#======================================================================== # # TODO # # DESCRIPTION # TODO list for the Template Toolkit version 2.07, containing # known bugs, limitations, planned enhancements, long term visions # and a few whacky ideas. # # AUTHOR # Andy Wardley <abw@kfs.org> # #------------------------------------------------------------------------ # $Id: TODO.tt2,v 1.13 2001/12/14 11:08:33 abw Exp $ #======================================================================== #------------------------------------------------------------------------ # Miscellaneous #------------------------------------------------------------------------ * mylist.sort.uniq * Errors thrown via the Error module are not correctly caught. I looked at this briefly but the problem wasn't immediately obvious and needs some more considered investigation. There are also problems with CGI::Carp throwing errors that don't get properly caught. * The 'eval' filter leaks memory, as reported by Colin Johnson. The filter subroutine created contains a reference to the context and then gets cached in the FILTER_CACHE item of the context. Hey presto - circular references. The reset() method should probably clear the FILTER_CACHE. Also need to check the plugins cache for similar problems. * The handling of the DELIMITER parameter could be improved. At the moments it's hardcoded and hacked to Do The Right Thing for Win32 but I'd prefer it to Do The Good Thing. * If you use 'ttree' with a COMPILE_EXT or COMPILE_DIR option then templates in the 'lib' directories will be compiled, but those in the src directories will not. This is because ttree does a chdir() to the src directory and processes files as './myfile'. TT doesn't compile RELATIVE files by default. * No recursion checking is performed for BLOCKs, only Template::Document instances. This is probably the way it will stay (unless anyone shouts loudly enough) but it should be documented anyway. STOP PRESS: I had an idea that bare BLOCK subs should be blessed into Template::Document class to allow $template->process() to be called regardless. Template::Document methods would need to test $self for CODE/HASH and Do The Right Thing. This would then allow recursion testing for BLOCKs as well as Template::Document objects. * It would be nice if there was an option so that the files generated under the COMPILE_DIR are relative to the INCLUDE_PATH and not absolute. This could cause potential conflicts (e.g. if INCLUDE_PATH changes between sessions and the same files in different INCLUDE_PATH dirs maps to the samed compiled version) but is convenient for those times when you know that's not going to be a problem. * Richard Tietjen's patch for stash replace. Allows back references (e.g. $1) but it would be nice to find a rock-solid way to implement it without relying on unusual ^A delimiter character. * Further to the above, Craig Barratt has this solution which will be going into the next verion (2.05b) unless anyone has any further suggestions to make before then. It would be great if replace handled backreferences. I don't like the ^A solution since the string could contain ^A, plus it is a security hole. The attempt I posted only works for up to 9 backreferences and doesn't handle an escaped '\$' and uses nested evals: $str =~ s{$search}{ my $r = $replace; my @d = (0, $1, $2, $3, $4, $5, $6, $7, $8, $9); $r =~ s/\$(\d+)/$d[$1]/eg; $r; }eg; I wish there was a perl predefined variable array containing all the backreferences (is there one?). You can avoid the hard-coded limit of 9 with extra evals, and a bit of work on the re could handle the escaped '\$' case, so maybe that would be good enough. * Craig also notes, in fixing the problem with NEXT not working inside SWITCH (see Changes v2.04): By the way, I came across another arcane bug: NEXT FOREACH k = [1]; is legal syntax but is an infinite loop, since $_[0]->{ INFOR } in Parser.yp is not set when the NEXT is parsed, so it generates a plain "next;" rather than calling $factor->next(). I don't see an easy, clean fix. #------------------------------------------------------------------------ # Documentation #------------------------------------------------------------------------ * Extend the FAQ. * Document the Splash! library properly, once the interface is a little more settled. * Examples for libraries (HTML, Splash & PostScript) should be integrated into the documentation. #------------------------------------------------------------------------ # Directives #------------------------------------------------------------------------ * A 'FOR', like 'FOREACH' but without using an iterator. You wouldn't get the 'loop' reference to test 'first', 'last', etc., against, but it would be faster for those cases when you didn't need it. This will likely be implemented as a facility feature (see later). * PRINT should be defined as a