mu4e: support icons for mime-types

In mu4e-view-mime-part-action, support icons or, well, "icons".

For this to work user needs to install a package like nerd-icons and set
mu4e-file-name-to-icon-function to #'nerd-icons-icon-for-file. (see
docstring for details)

3 files changed, 192 insertions, 143 deletions

diff --git a/NEWS.org b/NEWS.org
index bcae3e9..e61cc6d 100644
--- a/NEWS.org
+++ b/NEWS.org
@@ -23,6 +23,11 @@
 
    - ~mu4e-compose-post-hook~ only runs once per message (buffer) (1.14.1)
 
+   - You can get icons for MIME-types when using ~mu4e-view-mime-part-action~, by
+     configuring ~mu4e-file-name-to-icon-function~ (see docstring). E.g. when you
+     have the "Nerd Icons" package, you can set this to
+     ~nerd-icons-icon-for-file~. (1.14.1)
+
 *** scm
 
    - added new ~--eval~ command-line option, so you can do e.g.
diff --git a/mu4e/mu4e-helpers.el b/mu4e/mu4e-helpers.el
index 1770562..1925cbc 100644
--- a/mu4e/mu4e-helpers.el
+++ b/mu4e/mu4e-helpers.el
@@ -1,6 +1,6 @@
 ;;; mu4e-helpers.el --- Helper functions -*- lexical-binding: t -*-
 
-;; Copyright (C) 2022-2025 Dirk-Jan C. Binnema
+;; Copyright (C) 2022-2026 Dirk-Jan C. Binnema
 
 ;; Author: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 ;; Maintainer: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
@@ -35,95 +35,55 @@
 
 (require 'mu4e-window)
 (require 'mu4e-config)
+(require 'mailcap)
 
 ;;; Customization
 
-(defcustom mu4e-debug nil
-  "When set to non-nil, log debug information to the mu4e log buffer."
-  :type 'boolean
-  :group 'mu4e)
-
-(defcustom mu4e-completing-read-function #'ido-completing-read
-  "Function to be used to receive user-input during completion.
-
-Suggested possible values are:
- * `completing-read':      Emacs' built-in completion method
- * `ido-completing-read':  dynamic completion within the minibuffer.
-
-The function is used in two contexts -
-1) directly - for instance in when listing _other_ maildirs
-   in `mu4e-ask-maildir'
-2) if `mu4e-read-option-use-builtin' is nil, it is used
-   as part of `mu4e-read-option' in many places.
-
-Set it to `completing-read' when you want to use completion
-frameworks such as Helm, Ivy or Vertico. In that case, you
-might want to add something like the following in your configuration.
+;;; Icons
 
-   (setq mu4e-read-option-use-builtin nil
-         mu4e-completing-read-function \\='completing-read)
-."
-  :type 'function
-  :options '(completing-read ido-completing-read)
-  :group 'mu4e)
+(defcustom mu4e-file-name-to-icon-function nil
+  "Function to return an icon for a file name, or nil.
+When set, this should be a function that takes a file name and
+returns a string (icon) or nil.
 
-(defcustom mu4e-read-option-use-builtin t
-  "Whether to use mu4e's traditional completion for `mu4e-read-option'.
-
-If nil, use the value of `mu4e-completing-read-function', integrated
-into mu4e.
-
-Many of the third-party completion frameworks - such as Helm, Ivy
-and Vertico - influence `completion-read', so to have mu4e follow
-your overall settings, try the equivalent of
-
-   (setq mu4e-read-option-use-builtin nil
-         mu4e-completing-read-function \\='completing-read)
-
-Tastes differ, but without any such frameworks, the unaugmented
-Emacs `completing-read' is rather Spartan."
-  :type 'boolean
-  :group 'mu4e)
+If you have the `nerd-icons' package, you can put
+`nerd-icons-icon-for-file'. If those icons are too big, consider
+installing the special nerd fonts, or perhaps use a value like:
 
-(defcustom mu4e-use-fancy-chars nil
-  "When set, allow fancy (Unicode) characters for marks/threads.
-You can customize the exact fancy characters used with
-`mu4e-marks' and various `mu4e-headers-..-mark' and
-`mu4e-headers..-prefix' variables."
-  :type 'boolean
+   (lambda (name)
+     (nerd-icons-icon-for-file name :height 1.0)))"
+  :type '(choice (const :tag "None" nil) function)
   :group 'mu4e)
 
