Merge remote branch 'smcv/ready/sort-package'

[git.ikiwiki.info.git] / doc / plugins / contrib / field / discussion.mdwn

diff --git a/doc/plugins/contrib/field/discussion.mdwn b/doc/plugins/contrib/field/discussion.mdwn
index fc1759fab5560995b7b0acfb2864b5d01907feb7..2ea195e5b69512ad700a4f399f9e59c219799401 100644 (file)
--- a/doc/plugins/contrib/field/discussion.mdwn
+++ b/doc/plugins/contrib/field/discussion.mdwn
@@ -9,6 +9,79 @@ with IkiWiki's use of `<TMPL_VAR AUTHOR>` for the author of the *page*
 `<TMPL_VAR FIELD_AUTHOR>` or something? (For those who want the current
 behaviour, an auxiliary plugin would be easy.)
 
 `<TMPL_VAR FIELD_AUTHOR>` or something? (For those who want the current
 behaviour, an auxiliary plugin would be easy.)
 

+> No, please.  The idea is to be *able* to override field names if one wishes to, and choose, for yourself, non-colliding field names if one wishes not to.  I don't wish to lose the power of being able to, say, define a page title with YAML format if I want to, or to write a site-specific plugin which calculates a page title, or other nifty things.
+>It's not like one is going to lose the fields defined by the meta plugin; if "author" is defined by \[[!meta author=...]] then that's what will be found by "field" (provided the "meta" plugin is registered; that's what the "field_register" option is for).
+>--[[KathrynAndersen]]
+
+>> Hmm. I suppose if you put the title (or whatever) in the YAML, then
+>> "almost" all the places in IkiWiki that respect titles will do the
+>> right thing due to the pagetemplate hook, with the exception being
+>> anything that has special side-effects inside `meta` (like `date`),
+>> or anything that looks in `$pagestate{foo}{meta}` directly
+>> (like `map`). Is your plan that `meta` should register itself by
+>> default, and `map` and friends should be adapted to
+>> work based on `getfield()` instead of `$pagestate{foo}{meta}`, then?
+
+>>> Based on `field_get_value()`, yes.  That would be my ideal.  Do you think I should implement that as an ikiwiki branch? --[[KathrynAndersen]]
+
+>>>> This doesn't solve cases where certain fields are treated specially; for
+>>>> instance, putting a `\[[!meta permalink]]` on a page is not the same as
+>>>> putting it in `ymlfront` (in the latter case you won't get your
+>>>> `<link>` header), and putting `\[[!meta date]]` is not the same as putting
+>>>> `date` in `ymlfront` (in the latter case, `%pagectime` won't be changed).
+>>>>
+>>>> One way to resolve that would be to have `ymlfront`, or similar, be a
+>>>> front-end for `meta` rather than for `field`, and call
+>>>> `IkiWiki::Plugin::meta::preprocess` (or a refactored-out function that's
+>>>> similar).
+>>>>
+>>>> There are also some cross-site scripting issues (see below)... --[[smcv]]
+
+>> (On the site I mentioned, I'm using an unmodified version of `field`,
+>> and currently working around the collision by tagging books' pages
+>> with `bookauthor` instead of `author` in the YAML.) --s
+
+>> Revisiting this after more thought, the problem here is similar to the
+>> possibility that a wiki user adds a `meta` shortcut
+>> to [[shortcuts]], or conversely, that a plugin adds a `cpan` directive
+>> that conflicts with the `cpan` shortcut that pages already use. (In the
+>> case of shortcuts, this is resolved by having plugin-defined directives
+>> always win.) For plugin-defined meta keywords this is the plugin
+>> author's/wiki admin's problem - just don't enable conflicting plugins! -
+>> but it gets scary when you start introducing things like `ymlfront`, which
+>> allow arbitrary, wiki-user-defined fields, even ones that subvert
+>> other plugins' assumptions.
+>>
+>> The `pagetemplate` hook is particularly alarming because page templates are
+>> evaluated in many contexts, not all of which are subject to the
+>> htmlscrubber or escaping; because the output from `field` isn't filtered,
+>> prefixed or delimited, when combined with an arbitrary-key-setting plugin
+>> like `ymlfront` it can interfere with other plugins' expectations
+>> and potentially cause cross-site scripting exploits. For instance, `inline`
+>> has a `pagetemplate` hook which defines the `FEEDLINKS` template variable
+>> to be a blob of HTML to put in the `<head>` of the page. As a result, this
+>> YAML would be bad:
+>>
+>>     ---
+>>     FEEDLINKS: <script>alert('code injection detected')</script>
+>>     ---
+>>
+>> (It might require a different case combination due to implementation
+>> details, I'm not sure.)
+>>
+>> It's difficult for `field` to do anything about this, because it doesn't
+>> know whether a field is meant to be plain text, HTML, a URL, or something
+>> else.
+>>
+>> If `field`'s `pagetemplate` hook did something more limiting - like
+>> only emitting template variables starting with `field_`, or from some
+>> finite set, or something - then this would cease to be a problem, I think?
+>>
+>> `ftemplate` and `getfield` don't have this problem, as far as I can see,
+>> because their output is in contexts where the user could equally well have
+>> written raw HTML directly; the user can cause themselves confusion, but
+>> can't cause harmful output. --[[smcv]]
+

