[elpa] externals/fontaine 96cece3857: Make it possible to inherit a preset in another preset

[ELPA Syncer]

branch: externals/fontaine
commit 96cece385783a9f19d3a418a8f2150ca8b5c0a58
Author: Protesilaos Stavrou <info@protesilaos.com>
Commit: Protesilaos Stavrou <info@protesilaos.com>

    Make it possible to inherit a preset in another preset
---
 README.org  | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 fontaine.el | 51 +++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 98 insertions(+), 4 deletions(-)

diff --git a/README.org b/README.org
index 3a40b7f445..195f52c152 100644
--- a/README.org
+++ b/README.org
@@ -407,6 +407,57 @@ intend to change their values).  We then have this 
transformation:
          :variable-pitch-height 1.05)))
 #+end_src
 
+** Inherit the properties of another named preset
+:PROPERTIES:
+:CUSTOM_ID: h:9604c817-9b01-46d6-9455-58b8c393e441
+:END:
+
+[ Part of {{{development-version}}}. ]
+
+When defining multiple presets, we may need to duplicate properties
+and then make tweaks to individual values.  Suppose we want to have
+two distinct presets for presentations: one is for coding related
+demonstrations and the other for prose.  Both must have some common
+styles, but must define distinct font families each of which is
+suitable for the given task.  In this case, we do not want to fall
+back to the generic =t= preset and we also do not wish to duplicate
+properties manually, potentially making mistakes in the process.
+Fontaine thus provides a method of inheriting a named preset's
+properties.  Here is the idea:
+
+#+begin_src emacs-lisp
+(setq fontaine-presets
+      '((regular
+         :default-height 100)
+        (code-demo
+         :default-family "Source Code Pro"
+         :default-weight semilight
+         :default-height 170
+         :variable-pitch-family "Sans"
+         :bold-weight extrabold)
+        (prose-demo
+         :inherit code-demo ; copy the `code-demo' properties
+         :default-family "Sans"
+         :variable-pitch-family "Serif"
+         :default-height 220)
+        (t
+         :default-family "Monospace"
+         ;; more generic fallback properties here...
+         )))
+#+end_src
+
+In this scenario, the =regular= preset gets all its properties from
+the =t= preset.  We omit them here in the interest of brevity (see the
+default value of ~fontaine-presets~ and its documentation for the
+details).  In turn, the =code-demo= specifies more properites and
+falls back to =t= for any property not explicitly referenced.
+Finally, the =prose-demo= copies everything in =code-demo=, overrides
+any property therein, and falls back to =t= for every other property.
+
+In the interest of simplicity, Fontaine does not support recursive
+inheritance.  If there is a compelling need for it, we can add it in
+future versions.
+
 * Installation
 :PROPERTIES:
 :CUSTOM_ID: h:031b9bea-d42b-4be0-82c7-42712cde94cc
diff --git a/fontaine.el b/fontaine.el
index fdbd984f39..100b8544b2 100644
--- a/fontaine.el
+++ b/fontaine.el
@@ -225,6 +225,18 @@ The properties in detail:
 - The `:line-spacing' specifies the value of the `line-spacing'
   variable.
 
+- The `:inherit' contains the name of another named preset.  This
+  tells the relevant Fontaine functions to get the properties of
+  that preset and blend them with those of the current one.  The
+  properties of the current preset take precedence over those of
+  the inherited one, thus overriding them.  In practice, this is
+  a way to have something like an extra-large preset copy the
+  large preset and then only modify its individual properties.
+  Remember that all named presets fall back to the preset whose
+  name is t: the `:inherit' is not a substitute for that generic
+  fallback but rather an extra method of specifying font
+  configuration presets.
+
 Use the desired preset with the command `fontaine-set-preset'.
 
 For detailed configuration: Info node `(fontaine) Shared and
@@ -281,12 +293,25 @@ Caveats or further notes:
                     (const reverse-italic)
                     (const reverse-oblique)))
 
-                  ((const :tag "Line spacing" :line-spacing) ,(get 
'line-spacing 'custom-type))))
+                  ((const :tag "Line spacing" :line-spacing) ,(get 
'line-spacing 'custom-type))
+                  ;; FIXME 2023-01-19: Adding the (choice
+                  ;; ,@(fontaine--inheritable-presets-widget)) instead
+                  ;; of `symbol' does not have the desired effect
+                  ;; because it does not re-read `fontaine-presets'.
+                  ((const :tag "Inherit another preset" :inherit) symbol)))
           :key-type symbol)
-  :package-version '(fontaine . "0.4.0")
+  :package-version '(fontaine . "0.5.0")
   :group 'fontaine
   :link '(info-link "(fontaine) Shared and implicit fallback values for 
presets"))
 
+;; ;; See FIXME above in `fontaine-presets' :type.
+;; ;;
+;; (defun fontaine--inheritable-presets-widget ()
+;;   "Return widget with choice among named presets."
+;;   (mapcar (lambda (s)
+;;             (list 'const s))
+;;           (delq t (mapcar #'car fontaine-presets))))
+
 (defcustom fontaine-latest-state-file
   (locate-user-emacs-file "fontaine-latest-state.eld")
   "File to save the latest value of `fontaine-set-preset'.
@@ -374,14 +399,32 @@ combine the other two lists."
 
 ;;;; Apply preset configurations
 
+(defun fontaine--preset-p (preset)
+  "Return non-nil if PRESET is one of the named `fontaine-presets'."
+  (let ((presets (delq t (mapcar #'car fontaine-presets))))
+    (memq preset presets)))
+
+(defun fontaine--get-inherit-name (preset)
+  "Get the `:inherit' value of PRESET."
+  (when-let* ((inherit (plist-get (alist-get preset fontaine-presets) 
:inherit))
+              (fontaine--preset-p inherit))
+    inherit))
+
+(defun fontaine--get-preset-properties (preset)
+  "Return list of properties for PRESET in `fontaine-presets'."
+  (let ((presets fontaine-presets))
+    (append (alist-get preset presets)
+            (when-let ((inherit (fontaine--get-inherit-name preset)))
+              (alist-get inherit presets))
+            (alist-get t presets))))
+
 (defmacro fontaine--apply-preset (fn doc args)
   "Produce function to apply preset.
 FN is the symbol of the function, DOC is its documentation, and
 ARGS are its routines."
   `(defun ,fn (preset &optional frame)
      ,doc
-     (if-let ((properties (append (alist-get preset fontaine-presets)
-                                  (alist-get t fontaine-presets))))
+     (if-let ((properties (fontaine--get-preset-properties preset)))
          ,args
        ;; FIXME 2022-09-07: Because we `append' the t of
        ;; `fontaine-presets' this error is only relevant when the list