-;; maybe move the next ones... but they're convenient
-;; here because they're needed in multiple buffers.
-
-(defcustom mu4e-view-auto-mark-as-read t
-  "Automatically mark messages as read when you read them.
-This is the default behavior, but can be turned off, for example
-when using a read-only file-system.
-
-This can also be set to a function; if so, receives a message
-plist which should evaluate to nil if the message should *not* be
-marked as read-only, or non-nil otherwise."
-  :type '(choice
-          boolean
-          function)
-  :group 'mu4e-view)
-
-(defun mu4e-select-other-view ()
-  "Switch between headers view and message view."
-  (interactive)
-  (let* ((other-buf
-          (cond
-           ((mu4e-current-buffer-type-p 'view)
-            (mu4e-get-headers-buffer))
-           ((mu4e-current-buffer-type-p 'headers)
-            (mu4e-get-view-buffer))
-           (t (mu4e-error
-               "This window is neither the headers nor the view window"))))
-         (other-win (and other-buf (get-buffer-window other-buf))))
-    (if (window-live-p other-win)
-        (select-window other-win)
-      (mu4e-message "No window to switch to"))))
+(defcustom mu4e-mime-type-to-icon-function nil
+    "Function to return an icon for a MIME type, or nil.
+When set, this should be a function that takes a MIME-type string
+and returns a string (icon) or nil.
+
+When nil, `mu4e-mime-type-to-icon' falls back to converting the
+MIME type to a file extension and using
+`mu4e-file-name-to-icon-function'."
+    :type '(choice (const :tag "None" nil) function)
+    :group 'mu4e)
+
+(defun mu4e-file-name-to-icon (filename)
+  "Return an icon string for FILENAME, or nil.
+Uses `mu4e-file-name-to-icon-function' if set."
+  (when (and filename mu4e-file-name-to-icon-function)
+    (funcall mu4e-file-name-to-icon-function filename)))
+
+(defun mu4e-mime-type-to-icon (mime-type)
+  "Return an icon string for MIME-TYPE, or nil.
+Uses `mu4e-mime-type-to-icon-function' if set; otherwise
+falls back to `mu4e-file-name-to-icon' with a dummy filename
+derived from the MIME type via `mailcap-mime-type-to-extension'."
+  (when mime-type
+    (or (and mu4e-mime-type-to-icon-function
+             (funcall mu4e-mime-type-to-icon-function mime-type))
+        (let ((ext (mailcap-mime-type-to-extension mime-type)))
+          (when ext
+            (mu4e-file-name-to-icon
+             (concat "file." (symbol-name ext))))))))
 
 ;;; Messages, warnings and errors
 (defun mu4e-format (frm &rest args)
@@ -163,6 +123,48 @@ Does a local-exit and does not return."
 
 ;;; Reading user input
 
+(defcustom mu4e-completing-read-function #'ido-completing-read
+  "Function to be used to receive user-input during completion.
+
+Suggested possible values are:
+ * `completing-read':      Emacs' built-in completion method
+ * `ido-completing-read':  dynamic completion within the minibuffer.
+
+The function is used in two contexts -
+1) directly - for instance in when listing _other_ maildirs
+   in `mu4e-ask-maildir'
+2) if `mu4e-read-option-use-builtin' is nil, it is used
+   as part of `mu4e-read-option' in many places.
+
+Set it to `completing-read' when you want to use completion
+frameworks such as Helm, Ivy or Vertico. In that case, you
+might want to add something like the following in your configuration.
+
+   (setq mu4e-read-option-use-builtin nil
+         mu4e-completing-read-function \\='completing-read)
+."
+  :type 'function
+  :options '(completing-read ido-completing-read)
+  :group 'mu4e)
+
+(defcustom mu4e-read-option-use-builtin t
+  "Whether to use mu4e's traditional completion for `mu4e-read-option'.
+
+If nil, use the value of `mu4e-completing-read-function', integrated
+into mu4e.
+
+Many of the third-party completion frameworks - such as Helm, Ivy
+and Vertico - influence `completion-read', so to have mu4e follow
+your overall settings, try the equivalent of
+
+   (setq mu4e-read-option-use-builtin nil
+         mu4e-completing-read-function \\='completing-read)
+
+Tastes differ, but without any such frameworks, the unaugmented
+Emacs `completing-read' is rather Spartan."
+  :type 'boolean
+  :group 'mu4e)
+
 (defun mu4e--plist-get (lst prop)
   "Get PROP from plist LST and raise an error if not present."
   (or (plist-get lst prop)
@@ -322,6 +324,11 @@ Function returns the value (cdr) of the matching cell."
 
