From 810baea2eae5340f4eab56a1a46e13e1d8eeebe7 Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gerry.agbobada-ext@ledger.fr>
Date: Thu, 9 Jan 2020 10:24:41 +0100
Subject: [PATCH 1/7] Use composite to call harfbuzz for ligatures

This is based on code from microsoft -> cascadia-code repository
(issue #153), which sets a
proper composition-function-table according to specific ligature regexp.

Using variables also allows to disable the ligatures for org-mode, where
org-bullets might be incompatible

It has a fallback to old pretty-code behaviour.
---
 modules/ui/pretty-code/config.el | 85 ++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index 6622c8fef..9c9d46300 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -98,10 +98,95 @@ Otherwise it builds `prettify-code-symbols-alist' according to
 
 (add-hook 'after-change-major-mode-hook #'+pretty-code-init-pretty-symbols-h)
 
+(defvar +prog-ligatures-alist
+  '((?! . ".\\(?:\\(==\\|[!=]\\)[!=]?\\)")
+    (?# . ".\\(?:\\(###?\\|_(\\|[(:=?[_{]\\)[#(:=?[_{]?\\)")
+    (?$ . ".\\(?:\\(>\\)>?\\)")
+    (?% . ".\\(?:\\(%\\)%?\\)")
+    (?& . ".\\(?:\\(&\\)&?\\)")
+    (?* . ".\\(?:\\(\\*\\*\\|[*>]\\)[*>]?\\)")
+    ;; (?* . ".\\(?:\\(\\*\\*\\|[*/>]\\).?\\)")
+    (?+ . ".\\(?:\\([>]\\)>?\\)")
+    ;; (?+ . ".\\(?:\\(\\+\\+\\|[+>]\\).?\\)")
+    (?- . ".\\(?:\\(-[->]\\|<<\\|>>\\|[-<>|~]\\)[-<>|~]?\\)")
+    ;; (?. . ".\\(?:\\(\\.[.<]\\|[-.=]\\)[-.<=]?\\)")
+    (?. . ".\\(?:\\(\\.<\\|[-=]\\)[-<=]?\\)")
+    (?/ . ".\\(?:\\(//\\|==\\|[=>]\\)[/=>]?\\)")
+    ;; (?/ . ".\\(?:\\(//\\|==\\|[*/=>]\\).?\\)")
+    (?0 . ".\\(?:\\(x[a-fA-F0-9]\\).?\\)")
+    (?: . ".\\(?:\\(::\\|[:<=>]\\)[:<=>]?\\)")
+    (59 . ".\\(?:\\(;\\);?\\)") ;; 59 is ;
+    (?< . ".\\(?:\\(!--\\|\\$>\\|\\*>\\|\\+>\\|-[-<>|]\\|/>\\|<[-<=]\\|=[<>|]\\|==>?\\||>\\||||?\\|~[>~]\\|[$*+/:<=>|~-]\\)[$*+/:<=>|~-]?\\)")
+    (?= . ".\\(?:\\(!=\\|/=\\|:=\\|<<\\|=[=>]\\|>>\\|[=>]\\)[=<>]?\\)")
+    (?> . ".\\(?:\\(->\\|=>\\|>[-=>]\\|[-:=>]\\)[-:=>]?\\)")
+    (?? . ".\\(?:\\([.:=?]\\)[.:=?]?\\)")
+    (91 . ".\\(?:\\(|\\)[]|]?\\)") ;; 91 is [
+    ;; (?\ . ".\\(?:\\([\\n]\\)[\\]?\\)")
+    (?^ . ".\\(?:\\(=\\)=?\\)")
+    (?_ . ".\\(?:\\(|_\\|[_]\\)_?\\)")
+    (?w . ".\\(?:\\(ww\\)w?\\)")
+    (?{ . ".\\(?:\\(|\\)[|}]?\\)")
+    (?| . ".\\(?:\\(->\\|=>\\||[-=>]\\||||*>\\|[]=>|}-]\\).?\\)")
+    (?~ . ".\\(?:\\(~>\\|[-=>@~]\\)[-=>@~]?\\)"))
+  "An alist containing all the ligatures used when in a `+prog-ligatures-modes' mode.
+
+The car is the character ASCII number, cdr is a regex which will call `font-shape-gstring'
+when matched.
+
+Because of the underlying code in :ui pretty-code module, the regex should match a string
+starting with the character contained in car."
+  )
+
+;; Defaults to not org-mode because org-bullets might be incompatible
+;; with the ?*-based replacements in the default value of +prg-ligatures-alist
+(defvar +prog-ligatures-modes '(not org-mode)
+  "List of major modes in which ligatures should be enabled.
+
+If t, enable it everywhere.
+
+If the first element is 'not, enable it in any mode besides what is listed.
+
+If nil, fallback to the prettify-symbols based replacement (add +font features to pretty-code)."
+  )
+
+(defun +pretty-code-init-ligatures-h ()
+  "Enable ligatures.
+
+If in fundamental-mode, or a mode derived from special, comint, eshell or term
+modes, this function does nothing.
+
+Otherwise it sets the buffer-local composition table to a composition table enhanced with
+`+prog-ligatures-alist' ligatures regexes."
+  (unless (or (eq major-mode 'fundamental-mode)
+              (eq (get major-mode 'mode-class) 'special)
+              (derived-mode-p 'comint-mode 'eshell-mode 'term-mode))
+    (when (or (eq +prog-ligatures-modes t)
+              (if (eq (car +prog-ligatures-modes) 'not)
+                  (not (memq major-mode (cdr +prog-ligatures-modes)))
+                (memq major-mode +prog-ligatures-modes)))
+      (setq-local composition-function-table composition-ligature-table))))
+
+(add-hook 'after-change-major-mode-hook #'+pretty-code-init-ligatures-h)
+
+(use-package! composite
+  :when (and (version<= "27.0" emacs-version) (string-match-p "HARFBUZZ" system-configuration-features))
+  :init
+  (defvar composition-ligature-table (make-char-table nil))
+  :config
+  (dolist (char-regexp +prog-ligatures-alist)
+    (set-char-table-range composition-ligature-table (car char-regexp)
+                          `([,(cdr char-regexp) 0 font-shape-gstring])))
+  (set-char-table-parent composition-ligature-table composition-function-table))
+
 ;; The emacs-mac build of Emacs appear to have built-in support for ligatures,
 ;; so use that instead if this module is enabled.
 (cond ((and IS-MAC (fboundp 'mac-auto-operator-composition-mode))
        (mac-auto-operator-composition-mode))
+      ;; Harfbuzz builds do not need font-specific ligature support
+      ((and (version<= "27.0" emacs-version)
+            (string-match-p "HARFBUZZ" system-configuration-features)
+            (not (null +prog-ligatures-modes)))
+       nil)
       ;; Font-specific ligature support
       ((featurep! +fira)
        (load! "+fira"))

