feat() Use magick by default, fall back to convert if missing

This handles IM7 deprecation warnings and allows JPT to work on Windows, without breaking it on distros that ship IM6 such as ubuntu.

* replaced convert with magick
* Updated command? for Windows
* Adding Fallback to convert

ubuntu uses IM6 by default which doesn't support magick

Author: MUmarShahbaz

docs/users/presets/image_formats.md

@@ -17,5 +17,5 @@ used**. `original` does what you'd expect. To supply webp, you must have an
 imagemagick webp delegate installed. (Most package managers just name it 'webp')
 
 _Supported formats are anything which imagemagick supports, and has an installed
-delegate. See a list by running `$ convert --version`_.
+delegate. See a list by running `$ magick --version`_.
 

lib/jekyll_picture_tag/parsers/image_backend.rb

@@ -28,7 +28,13 @@ def vips_formats
 
       # Returns an array of formats that imagemagick can handle.
       def magick_formats
-        if command?('convert')
+        if command?('magick')
+          @magick_formats ||= `magick -version`
+                              .scan(/Delegates.*/)
+                              .first
+                              .delete_prefix('Delegates (built-in):')
+                              .split
+        elsif command?('convert')
           @magick_formats ||= `convert -version`
                               .scan(/Delegates.*/)
                               .first
@@ -56,7 +62,7 @@ def error_string(format)
                else
                  'Libvips is not installed.'
                end
-        str << if command?('convert')
+        str << if command?('magick') || command?('convert')
                  "Imagemagick (installed) supports: \"#{magick_formats.join(', ')}\"."
                else
                  'Imagemagick is not installed.'
@@ -69,7 +75,12 @@ def alternates
       end
 
       def command?(command)
-        system("which #{command} > /dev/null 2>&1")
+        is_windows = RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/
+        if is_windows
+          system("where #{command} > NUL 2>&1")
+        else
+          system("which #{command} > /dev/null 2>&1")
+        end
       end
     end
   end

test/test_helper.rb

@@ -49,7 +49,8 @@ def temp_dir(*descendents)
   # them doesn't support some image format. This returns an array of image
   # formats which we care about, and which are locally supported.
   def supported_formats
-    output = `vips --list` + `convert --version`
+    magick_command = command?('magick') ? `magick` : `convert`
+    output = `vips --list` + `#{magick_command} --version`
 
     formats = %w[jpg png webp gif jp2 avif].select do |format|
       output.include? format
@@ -60,4 +61,13 @@ def supported_formats
 
     formats
   end
+
+  def command?(command)
+    is_windows = RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/
+    if is_windows
+      system("where #{command} > NUL 2>&1")
+    else
+      system("which #{command} > /dev/null 2>&1")
+    end
+  end
 end