 ;;; Logging / debugging
 
+(defcustom mu4e-debug nil
+  "When set to non-nil, log debug information to the mu4e log buffer."
+  :type 'boolean
+  :group 'mu4e)
+
 (defconst mu4e--log-max-size 1000000
   "Max number of characters to keep around in the log buffer.")
 (defconst mu4e--log-buffer-name "*mu4e-log*"
@@ -527,6 +534,46 @@ Or go to the top level if there is none."
           ('mu4e-view-mode    "(mu4e)Message view")
           (_                  "mu4e"))))
 
+(defcustom mu4e-use-fancy-chars nil
+  "When set, allow fancy (Unicode) characters for marks/threads.
+You can customize the exact fancy characters used with
+`mu4e-marks' and various `mu4e-headers-..-mark' and
+`mu4e-headers..-prefix' variables."
+  :type 'boolean
+  :group 'mu4e)
+
+;; maybe move the next ones... but they're convenient
+;; here because they're needed in multiple buffers.
+
+(defcustom mu4e-view-auto-mark-as-read t
+  "Automatically mark messages as read when you read them.
+This is the default behavior, but can be turned off, for example
+when using a read-only file-system.
+
+This can also be set to a function; if so, receives a message
+plist which should evaluate to nil if the message should *not* be
+marked as read-only, or non-nil otherwise."
+  :type '(choice
+          boolean
+          function)
+  :group 'mu4e-view)
+
+(defun mu4e-select-other-view ()
+  "Switch between headers view and message view."
+  (interactive)
+  (let* ((other-buf
+          (cond
+           ((mu4e-current-buffer-type-p 'view)
+            (mu4e-get-headers-buffer))
+           ((mu4e-current-buffer-type-p 'headers)
+            (mu4e-get-view-buffer))
+           (t (mu4e-error
+               "This window is neither the headers nor the view window"))))
+         (other-win (and other-buf (get-buffer-window other-buf))))
+    (if (window-live-p other-win)
+        (select-window other-win)
+      (mu4e-message "No window to switch to"))))
+
 ;;; Emacs bookmarks
 (defcustom mu4e-emacs-bookmark-policy 'message
   "The policy to decide what kind of Emacs bookmark to create.
diff --git a/mu4e/mu4e-mime-parts.el b/mu4e/mu4e-mime-parts.el
index 2a01dee..119e74f 100644
--- a/mu4e/mu4e-mime-parts.el
+++ b/mu4e/mu4e-mime-parts.el
@@ -176,57 +176,51 @@ Note: this is not compatible with `helm-mode'."
   :lighter ""
   :keymap mu4e-view-completion-minor-mode-map)
 