From 03748d48cd54a69dff5a57eba367d1043050abbf Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gerry.agbobada-ext@ledger.fr>
Date: Tue, 14 Apr 2020 20:09:33 +0200
Subject: [PATCH 2/7] Add the explicit character at the beginning of the regexp

---
 modules/ui/pretty-code/config.el | 58 ++++++++++++++++----------------
 1 file changed, 29 insertions(+), 29 deletions(-)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index 9c9d46300..8dd1463cb 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -99,35 +99,35 @@ Otherwise it builds `prettify-code-symbols-alist' according to
 (add-hook 'after-change-major-mode-hook #'+pretty-code-init-pretty-symbols-h)
 
 (defvar +prog-ligatures-alist
-  '((?! . ".\\(?:\\(==\\|[!=]\\)[!=]?\\)")
-    (?# . ".\\(?:\\(###?\\|_(\\|[(:=?[_{]\\)[#(:=?[_{]?\\)")
-    (?$ . ".\\(?:\\(>\\)>?\\)")
-    (?% . ".\\(?:\\(%\\)%?\\)")
-    (?& . ".\\(?:\\(&\\)&?\\)")
-    (?* . ".\\(?:\\(\\*\\*\\|[*>]\\)[*>]?\\)")
-    ;; (?* . ".\\(?:\\(\\*\\*\\|[*/>]\\).?\\)")
-    (?+ . ".\\(?:\\([>]\\)>?\\)")
-    ;; (?+ . ".\\(?:\\(\\+\\+\\|[+>]\\).?\\)")
-    (?- . ".\\(?:\\(-[->]\\|<<\\|>>\\|[-<>|~]\\)[-<>|~]?\\)")
-    ;; (?. . ".\\(?:\\(\\.[.<]\\|[-.=]\\)[-.<=]?\\)")
-    (?. . ".\\(?:\\(\\.<\\|[-=]\\)[-<=]?\\)")
-    (?/ . ".\\(?:\\(//\\|==\\|[=>]\\)[/=>]?\\)")
-    ;; (?/ . ".\\(?:\\(//\\|==\\|[*/=>]\\).?\\)")
-    (?0 . ".\\(?:\\(x[a-fA-F0-9]\\).?\\)")
-    (?: . ".\\(?:\\(::\\|[:<=>]\\)[:<=>]?\\)")
-    (59 . ".\\(?:\\(;\\);?\\)") ;; 59 is ;
-    (?< . ".\\(?:\\(!--\\|\\$>\\|\\*>\\|\\+>\\|-[-<>|]\\|/>\\|<[-<=]\\|=[<>|]\\|==>?\\||>\\||||?\\|~[>~]\\|[$*+/:<=>|~-]\\)[$*+/:<=>|~-]?\\)")
-    (?= . ".\\(?:\\(!=\\|/=\\|:=\\|<<\\|=[=>]\\|>>\\|[=>]\\)[=<>]?\\)")
-    (?> . ".\\(?:\\(->\\|=>\\|>[-=>]\\|[-:=>]\\)[-:=>]?\\)")
-    (?? . ".\\(?:\\([.:=?]\\)[.:=?]?\\)")
-    (91 . ".\\(?:\\(|\\)[]|]?\\)") ;; 91 is [
-    ;; (?\ . ".\\(?:\\([\\n]\\)[\\]?\\)")
-    (?^ . ".\\(?:\\(=\\)=?\\)")
-    (?_ . ".\\(?:\\(|_\\|[_]\\)_?\\)")
-    (?w . ".\\(?:\\(ww\\)w?\\)")
-    (?{ . ".\\(?:\\(|\\)[|}]?\\)")
-    (?| . ".\\(?:\\(->\\|=>\\||[-=>]\\||||*>\\|[]=>|}-]\\).?\\)")
-    (?~ . ".\\(?:\\(~>\\|[-=>@~]\\)[-=>@~]?\\)"))
+  '((?! . "!\\(?:\\(==\\|[!=]\\)[!=]?\\)")
+    (?# . "#\\(?:\\(###?\\|_(\\|[(:=?[_{]\\)[#(:=?[_{]?\\)")
+    (?$ . "$\\(?:\\(>\\)>?\\)")
+    (?% . "%\\(?:\\(%\\)%?\\)")
+    (?& . "&\\(?:\\(&\\)&?\\)")
+    (?* . "*\\(?:\\(\\*\\*\\|[*>]\\)[*>]?\\)")
+    ;; (?* . "*\\(?:\\(\\*\\*\\|[*/>]\\).?\\)")
+    (?+ . "+\\(?:\\([>]\\)>?\\)")
+    ;; (?+ . "+\\(?:\\(\\+\\+\\|[+>]\\).?\\)")
+    (?- . "-\\(?:\\(-[->]\\|<<\\|>>\\|[-<>|~]\\)[-<>|~]?\\)")
+    ;; (?. . "\\.\\(?:\\(\\.[.<]\\|[-.=]\\)[-.<=]?\\)")
+    (?. . "\\.\\(?:\\(\\.<\\|[-=]\\)[-<=]?\\)")
+    (?/ . "/\\(?:\\(//\\|==\\|[=>]\\)[/=>]?\\)")
+    ;; (?/ . "/\\(?:\\(//\\|==\\|[*/=>]\\).?\\)")
+    (?0 . "0\\(?:\\(x[a-fA-F0-9]\\).?\\)")
+    (?: . ":\\(?:\\(::\\|[:<=>]\\)[:<=>]?\\)")
+    (59 . ";\\(?:\\(;\\);?\\)") ;; 59 is ;
+    (?< . "<\\(?:\\(!--\\|\\$>\\|\\*>\\|\\+>\\|-[-<>|]\\|/>\\|<[-<=]\\|=[<>|]\\|==>?\\||>\\||||?\\|~[>~]\\|[$*+/:<=>|~-]\\)[$*+/:<=>|~-]?\\)")
+    (?= . "=\\(?:\\(!=\\|/=\\|:=\\|<<\\|=[=>]\\|>>\\|[=>]\\)[=<>]?\\)")
+    (?> . ">\\(?:\\(->\\|=>\\|>[-=>]\\|[-:=>]\\)[-:=>]?\\)")
+    (?? . "?\\(?:\\([.:=?]\\)[.:=?]?\\)")
+    (91 . "\\[\\(?:\\(|\\)[]|]?\\)") ;; 91 is [
+    ;; (?\ . "\\\\\\(?:\\([\\n]\\)[\\]?\\)")
+    (?^ . "^\\(?:\\(=\\)=?\\)")
+    (?_ . "_\\(?:\\(|_\\|[_]\\)_?\\)")
+    (?w . "w\\(?:\\(ww\\)w?\\)")
+    (?{ . "{\\(?:\\(|\\)[|}]?\\)")
+    (?| . "|\\(?:\\(->\\|=>\\||[-=>]\\||||*>\\|[]=>|}-]\\).?\\)")
+    (?~ . "~\\(?:\\(~>\\|[-=>@~]\\)[-=>@~]?\\)"))
   "An alist containing all the ligatures used when in a `+prog-ligatures-modes' mode.
 