 From a coding style point of view, the `$CamelCase` variable names aren't
 IkiWiki style, and the `match_foo` functions look as though they could benefit
 from being thin wrappers around a common `&IkiWiki::Plugin::field::match`
 From a coding style point of view, the `$CamelCase` variable names aren't
 IkiWiki style, and the `match_foo` functions look as though they could benefit
 from being thin wrappers around a common `&IkiWiki::Plugin::field::match`


@@ -17,13 +90,22 @@ function (see `meta` for a similar approach).
 I think the documentation would probably be clearer in a less manpage-like
 and more ikiwiki-like style?
 
 I think the documentation would probably be clearer in a less manpage-like
 and more ikiwiki-like style?
 

+> I don't think ikiwiki *has* a "style" for docs, does it?  So I followed the Perl Module style. And I'm rather baffled as to why having the docs laid out in clear sections... make them less clear. --[[KathrynAndersen]]
+
+>> I keep getting distracted by the big shouty headings :-)
+>> I suppose what I was really getting at was that when this plugin
+>> is merged, its docs will end up split between its plugin
+>> page, [[plugins/write]] and [[ikiwiki/PageSpec]]; on some of the
+>> contrib plugins I've added I've tried to separate the docs
+>> according to how they'll hopefully be laid out after merge. --s
+

 If one of my branches from [[todo/allow_plugins_to_add_sorting_methods]] is
 accepted, a `field()` cmp type would mean that [[plugins/contrib/report]] can
 stop reimplementing sorting. Here's the implementation I'm using, with
 your "sortspec" concept (a sort-hook would be very similar): if merged,
 I think it should just be part of `field` rather than a separate plugin.
 
 If one of my branches from [[todo/allow_plugins_to_add_sorting_methods]] is
 accepted, a `field()` cmp type would mean that [[plugins/contrib/report]] can
 stop reimplementing sorting. Here's the implementation I'm using, with
 your "sortspec" concept (a sort-hook would be very similar): if merged,
 I think it should just be part of `field` rather than a separate plugin.
 

-       # Copyright © 2010 Simon McVittie, released under GNU LGPL >= 2.1
+       # Copyright © 2010 Simon McVittie, released under GNU GPL >= 2

        package IkiWiki::Plugin::fieldsort;
        use warnings;
        use strict;
        package IkiWiki::Plugin::fieldsort;
        use warnings;
        use strict;


@@ -42,17 +124,15 @@ I think it should just be part of `field` rather than a separate plugin.
                        },
        }
 
                        },
        }
 

-       package IkiWiki::PageSpec;
+       package IkiWiki::SortSpec;

 
 

-       sub check_cmp_field {
+       sub cmp_field {

                if (!length $_[0]) {
                        error("sort=field requires a parameter");
                }
                if (!length $_[0]) {
                        error("sort=field requires a parameter");
                }

-       }

 
 

-       sub cmp_field {
-               my $left = IkiWiki::Plugin::field::field_get_value($_[2], $_[0]);
-               my $right = IkiWiki::Plugin::field::field_get_value($_[2], $_[1]);
+               my $left = IkiWiki::Plugin::field::field_get_value($_[0], $a);
+               my $right = IkiWiki::Plugin::field::field_get_value($_[0], $b);

 
                $left = "" unless defined $left;
                $right = "" unless defined $right;
 
                $left = "" unless defined $left;
                $right = "" unless defined $right;


@@ -60,3 +140,87 @@ I think it should just be part of `field` rather than a separate plugin.
        }
 
        1;
        }
 
        1;