-(defun mu4e--part-annotation (candidate part type longest-filename)
-  "Calculate the annotation candidates as per annotation.
-I.e., `:annotation-function' (see `completion-extra-properties')
-
-CANDIDATE is the value to annotate.
-
-PART is the matching MIME-part for the annotation, (as per
-`mu4e-view-mime-part').
-
-TYPE is the of what to annotate, a symbol, either ATTACHMENT or
-MIME-PART.
-
-LONGEST-FILENAME is the length of the longest filename; this
-information' is used for alignment."
-  (let* ((filename (propertize (or  (plist-get part :filename) "")
-                               'face 'mu4e-header-key-face))
-         (mimetype (propertize (or (plist-get part :mime-type) "")
-                               'face 'mu4e-header-value-face))
-         (target (propertize (or  (plist-get part :target-dir) "")
-                             'face 'mu4e-system-face)))
-
-    ;; Sadly, we need too align by hand; this makes some assumptions
-    ;; such a mono-type font and enough space in the minibuffer; and
-    ;; mixing values and representation; ideally Emacs would allow
-    ;; just take some columns and align them (since it knows the display
-    ;; details).
-
-    (pcase type
-      ('attachment
-       ;; in case we're annotating an attachment, the filename is
-       ;; the candidate (completion), so we don't need it in the
-       ;; the annotation. We just need to but some space at beginning
-       ;; for alignment
-       (concat
-        (make-string  (-  (+ longest-filename 2)
-                          (length (format "%s" candidate))) ?\s)
-        (format "%20s" mimetype)
-        "       "
-        (format "%s" (concat "-> " target))))
-      ('mime-part
-       ;; when we're annotating a mime-part, the candidate is just a number,
-       ;; and the filename is part of the annotation.
-       (concat
-        "  "
-        filename
-        (make-string  (-  (+ longest-filename 2)
-                          (length filename)) ?\s)
-        (format "%20s" mimetype)
-        "       "
-        (format "%s" (concat "-> " target))))
-      (_ (mu4e-error "Unsupported annotation type %s" type)))))
+(defun mu4e--part-affixation (candidates-alist type longest-filename completions)
+  "Calculate the affixation for COMPLETIONS.
+I.e., `:affixation-function' (see `completion-extra-properties').
+
+Returns a list of (CANDIDATE PREFIX SUFFIX) triples.
+
+CANDIDATES-ALIST is the full alist of candidates (id . part).
+TYPE is what to annotate, a symbol, either ATTACHMENT or MIME-PART.
+LONGEST-FILENAME is the length of the longest filename; used for alignment.
+COMPLETIONS is the list of completion strings to affixate."
+  (mapcar
+   (lambda (candidate)
+     (let* ((part (cdr-safe (assoc candidate candidates-alist)))
+            (raw-filename (or (plist-get part :filename) ""))
+            (filename (propertize raw-filename
+                                 'face 'mu4e-header-key-face))
+            (mimetype (propertize (or (plist-get part :mime-type) "")
+                                 'face 'mu4e-header-value-face))
+            (target (propertize (or (plist-get part :target-dir) "")
+                                'face 'mu4e-system-face))
+            (icon (or (mu4e-mime-type-to-icon
+                      (plist-get part :mime-type))
+                     (mu4e-file-name-to-icon raw-filename)))
+            (prefix (if icon (concat icon " ") ""))
+            (suffix
+             (pcase type
+               ('attachment
+                (concat
+                 (make-string (- (+ longest-filename 2)
+                                 (length (format "%s" candidate))) ?\s)
+                 (format "%20s" mimetype)
+                 "       "
+                 (format "%s" (concat "-> " target))))
+               ('mime-part
+                (concat
+                 "  "
+                 filename
+                 (make-string (- (+ longest-filename 2)
+                                 (length filename)) ?\s)
+                 (format "%20s" mimetype)
+                 "       "
+                 (format "%s" (concat "-> " target))))
+               (_ (mu4e-error "Unsupported annotation type %s" type)))))
+       (list candidate prefix suffix)))
+   completions))
 
 (defvar helm-comp-read-use-marked)
 (defun mu4e--completing-read-real (prompt candidates multi)
@@ -257,7 +251,7 @@ the current message.
 - PROMPT is a string informing the user what to complete
 - CANDIDATES is an alist of candidates of the form
     (id . part)
-- TYPE is the annotation type to uses as per `mu4e--part-annotation'.
+- TYPE is the annotation type to use as per `mu4e--part-affixation'.
 Optionally,
 - MULTI if t, allow for completing _multiple_ candidates."
   (cl-assert candidates)
@@ -265,20 +259,23 @@ Optionally,
                             (seq-map (lambda (c)
                                        (length (plist-get (cdr c) :filename)))
                                      candidates)))
-         (annotation-func (lambda (candidate)
-                            (mu4e--part-annotation candidate
-                                                   (cdr-safe
-                                                    (assoc candidate candidates))
-                                                   type longest-filename)))
+         (affixation-func (lambda (completions)
+                            (mu4e--part-affixation candidates type
+                                                   longest-filename
+                                                   completions)))
+         (table (lambda (string pred action)
+                  (if (eq action 'metadata)
+                      `(metadata
+                        (category . mime-part)
+                        (affixation-function . ,affixation-func))
+                    (complete-with-action action candidates string pred))))
          (completion-extra-properties
-          `(;; :affixation-function requires emacs 28
-            :annotation-function ,annotation-func
-            :exit-function (lambda (_a _b) (setq mu4e--completions-table nil)))))
+          `(:exit-function (lambda (_a _b) (setq mu4e--completions-table nil)))))
     (setq mu4e--completions-table candidates)
     (minibuffer-with-setup-hook
         (lambda ()
           (mu4e-view-completion-minor-mode))
-      (mu4e--completing-read-real prompt candidates multi))))
+      (mu4e--completing-read-real prompt table multi))))
 
 (defun mu4e-view-save-attachments (&optional ask-dir)
   "Save files from the current view buffer.