 The car is the character ASCII number, cdr is a regex which will call `font-shape-gstring'

From 9a79069ab5f6d4c2e5781c48ccbbd0f69bb56b0a Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gagbobada+git@gmail.com>
Date: Sat, 25 Apr 2020 16:58:27 +0200
Subject: [PATCH 3/7] Version-gate the feature to emacs 28

---
 modules/ui/pretty-code/config.el | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index 8dd1463cb..cb879d602 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -169,7 +169,8 @@ Otherwise it sets the buffer-local composition table to a composition table enha
 (add-hook 'after-change-major-mode-hook #'+pretty-code-init-ligatures-h)
 
 (use-package! composite
-  :when (and (version<= "27.0" emacs-version) (string-match-p "HARFBUZZ" system-configuration-features))
+  ;; Starting from emacs "28" because this code breaks without fe903c5
+  :when (and (version<= "28.0" emacs-version) (string-match-p "HARFBUZZ" system-configuration-features))
   :init
   (defvar composition-ligature-table (make-char-table nil))
   :config
@@ -183,7 +184,8 @@ Otherwise it sets the buffer-local composition table to a composition table enha
 (cond ((and IS-MAC (fboundp 'mac-auto-operator-composition-mode))
        (mac-auto-operator-composition-mode))
       ;; Harfbuzz builds do not need font-specific ligature support
-      ((and (version<= "27.0" emacs-version)
+      ;; if they brought in the fe903c5 commit
+      ((and (version<= "28.0" emacs-version)
             (string-match-p "HARFBUZZ" system-configuration-features)
             (not (null +prog-ligatures-modes)))
        nil)

From 8a2f8bf2603a4deab06af2921cc583a8f6bb44a8 Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gagbobada+git@gmail.com>
Date: Sat, 25 Apr 2020 17:54:51 +0200
Subject: [PATCH 4/7] Lint code

---
 modules/ui/pretty-code/config.el | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index cb879d602..cf02e7ed1 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -98,6 +98,7 @@ Otherwise it builds `prettify-code-symbols-alist' according to
 
 (add-hook 'after-change-major-mode-hook #'+pretty-code-init-pretty-symbols-h)
 
+;;; Automatic font-specific ligatures
 (defvar +prog-ligatures-alist
   '((?! . "!\\(?:\\(==\\|[!=]\\)[!=]?\\)")
     (?# . "#\\(?:\\(###?\\|_(\\|[(:=?[_{]\\)[#(:=?[_{]?\\)")
@@ -134,20 +135,19 @@ The car is the character ASCII number, cdr is a regex which will call `font-shap
 when matched.
 
 Because of the underlying code in :ui pretty-code module, the regex should match a string
-starting with the character contained in car."
-  )
+starting with the character contained in car.
+
+This variable is used only if you built Emacs with Harfbuzz on a version >= 28")
 
-;; Defaults to not org-mode because org-bullets might be incompatible
-;; with the ?*-based replacements in the default value of +prg-ligatures-alist
 (defvar +prog-ligatures-modes '(not org-mode)
   "List of major modes in which ligatures should be enabled.
 
-If t, enable it everywhere.
+If t, enable it everywhere. Fundamental mode, and modes derived from special-mode,
+comint-mode, eshell-mode and term-mode are *still* excluded.
 
 If the first element is 'not, enable it in any mode besides what is listed.
 
