Open SVG files in XML mode

Question

When opening a vector icon text file for editing, Emacs first tries to display it as an image. That is wrong ; If the file has errors, Emacs (25.3.2 - x86_64-pc-linux-gnu, GTK+ Version 3.18.9) crashes miserably. Well, I know it has errors, that why I opened it in a text editor in the first place :/

And furthermore, Emacs will hang even if the file doesn't have errors, but just because it cannot render it (like it's just several paths with ids inside a svg grouping tag) which is frustrating to say the least.

How can I make Emacs load text files as text files and not try to render it (because it can't) unless I explicitly told him to?

PS - Yes, I know that I can switch to text-mode by pressing C-c C-c.

What I tried

(add-to-list `auto-mode-alist
             '("\\.svg\\'" . xml-mode))

But no, Emacs still crashes on me upon opening my icons.svg file because it tries to render it as an image (and it's actually several images) when actually it's not its job.

Annex: The SVG code

<svg xmlns="http://www.w3.org/2000/svg">
  <symbol id="cross" viewBox="0 0 20 20">
    <path d="M17.1 5.2l-2.6-2.6-4.6 4.7-4.7-4.7-2.5 2.6 4.7 4.7-4.7 4.7 2.5 2.5 4.7-4.7 4.6 4.7 2.6-2.5-4.7-4.7"/>
  </symbol>
  <symbol id="play" viewBox="0 0 15 15">
    <path d="M690 60H40l330 570L700 60z" />
  </symbol>
</svg>

Answer 1

You'll probably like to either disable auto-image-file-mode or tweak image-file-name-extensions.

BTW, if Emacs crashes or hangs for a particular SVG file, I suggest you M-x report-emacs-bug about it. Maybe there's not much Emacs's code can do about it (e.g. the problem is in the SVG rendering livbrary), but it might be a good reason to change the default so that image-mode is not used by default on SVG files (hell, it might even be a security hole).

Answer 2

I have a solution that does 2 things:

1. Attempt to open any XML file in nXML mode, and this obviously needs to include SVG files.
2. If such a file is an SVG file, then define C-c C-c to image-mode.

For the first item, I use magic-mode-alist to select nxml-mode on some sequences at the beginning of the buffer: <?xml, some DOCTYPE line with XHTML, and <svg followed by a newline character, a space, or >. This will work with SVG files that use an XML prolog or not (I assume no initial spaces, but this could be changed). Here's the code:

(when (boundp 'magic-mode-alist)
  (push '("\\`<\\(\\?xml\\|!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML\\|svg[\n >]\\)"
          . nxml-mode)
        magic-mode-alist)
)

For the second item, I use code for a find-file hook:

(defun my-find-file-hook ()
  (when (and (string= major-mode "nxml-mode")
             (save-excursion
               (and (re-search-forward "<[a-z]" 1024 t)
                    (progn (backward-char)
                           (looking-at "svg[\n >]")))))
    (global-set-key "\C-c\C-c" 'image-mode)))
(add-hook 'find-file-hook 'my-find-file-hook)

If the buffer is in nXML mode, it searches for the root element and if it is svg, then it defines C-c C-c. Note that this is just a heuristic. In particular, a <svg sequence in an initial XML comment could yield a false positive, but I think that this never occurs in practice.