bug#33587: [PROPOSED] Default to disabling ImageMagick

[Paul Eggert <eggert@cs.ucla.edu>]

From: Paul Eggert <eggert@Penguin.CS.UCLA.EDU>

ImageMagick has continuing stability and security problems, suggesting
that 'configure' should disable it by default.  See Glenn Morris's notes
at: https://lists.gnu.org/r/emacs-devel/2018-12/msg00036.html
* INSTALL, etc/NEWS: Mention this.
* configure.ac (imagemagick): Default to off.
---
 INSTALL      | 4 +++-
 configure.ac | 2 +-
 etc/NEWS     | 4 ++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/INSTALL b/INSTALL
index 0c56fff6d4..9696904dce 100644
--- a/INSTALL
+++ b/INSTALL
@@ -294,7 +294,9 @@ or more of these options:
   --without-gif          for GIF image support
   --without-png          for PNG image support
   --without-rsvg         for SVG image support
-  --without-imagemagick  for Imagemagick support
+
+Although ImageMagick support is disabled by default due to security
+and stability concerns, you can enable it with --with-imagemagick.
 
 Use --without-toolkit-scroll-bars to disable Motif or Xaw3d scroll bars.
 
diff --git a/configure.ac b/configure.ac
index 8b34c3b658..b70393925a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -354,7 +354,7 @@ AC_DEFUN
 OPTION_DEFAULT_ON([libsystemd],[don't compile with libsystemd support])
 OPTION_DEFAULT_OFF([cairo],[compile with Cairo drawing (experimental)])
 OPTION_DEFAULT_ON([xml2],[don't compile with XML parsing support])
-OPTION_DEFAULT_ON([imagemagick],[don't compile with ImageMagick image support])
+OPTION_DEFAULT_OFF([imagemagick],[compile with ImageMagick image support])
 OPTION_DEFAULT_ON([json], [don't compile with native JSON support])
 
 OPTION_DEFAULT_ON([xft],[don't use XFT for anti aliased fonts])
diff --git a/etc/NEWS b/etc/NEWS
index 6297d07879..07c6f74c44 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -37,6 +37,10 @@ functions 'json-serialize', 'json-insert', 'json-parse-string', and
 'json-parse-buffer' are typically much faster than their Lisp
 counterparts from json.el.
 
+** Emacs no longer defaults to using ImageMagick to display images,
+due to security and stability concerns.  To override the default, use
+'configure --with-imagemagick'.
+
 ** The etags program now uses the C library's regular expression matcher
 when possible, and a compatible regex substitute otherwise.  This will
 let developers maintain Emacs's own regex code without having to also
-- 
2.19.2