-If nil, fallback to the prettify-symbols based replacement (add +font features to pretty-code)."
-  )
+If nil, fallback to the prettify-symbols based replacement (add +font features to pretty-code).")
 
 (defun +pretty-code-init-ligatures-h ()
   "Enable ligatures.
@@ -184,7 +184,7 @@ Otherwise it sets the buffer-local composition table to a composition table enha
 (cond ((and IS-MAC (fboundp 'mac-auto-operator-composition-mode))
        (mac-auto-operator-composition-mode))
       ;; Harfbuzz builds do not need font-specific ligature support
-      ;; if they brought in the fe903c5 commit
+      ;; if they are above emacs-27
       ((and (version<= "28.0" emacs-version)
             (string-match-p "HARFBUZZ" system-configuration-features)
             (not (null +prog-ligatures-modes)))

From a897492b99d45b75c8e1711c286ef403e59ed4f5 Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gagbobada+git@gmail.com>
Date: Sun, 26 Apr 2020 12:17:43 +0200
Subject: [PATCH 5/7] Use regexp-opt instead of manual regexes

This helps maintainability tremendously. Thanks wasamasa for the snippet
---
 modules/ui/pretty-code/config.el | 55 +++++++++++++++-----------------
 1 file changed, 26 insertions(+), 29 deletions(-)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index cf02e7ed1..00a68e211 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -100,35 +100,32 @@ Otherwise it builds `prettify-code-symbols-alist' according to
 
