[v2] Auto enable pdf-view-dark-minor-mode if the theme is dark

The first attempt at this workaround was
c451c0e3db5b367d191bddf428e38fd8a21c0102 , which did not work
because (my guess) `pdf-tools-enabled-modes` would be evaluated before
the theme was loaded. This is attempt 2, which sets this value in the
`pdf-view-mode` function itself.

This is meant as a workaround for #166 (which see).

Best guess about what is happening and why this workaround works comes
from @d8660091 (lightly edited):

> I'm using M2 and I can reproduce the issue with just the following
> snippets I extracted from pdf-isearch-current-colors, which was
> invoked during a pdf isearch:

    (add-hook 'pdf-tools-enabled-hook
               (lambda ()
                 (pdf-util-face-colors 'pdf-isearch-match nil)
                 (pdf-util-face-colors 'pdf-isearch-lazy nil)))

> And run `pdf-tools-install`

> I tried adding `(sit-for 1)` before `(delete-frame f)`, the crash
> was gone.

> But I am still not sure what's really happening.

> I think `pdf-view-dark-minor-mode` works because new frame is not
> created and `delete-frame` doesn't happen.

If anyone has an idea about what is happening here and what the
correct way to fix it is, please get in touch via the linked issue!

2 files changed, 22 insertions, 19 deletions

diff --git a/lisp/pdf-tools.el b/lisp/pdf-tools.el
index 382d5b6..6211369 100644
--- a/lisp/pdf-tools.el
+++ b/lisp/pdf-tools.el
@@ -134,25 +134,18 @@ In order to customize dark and light colors use
     pdf-virtual-global-minor-mode))
 
 (defcustom pdf-tools-enabled-modes
-  (append '(pdf-history-minor-mode
-            pdf-isearch-minor-mode
-            pdf-links-minor-mode
-            pdf-misc-minor-mode
-            pdf-outline-minor-mode
-            pdf-misc-size-indication-minor-mode
-            pdf-misc-menu-bar-minor-mode
-            pdf-annot-minor-mode
-            pdf-sync-minor-mode
-            pdf-misc-context-menu-minor-mode
-            pdf-cache-prefetch-minor-mode
-            pdf-occur-global-minor-mode)
-          ;; See an interesting discussion at:
-          ;; https://github.com/vedang/pdf-tools/issues/166 about how
-          ;; this avoids a segfault crash in MacOS Ventura. IF you
-          ;; know why this happens, please get in touch via the linked
-          ;; issue.
-          (when (eq 'dark (frame-parameter nil 'background-mode))
-            '(pdf-view-dark-minor-mode)))
+  '(pdf-history-minor-mode
+    pdf-isearch-minor-mode
+    pdf-links-minor-mode
+    pdf-misc-minor-mode
+    pdf-outline-minor-mode
+    pdf-misc-size-indication-minor-mode
+    pdf-misc-menu-bar-minor-mode
+    pdf-annot-minor-mode
+    pdf-sync-minor-mode
+    pdf-misc-context-menu-minor-mode
+    pdf-cache-prefetch-minor-mode
+    pdf-occur-global-minor-mode)
   "A list of automatically enabled minor-modes.
 
 PDF Tools is build as a series of minor-modes.  This variable and
diff --git a/lisp/pdf-view.el b/lisp/pdf-view.el
index 9253721..697fbb7 100644
--- a/lisp/pdf-view.el
+++ b/lisp/pdf-view.el
@@ -332,6 +332,7 @@ regarding display of the region in the later function.")
     map)
   "Keymap used by `pdf-view-mode' when displaying a doc as a set of images.")
 
+(defvar pdf-tools-enabled-modes)
 (define-derived-mode pdf-view-mode special-mode "PDFView"
   "Major mode in PDF buffers.
 
@@ -368,6 +369,15 @@ PNG images in Emacs buffers."
   (if (boundp 'mwheel-coalesce-scroll-events)
       (setq-local mwheel-coalesce-scroll-events t))
 
+  ;; If the Emacs theme is dark, add `pdf-view-dark-minor-mode' to the
+  ;; list of `pdf-tools-enabled-modes'. See an interesting discussion
+  ;; at: https://github.com/vedang/pdf-tools/issues/166 about how this
+  ;; avoids a segfault crash in MacOS Ventura. IF you know why this
+  ;; happens, please get in touch via the linked issue.
+
+  (when (eq 'dark (frame-parameter nil 'background-mode))
+    (add-to-list 'pdf-tools-enabled-modes 'pdf-view-dark-minor-mode))
+
   ;; Clearing overlays
   (add-hook 'change-major-mode-hook
             (lambda ()