles)
                (not (System/getenv "LEIN_SUPPRESS_USER_LEVEL_REPO_WARNINGS")))
-      (warn ":repositories detected in user-level profiles!"
+      (warn-once ":repositories detected in user-level profiles!"
                  (vec (map first repo-profiles)) "\nSee"
                  "https://github.com/technomancy/leiningen/wiki/Repeatability"))))
 
-(alter-var-root #'warn-user-repos memoize)
-
 (defn- warn-user-profile [root profiles]
   (when (and root (contains? profiles :user))
     (warn "WARNING: user-level profile defined in project files.")))
 
-(alter-var-root #'warn-user-profile memoize)
-
 (defn- system-profiles []
   (let [sys-profile-dir (if (= :windows (utils/get-os))
                           (io/file (System/getenv "AllUsersProfile") "Leiningen")
@@ -772,11 +770,14 @@
 
 (defn- load-hook [hook-name]
   (if-let [hook (try (utils/require-resolve hook-name)
-                     (catch Throwable e
+                     (catch Exception e
                        (utils/error "problem requiring" hook-name "hook")
                        (throw e)))]
-    (try (hook)
+    (try (warn-once "Warning: implicit hook found:" hook-name
-         (catch Throwable e
+                    "\nHooks are deprecated and will be removed"
+                    "in a future version.")
+         (hook)
+         (catch Exception e
            (utils/error "problem activating" hook-name "hook")
            (throw e)))
     (when-not (:optional (meta hook-name))
@@ -799,7 +800,11 @@
   ([project middleware-name]
      (if (and (:implicits project true) (:implicit-middleware project true))
        (if-let [middleware (utils/require-resolve middleware-name)]
-         (middleware project)
+         (do (when-not (some #{middleware-name} (:middleware project))
+               (warn-once "Warning: implicit middleware found:" middleware-name
+                          "\nPlease declare all middleware in :middleware"
+                          "as implicit loading is deprecated."))
+             (middleware project))
          (do (when-not (:optional (meta middleware-name))
                (utils/error "cannot resolve" middleware-name "middleware"))
              project))