 ;;; Automatic font-specific ligatures
 (defvar +prog-ligatures-alist
-  '((?! . "!\\(?:\\(==\\|[!=]\\)[!=]?\\)")
-    (?# . "#\\(?:\\(###?\\|_(\\|[(:=?[_{]\\)[#(:=?[_{]?\\)")
-    (?$ . "$\\(?:\\(>\\)>?\\)")
-    (?% . "%\\(?:\\(%\\)%?\\)")
-    (?& . "&\\(?:\\(&\\)&?\\)")
-    (?* . "*\\(?:\\(\\*\\*\\|[*>]\\)[*>]?\\)")
-    ;; (?* . "*\\(?:\\(\\*\\*\\|[*/>]\\).?\\)")
-    (?+ . "+\\(?:\\([>]\\)>?\\)")
-    ;; (?+ . "+\\(?:\\(\\+\\+\\|[+>]\\).?\\)")
-    (?- . "-\\(?:\\(-[->]\\|<<\\|>>\\|[-<>|~]\\)[-<>|~]?\\)")
-    ;; (?. . "\\.\\(?:\\(\\.[.<]\\|[-.=]\\)[-.<=]?\\)")
-    (?. . "\\.\\(?:\\(\\.<\\|[-=]\\)[-<=]?\\)")
-    (?/ . "/\\(?:\\(//\\|==\\|[=>]\\)[/=>]?\\)")
-    ;; (?/ . "/\\(?:\\(//\\|==\\|[*/=>]\\).?\\)")
-    (?0 . "0\\(?:\\(x[a-fA-F0-9]\\).?\\)")
-    (?: . ":\\(?:\\(::\\|[:<=>]\\)[:<=>]?\\)")
-    (59 . ";\\(?:\\(;\\);?\\)") ;; 59 is ;
-    (?< . "<\\(?:\\(!--\\|\\$>\\|\\*>\\|\\+>\\|-[-<>|]\\|/>\\|<[-<=]\\|=[<>|]\\|==>?\\||>\\||||?\\|~[>~]\\|[$*+/:<=>|~-]\\)[$*+/:<=>|~-]?\\)")
-    (?= . "=\\(?:\\(!=\\|/=\\|:=\\|<<\\|=[=>]\\|>>\\|[=>]\\)[=<>]?\\)")
-    (?> . ">\\(?:\\(->\\|=>\\|>[-=>]\\|[-:=>]\\)[-:=>]?\\)")
-    (?? . "?\\(?:\\([.:=?]\\)[.:=?]?\\)")
-    (91 . "\\[\\(?:\\(|\\)[]|]?\\)") ;; 91 is [
-    ;; (?\ . "\\\\\\(?:\\([\\n]\\)[\\]?\\)")
-    (?^ . "^\\(?:\\(=\\)=?\\)")
-    (?_ . "_\\(?:\\(|_\\|[_]\\)_?\\)")
-    (?w . "w\\(?:\\(ww\\)w?\\)")
-    (?{ . "{\\(?:\\(|\\)[|}]?\\)")
-    (?| . "|\\(?:\\(->\\|=>\\||[-=>]\\||||*>\\|[]=>|}-]\\).?\\)")
-    (?~ . "~\\(?:\\(~>\\|[-=>@~]\\)[-=>@~]?\\)"))
+  `((?! . ,(regexp-opt '("!!" "!=" "!==")))
+    (?# . ,(regexp-opt '("##" "###" "####" "#(" "#:" "#=" "#?" "#[" "#_" "#_(" "#{")))
+    (?$ . ,(regexp-opt '("$>" "$>>")))
+    (?% . ,(regexp-opt '("%%" "%%%")))
+    (?& . ,(regexp-opt '("&&" "&&&")))
+    (?* . ,(regexp-opt '("*" "**" "***" "**/" "*/" "*>")))
+    (?+ . ,(regexp-opt '("+" "++" "+++" "+>")))
+    (?- . ,(regexp-opt '("--" "---" "-->" "-<" "-<<" "->" "->>" "-}" "-~")))
+    (?. . ,(regexp-opt '(".-" ".." "..." "..<" ".=")))
+    (?/ . ,(regexp-opt '("/*" "/**" "//" "///" "/=" "/==" "/>")))
+    (?: . ,(regexp-opt '(":" "::" ":::" ":=" ":<" ":=" ":>")))
+    (?0 . "0\\(?:\\(x[a-fA-F0-9]\\).?\\)") ; Tries to match the x in 0xDEADBEEF
