From d835d8bf8c1fa2158aa34fd4d99e9fdd3449c593 Mon Sep 17 00:00:00 2001
From: Alexander Sulfrian <alexander.sulfrian@fu-berlin.de>
Date: Mon, 12 Sep 2016 19:59:26 +0200
Subject: use-package: Add :if-installed keyword

With the :if-installed keyword it is possible to check, if a package is
installed before binding keys or creating autoloads. This helps of
optional packages that overwrites built-in keys (like helm with M-x).
---
 init.d/main.org | 61 ++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 47 insertions(+), 14 deletions(-)

diff --git a/init.d/main.org b/init.d/main.org
index 1ec2e9f..a3efc99 100644
--- a/init.d/main.org
+++ b/init.d/main.org
@@ -54,7 +54,39 @@ requirement for this configuration, so I install it here.
     (unless (package-installed-p 'use-package)
       (package-install 'use-package))
     (setq use-package-verbose t)
-    (require 'use-package))
+    (require 'use-package)
+    <<use-package>>)
+#+end_src
+
+*** :if-installed
+
+I extend the basic set of use-package keywords with a new
+one: =:if-installed t= only enables the bind and auto-load hooks if
+the package is installed (checked with =package-installed-p=). It is
+a shorter way to write =:if (package-installed-p "<pkgname>")=. You
+can give another package name to check as argument instead of =t=.
+
+#+begin_src emacs-lisp  :noweb-ref use-package :tangle no
+  (setq use-package-keywords (cons :if-installed use-package-keywords))
+
+  (defun use-package-normalize/:if-installed (name keyword args)
+    (if (null args)
+        t
+      (use-package-only-one (symbol-name keyword) args
+        (lambda (label arg)
+          (if (symbolp arg)
+              arg
+            (use-package-error
+             (concat ":if-installed wants an optional package name "
+                     "(an unquoted symbol name)")))))))
+
+  (defun use-package-handler/:if-installed (name keyword ensure rest state)
+    (let ((body (use-package-process-keywords name rest state))
+          (package-name (or (and (eq ensure t) (use-package-as-symbol name)) ensure)))
+      `((if (package-installed-p ',package-name)
+            (progn ,@body)
+          ,(when (bound-and-true-p use-package-verbose)
+             `(message ,(format "Configuring package %s...SKIPPED" package-name)))))))
 #+end_src
 
 ** auto-compile
@@ -1185,8 +1217,8 @@ the window. It is not optimal, because it does not display the
 possibility. Maybe I will replace it with a custom hydra.
 
 #+begin_src emacs-lisp
-(when (locate-library "ace-window")
   (use-package ace-window
+    :if-installed t
     :bind (("C-x o" . ace-window)
            ("C-x C-o" . aw-flip-window))
     :config
@@ -1198,7 +1230,7 @@ possibility. Maybe I will replace it with a custom hydra.
                               (?v aw-split-window-vert " Ace - Split Vert Window")
                               (?h aw-split-window-horz " Ace - Split Horz Window")
                               (?i delete-other-windows " Ace - Maximize Window")
-                              (?o delete-other-windows)))))
+                              (?o delete-other-windows))))
 #+end_src
 
 ** auto-complete
@@ -1209,18 +1241,19 @@ when pressing the shortcut (but the auto-complete-mode has to be
 enabled before).
 
 #+begin_src emacs-lisp
-  (use-package auto-complete
-    :bind ("M-<tab>" . auto-complete)
-    :demand t
-    :diminish auto-complete-mode
-    :config
-    (require 'auto-complete-config)
-    (ac-config-default)
+    (use-package auto-complete
+      :if-installed t
+      :bind ("M-<tab>" . auto-complete)
+      :demand t
+      :diminish auto-complete-mode
+      :config
+      (require 'auto-complete-config)
+      (ac-config-default)
 
-    (setq ac-comphist-file (alex/cache-file "ac-comphist.dat")
-          ac-quick-help-delay 1.0)
+      (setq ac-comphist-file (alex/cache-file "ac-comphist.dat")
+            ac-quick-help-delay 1.0)
 
-    (global-auto-complete-mode t))
+      (global-auto-complete-mode t))
 #+end_src
 
 ** TODO company-mode
@@ -1410,6 +1443,7 @@ every time I start emacs.
 
 #+begin_src emacs-lisp
   (use-package helm
+    :if-installed t
     :bind (("M-x" . helm-M-x)
            ("M-X" . execute-extended-command)
            ("C-x f" . helm-mini)
@@ -1417,7 +1451,6 @@ every time I start emacs.
            ("C-x C-b" . helm-buffers-list)
            ("M-y" . helm-show-kill-ring))
     :demand t
-    :ensure t
     :diminish helm-mode
     :config
     <<helm-config>>
-- 
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