proper descrition of current behaviour

gistfile1.txt

DESCRIPTION OF THE PROBLEM

	use Mojolicious::Lite;
	use Test::Mojo;
	use Test::More;

	get '/test' => { format => 'xxx' };

	my $t = Test::Mojo->new;

	$t->get_ok('/test')->content_is( "xxx\n" );
	$t->get_ok('/test.json')->content_is( "json\n" );
	$t->get_ok('/test?format=json')->content_is( "json\n" );

	done_testing();

	__DATA__
	@@ test.xxx.ep
	xxx

	@@ test.json.ep
	json




	$ perl basic.t
	ok 1 - GET /test
	ok 2 - exact match for content
	ok 3 - GET /test.json
	ok 4 - exact match for content
	ok 5 - GET /test?format=json
	not ok 6 - exact match for content
	#   Failed test 'exact match for content'
	#   at basic.t line 11.
	#          got: 'xxx
	# '
	#     expected: 'json
	# '
	1..6
	# Looks like you failed 1 test of 6.

As you can see default stash value for {format} take precedence over format
query parameter.



DESCRIPTION WHY THIS HAPPEN

Currently while route matching

1. For request with URL path suffix the default {format} stash value is replaced by "placeholder":

    https://github.com/kraih/mojo/blob/master/lib/Mojolicious/Routes/Pattern.pm#L29
    
2. For request without URL path suffix the default {format} stash value **stay on top** of captures 
because captures 'format' is `undef`:

    https://github.com/kraih/mojo/blob/master/lib/Mojolicious/Routes/Pattern.pm#L32
    
Actually here when user requests `undef` format on url path suffix. This `undef` MUST replace default {format}
    
And because this replacement was not done we are fooled here:

    https://github.com/kraih/mojo/blob/master/lib/Mojolicious/Renderer.pm#L30

about that $c->stash->{format} is requested by user (but, as we have seen, that is default {format} stash value)


I. PROPOSITION HOW TO FIX
To prevent that and to keep current behaviour I just split 'default' and 'captured'

    https://github.com/KES777/mojo/pull/36/files#diff-2650135fc08c671d8b875d9b8480f498
    
default value I put into `_sformat`  ( "s" stands for server )
captured value I put into `_cformat` ( "c" stands for client )

When this is done I do content negotiation `around_action` and `before_render` (for actionless route)

    https://github.com/KES777/mojo/pull/36/files#diff-08d2a3a980946f364c7bf445ea6d4a2cR10
    
    
The issue stays for case when exception occur while dispatching:

    https://github.com/kraih/mojo/blob/master/t/mojolicious/exception_lite_app.t#L176
    https://github.com/kraih/mojo/blob/master/t/mojolicious/exception_lite_app.t#L104
    
because {format} is assigned before `before_render` and `around_action` event occour:

    https://github.com/kraih/mojo/blob/master/lib/Mojolicious/Plugin/DefaultHelpers.pm#L110

This can be fixed in two ways:

1. Add bare `around_action`:

    https://github.com/KES777/mojo/pull/36/files#diff-fc5e1c91161f82eb6d5f8cfe15a8aba1R105
    
2. Or delete `DefaultHelpers.pm#L110` line at all. This is safe because we do same later at renderer:

    https://github.com/kraih/mojo/blob/master/lib/Mojolicious/Renderer.pm#L96
    
Which would be better?    
    
    
   
II. PROPOSITION TO IMPROVE FALLBACKS
Working on this patch the propositon was born. If we setup default {format} for application and/or 
route to array this will allow better fallbacks for content negotiation when html is not the default:

    https://github.com/KES777/mojo/pull/36/files#diff-08d2a3a980946f364c7bf445ea6d4a2cR44
    
  # /custom                      -> "json"
  # /custom.html                 -> undef
  # /custom.xml                  -> "xml"
  # /custom.txt                  -> undef
  $r->get( '/custom', { format => [qw( json, xml )] );



Members of the core team. I ask you to include into Mojolicious source core only next change:

    https://github.com/KES777/mojo/pull/36/files#diff-2650135fc08c671d8b875d9b8480f498
    
Hope this description will be sufficent.

Thank you very much for your advices.