+    ;; (?x . ,(regexp-opt '("x"))) ; Also tries to match the x in 0xDEADBEEF
+    (?\; . ,(regexp-opt '(";;")))
+    (?< . ,(regexp-opt '("<!--" "<$" "<$>" "<*" "<*>" "<+" "<+>" "<-" "<--" "<->" "</" "</>" "<<" "<<-" "<<<" "<<=" "<=" "<=" "<=<" "<==" "<=>" "<>" "<|" "<|>" "<~" "<~~")))
+    (?= . ,(regexp-opt '("=/=" "=:=" "=<<" "==" "===" "==>" "=>" "=>>")))
+    (?> . ,(regexp-opt '(">-" ">->" ">:" ">=" ">=>" ">>" ">>-" ">>=" ">>>")))
+    (?? . ,(regexp-opt '("??" "?." "?:" "?=")))
+    (?\[ . ,(regexp-opt '("[]" "[|]" "[|")))
+    (?\\ . ,(regexp-opt '("\\\\" "\\\\\\" "\\\\n")))
+    (?^ . ,(regexp-opt '("^=" "^==")))
+    (?w . ,(regexp-opt '("www" "wwww")))
+    (?{ . ,(regexp-opt '("{-" "{|" "{||" "{|}" "{||}")))
+    (?| . ,(regexp-opt '("|=" "|>" "||" "||=" "|->" "|=>" "|]" "|}")))
+    (?_ . ,(regexp-opt '("_|_" "__")))
+    (?~ . ,(regexp-opt '("~-" "~=" "~>" "~@" "~~" "~~>"))))
   "An alist containing all the ligatures used when in a `+prog-ligatures-modes' mode.
 
 The car is the character ASCII number, cdr is a regex which will call `font-shape-gstring'

From 4cae60014edb21d28244a414aab1b9eb1186664b Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gagbobada+git@gmail.com>
Date: Mon, 27 Apr 2020 11:11:41 +0200
Subject: [PATCH 6/7] Use EMACS28+ and add emacs-mac source code link

---
 modules/ui/pretty-code/config.el | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/modules/ui/pretty-code/config.el b/modules/ui/pretty-code/config.el
index 00a68e211..ed94d931d 100644
--- a/modules/ui/pretty-code/config.el
+++ b/modules/ui/pretty-code/config.el
@@ -167,7 +167,7 @@ Otherwise it sets the buffer-local composition table to a composition table enha
 
 (use-package! composite
   ;; Starting from emacs "28" because this code breaks without fe903c5
-  :when (and (version<= "28.0" emacs-version) (string-match-p "HARFBUZZ" system-configuration-features))
+  :when (and EMACS28+ (string-match-p "HARFBUZZ" system-configuration-features))
   :init
   (defvar composition-ligature-table (make-char-table nil))
   :config
@@ -177,12 +177,14 @@ Otherwise it sets the buffer-local composition table to a composition table enha
   (set-char-table-parent composition-ligature-table composition-function-table))
 
