gnu: Add emacs-gtk-look.

* gnu/packages/emacs.scm (emacs-gtk-look): New variable.

gnu/packages/emacs.scm

@@ -12500,3 +12500,41 @@ fix its formatting.  @command{clang-format} is a tool that formats C/C++/Obj-C
 code according to a set of style options, see
 @url{http://clang.llvm.org/docs/ClangFormatStyleOptions.html}.")
       (license license:gpl3+))))
+
+(define-public emacs-gtk-look
+  (package
+    (name "emacs-gtk-look")
+    (version "29")
+    (source (origin
+              (method url-fetch)
+              (uri "https://download.tuxfamily.org/user42/gtk-look.el")
+              (sha256
+               (base32
+                "14p2nwrd51cr1v06fxbjjn6jdrkf9d6vcxhmscm0kl677s25ypsp"))))
+    (build-system emacs-build-system)
+    (arguments
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'configure
+           (lambda _
+             ;; File is read-only.
+             (chmod "gtk-look.el" #o644)
+             (emacs-substitute-variables "gtk-look.el"
+               ("gtk-lookup-devhelp-indices"
+                '(list (expand-file-name "~/.guix-profile/share/gtk-doc/html/*/*.devhelp*"))))
+             #t)))))
+    (home-page "http://user42.tuxfamily.org/gtk-look/index.html")
+    (synopsis "Find and display HTML documentation for GTK, GNOME and Glib")
+    (description "@command{gtk-look} finds and displays HTML documentation for
+GTK, GNOME and Glib functions and variables in Emacs, similar to what
+info-lookup-symbol does for info files (C-h S).  The documentation is expected
+to be devhelp indexes with HTML files.  The location of the indexes can be
+customized.  In addition to C code development @command{gtk-look} is good for
+
+@itemize
+@item @command{perl-gtk2}, recognising class funcs like
+@command{Gtk2::Label->new} and bare method names like @command{set_text}.
+@item @command{guile-gnome}, recognising methods like @command{set-text} and
+classes like @command{<gtk-window>}.
+@end itemize\n")
+    (license license:gpl3+)))