+
+----
+
+Disclaimer: I've only looked at this plugin and ymlfront, not other related
+stuff yet. (I quite like ymlfront, so I looked at this as its dependency. :)
+I also don't want to annoy you with a lot of design discussion 
+if your main goal was to write a plugin that did exactly what you wanted.
+
+My first question is: Why we need another plugin storing metadata
+about the page, when we already have the meta plugin? Much of the
+complication around the field plugin has to do with it accessing info
+belonging to the meta plugin, and generalizing that to be able to access
+info stored by other plugins too. (But I don't see any other plugins that
+currently store such info). Then too, it raises points of confusion like
+smcv's discuission of field author vs meta author above. --[[Joey]] 
+
+> The point is exactly in the generalization, to provide a uniform interface for accessing structured data, no matter what the source of it, whether that be the meta plugin or some other plugin.
+
+> There were a few reasons for this:
+
+>1. In converting my site over from PmWiki, I needed something that was equivalent to PmWiki's Page-Text-Variables (which is how PmWiki implements structured data).
+>2. I also wanted an equivalent of PmWiki's Page-Variables, which, rather than being simple variables, are the return-value of a function.  This gives one a lot of power, because one can do calculations, derive one thing from another.  Heck, just being able to have a "basename" variable is useful.
+>3. I noticed that in the discussion about structured data, it was mired down in disagreements about what form the structured data should take; I wanted to overcome that hurdle by decoupling the form from the content.
+>4. I actually use this to solve (1), because, while I do use ymlfront, initially my pages were in PmWiki format (I wrote (another) unreleased plugin which parses PmWiki format) including PmWiki's Page-Text-Variables for structured data.  So I needed something that could deal with multiple formats.
+
+> So, yes, it does cater to mostly my personal needs, but I think it is more generally useful, also.
+> --[[KathrynAndersen]]
+
+>> Is it fair to say, then, that `field`'s purpose is to take other
+>> plugins' arbitrary per-page data, and present it as a single
+>> merged/flattened string => string map per page? From the plugins
+>> here, things you then use that merged map for include:
+>>
+>> * sorting - stolen by [[todo/allow_plugins_to_add_sorting_methods]]
+>> * substitution into pages with Perl-like syntax - `getfield`
+>> * substitution into wiki-defined templates - the `pagetemplate`
+>>   hook
+>> * substitution into user-defined templates - `ftemplate`
+>>
+>> As I mentioned above, the flattening can cause collisions (and in the
+>> `pagetemplate` case, even security problems).
+>>
+>> I wonder whether conflating Page Text Variables with Page Variables
+>> causes `field` to be more general than it needs to be?
+>> To define a Page Variable (function-like field), you need to write
+>> a plugin containing that Perl function; if we assume that `field`
+>> or something resembling it gets merged into ikiwiki, then it's
+>> reasonable to expect third-party plugins to integrate with whatever
+>> scaffolding there is for these (either in an enabled-by-default
+>> plugin that most people are expected to leave enabled, like `meta`
+>> now, or in the core), and it doesn't seem onerous to expect each
+>> plugin that wants to participate in this mechanism to have code to
+>> do so. While it's still contrib, `field` could just have a special case
+>> for the meta plugin, rather than the converse?
+>>
+>> If Page Text Variables are limited to being simple strings as you
+>> suggest over in [[forum/an_alternative_approach_to_structured_data]],
+>> then they're functionally similar to `meta` fields, so one way to
+>> get their functionality would be to extend `meta` so that
+>>
+>>     \[[!meta badger="mushroom"]]
+>>
+>> (for an unrecognised keyword `badger`) would store
+>> `$pagestate{$page}{meta}{badger} = "mushroom"`? Getting this to
+>> appear in templates might be problematic, because a naive
+>> `pagetemplate` hook would have the same problem that `field` combined
+>> with `ymlfront` currently does.
+>>
+>> One disadvantage that would appear if the function-like and
+>> meta-like fields weren't in the same namespace would be that it
+>> wouldn't be possible to switch a field from being meta-like to being
+>> function-like without changing any wiki content that referenced it.
+>>
+>> Perhaps meta-like fields should just *be* `meta` (with the above
+>> enhancement), as a trivial case of function-like fields? That would
+>> turn `ymlfront` into an alternative syntax for `meta`, I think?
+>> That, in turn, would hopefully solve the special-fields problem,
+>> by just delegating it to meta. I've been glad of the ability to define
+>> new ad-hoc fields with this plugin without having to write an extra plugin
+>> to do so (listing books with a `bookauthor` and sorting them by
+>> `"field(bookauthor) title"`), but that'd be just as easy if `meta`
+>> accepted ad-hoc fields?
+>>
+>> --[[smcv]]