Mitigate el-patch-pre-validate-hook boilerplate

See #10.

CHANGELOG.md

@@ -11,6 +11,13 @@ The format is based on [Keep a Changelog].
   linting, and table-of-contents updating.
 * `el-patch` now checks for byte-compilation and checkdoc warnings on
   Travis CI ([#7](https://github.com/raxod502/el-patch/issues/7)).
+* New macro `el-patch-feature` (unrelated to the old obsolete
+  `el-patch-feature` macro that was removed) which is a convenient way
+  to add feature-requiring functions to `el-patch-pre-validate-hook`
+  ([#10](https://github.com/raxod502/el-patch/issues/10)).
+* New user option `el-patch-require-function` for advanced users only.
+  It allows you to integrate `el-patch-feature` with your package
+  manager, and other things like that.
 
 ### Removed
 * Deprecated patch directive `el-patch-feature` has been removed.

README.md

@@ -429,6 +429,12 @@ even enable a custom minor mode). This hook is run before
 `el-patch-validate-all`, and also before `el-patch-validate` when you
 provide a prefix argument.
 
+Since defining some patches after a feature is loaded is such a common
+operation, `el-patch` provides a convenience macro for it:
+`el-patch-feature`. You can call this macro with an (unquoted) feature
+name, and it will create a function that loads that feature, and add
+it to `el-patch-pre-validate-hook` for you.
+
 If you don't want all of your patches to be defined all the time, you
 can put some functions in `el-patch-post-validate-hook` to disable
 them again. For some examples of how to use these hooks, check out

el-patch.el

@@ -67,6 +67,16 @@ before evaluating the new one."
   :type 'boolean
   :group 'el-patch)
 
+(defcustom el-patch-require-function #'require
+  "Function to `require' a feature in `el-patch-pre-validate-hook'.
+This is passed all of the arguments of `el-patch-feature' as
+quoted literals, and it should load the feature. This function
+might be useful if, for example, some of your features are
+provided by lazy-installed packages, and those packages need to
+be installed before the features can be loaded."
+  :type 'function
+  :group 'el-patch)
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;; Internal variables
 
@@ -525,6 +535,26 @@ etc., which may contain patch directives."
            (indent defun))
   `(el-patch--definition ',(cons #'define-minor-mode args)))
 
+;; For convenience.
+
+;;;###autoload
+(defmacro el-patch-feature (feature &rest args)
+  "Declare that some patches are only defined after FEATURE is loaded.
+This is a convenience macro that creates a function for invoking
+`require' on that feature, and then adds it to
+`el-patch-pre-validate-hook' so that your patches are loaded and
+`el-patch' can properly validate them.
+
+FEATURE should be an unquoted symbol. ARGS, if given, are passed
+as quoted literals along with FEATURE to
+`el-patch-require-function' when `el-patch-validate-all' is
+called."
+  (let ((defun-name (intern (format "el-patch-require-%S" feature))))
+    `(progn
+       (defun ,defun-name ()
+         (apply el-patch-require-function ',feature ',args))
+       (add-hook 'el-patch-pre-validate-hook #',defun-name))))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;; Patch directives