 ;; The emacs-mac build of Emacs appear to have built-in support for ligatures,
+;; using the same composition-function-table method
+;; https://bitbucket.org/mituharu/emacs-mac/src/26c8fd9920db9d34ae8f78bceaec714230824dac/lisp/term/mac-win.el?at=master#lines-345:805
 ;; so use that instead if this module is enabled.
 (cond ((and IS-MAC (fboundp 'mac-auto-operator-composition-mode))
        (mac-auto-operator-composition-mode))
       ;; Harfbuzz builds do not need font-specific ligature support
       ;; if they are above emacs-27
-      ((and (version<= "28.0" emacs-version)
+      ((and EMACS28+
             (string-match-p "HARFBUZZ" system-configuration-features)
             (not (null +prog-ligatures-modes)))
        nil)

From de0593de38fa484c05c2a417b2adbd9fe7a0a52e Mon Sep 17 00:00:00 2001
From: Gerry Agbobada <gagbobada+git@gmail.com>
Date: Mon, 27 Apr 2020 13:22:15 +0200
Subject: [PATCH 7/7] Add documentation in README

---
 modules/ui/pretty-code/README.org | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/modules/ui/pretty-code/README.org b/modules/ui/pretty-code/README.org
index d22e506f7..231d3e9f0 100644
--- a/modules/ui/pretty-code/README.org
+++ b/modules/ui/pretty-code/README.org
@@ -22,6 +22,8 @@ This module enables ligatures and/or arbitrary symbol substitutions with
 This module has no dedicated maintainers.
 
 ** Module Flags
+*** Font ligatures module flags
+Those flags are ignored on emacs-mac and on other platforms if running emacs 28+ with harfbuzz feature. In those cases, ligatures are handled without needing the extra configuration provided by those flags.
 + =+fira= Enables =Fira Code= ligatures. This requires Fira Code Symbol and a
   patched version of Fira Code (see below).
 + =+hasklig= Enable =Hasklig= ligatures. This requires a patched version of the
@@ -35,8 +37,13 @@ This module has no dedicated maintainers.
 This module installs no packages.
 
 * Prerequisites
-For ligatures to work, you must:
+** Ligatures
+For ligatures to work, you must either have a recent enough version of emacs which will compose ligatures automatically, or use the font specific configurations.
 
+*** Emacs-mac port or Emacs 28+
+Ligatures are handled without needing additional configuration. If this doesn't work, report a bug with your current version of emacs and the ligatures which aren't working.
+
+*** Not Emacs-mac and Emacs <= 27
 1. Enable one of the four ligature font flags: =+fira=, =+hasklig=, =+iosevka=
    or =+pragmata-pro=.
 2. Install the patched version of the associated font with ~M-x
@@ -46,6 +53,15 @@ For ligatures to work, you must:
 
 * TODO Features
 # An in-depth list of features, how to use them, and their dependencies.
+** TODO Mathematical symbols replacement
+** Coding ligatures
+This module includes configuration to compose combinations like =->= or =::= into prettier glyphs (called a ligature). Depending on the current version of emacs, this is implemented in two different ways :
+- prettify-symbols-mode method :: this is the "legacy" method. It uses a font which haves the ligatures as separate unicode symbols, and using prettify-symbols-mode, =->=-like combinations are manually listed and replaced with the correct symbol. The mapping between =->=-like sequences and unicode values in the font are font-specific ; therefore =+fira=, =+iosevka=... files and specific fonts are necessary for it to work.
+- composition-function-table method :: regexes are used to match all the usual sequences which are composed into ligatures. These regexes are passed to emacs directly, which asks Harfbuzz to shape it. Ligatures are obtained automatically depending on the capabilities of the font, and no font-specific configuration is necessary.
+
+Emacs-mac port implements the /composition-function-table/ method in its code, nothing is necessary on Doom side ; otherwise, Doom implements the /composition-function-table/ for emacs 28+ built with Harfbuzz support, and the /prettify-symbols-mode/ method otherwise.
+
+Even though harfbuzz has been included in emacs 27, there is currently a [[https://lists.gnu.org/archive/html/bug-gnu-emacs/2020-04/msg01121.html][bug (#40864)]] which prevents a safe usage of /composition-function-table/ method in emacs 27.
 
 * TODO Configuration
 # How to configure this module, including common problems and how to address them.