new directive, doing what the print() method of Template::View currently does (the Right Thing). [% PRINT node %] === [% tt.view.print(node) %] NOTE TO SELF: this is a Very Good Idea [tm]. PRINT becomes the way to display a data structure (e.g. hash, list, XML element, MyThingy, database record, etc.) in an "intelligent" fashion. Implemented underneath via the current default VIEW. * ARGS. There may be a requirement for reusable template components to define what variables they plan to use. This would allow some optimisation and also possibly help to avoid global variable clashes. Would also be a useful "comment" directive for human readers and maybe also help in debugging (WARNING: expected 'title' argument). [% ARGS title # no default bgcol='#ffffff' # default value %] #------------------------------------------------------------------------ # Stash #------------------------------------------------------------------------ * The XS Stash does not work with tied hashes (e.g. DBI.tie). Also note that enabling the XS Stash cause all the Template::* modules to be installed in an architecture-dependant directory. For info, see http://www.tt2.org/pipermail/templates/2001-September/001568.html * Jonas Liljegren reports a segfault when using the XS Stash under Apache/mod_perl with certain undefined variables. At the time of writing detail is scarce. Check the mailing list for further details. * Stas Bekman raised the issue of the Stash not being able to correctly differentiate between scalar/list context and in particular, the cgi.param examples not working as expected. This is fixed in v3 and in Craig's Stash/Context.pm which does the right lookahead to allow 'scalar' and 'list' postfix operators. e.g. cgi.param.list * Have stash, etc., add current template name/line when reporting errors. (may be tricky under the current implementation) #------------------------------------------------------------------------ # Parser #------------------------------------------------------------------------ * Lists don't accept arbitrary expressions as elements. In other words you can't do this: [% foo(bar + 1) %]. This has been fixed in the v3 parser. See http://www.tt2.org/v3/ * The parser isn't as intelligent as it could be about blocks of template code commented out en masse. The pre-scanner find the first terminating END_TAG after an opening tag, regardless of it being on a commented line or not. e.g. [%# # # [% INCLUDE blah %] <- directive ends here # foo <- this gets printed %] * Allow { and } as block delimiters, replacing for the ugly ';' and big, chunky [% END %] approach. e.g. something like: [% FOREACH a = [ 1 2 3 ] %] [% IF b == a %] [% INCLUDE foo %] [% ELSE %] [% INCLUDE bar %] [% END %] [% END %] could be written as: [% FOREACH a = [ 1 2 3 ] { IF b == a { INCLUDE foo } ELSE { INCLUDE bar } } %] * Ability to set different parser options for BLOCK definitions, etc. [% BLOCK header eval_perl = 0 pre_chomp = 1 %] ... [% END %] Anonymous BLOCK can then be used to set a parser scope [% BLOCK trim=1 %] ... [% END %] [% BLOCK trim=0 %] ... [% END %] And/or set different tag styles, etc. [% BLOCK tags='star' %] [* INCLUDE this_is_a_directive *] [% INCLUDE this_is_not %] [* END *] [% INCLUDE back_to_normal %] This is likely to be a TT3 feature and I've already got the basic parser for this up and running. It might get back-pactched into version 2, otherwise you might have to wait for the first alpha release of verion 3. * Craig Barratt reports the following: I looked at Parse.yp to see how hard it would be to push FILTER evaluation down into the expr rule, so that you could put filters inside expressions (eg: using repeat() just like "x" in perl). More about that later. In browsing through Parser.yp I noticed several issues: - The operator precedence is very different to perl, C etc. For example, these expressions evaluate differently in TT2 versus perl, C etc: + "1 || 0 && 0" evaluates to 0 in TT2 and 1 in perl or C. TT2 parses it as (1||0) && 0; in perl and C && is higher precedence than ||. + "1 + !0 + 1" evaluates to 1 in TT2 and 3 in perl or C. TT2 parses it as 1 + !(0 + 1); in perl and C ! is higher precedence than +. + Many other expressions parse incorrectly, but the effect is benign since most rules return flat text that perl correctly re-parses. Eg, 2 * 3 + 4 is incorrectly parsed as (2 * (3 + 4)), but happily just the string "2 * 3 + 4" is compiled by perl, which correctly evaluates it as (2 * 3) + 4. - There is no unary minus and the NUMBER token is signed. So you can write "x = -2;" but not "x = -y;". Moreover, "x = 1 -1;" is a syntax error (since "1 -1" returns just two tokens NUMBER, NUMBER). (As a workaround you can rewrite these as "x = 0-y;" and "x = 1 - 1".) - You cannot have expressions in lists ([..]) and function arguments. I have modified the Parser.pm (to make NUMBER unsigned) and modified Grammar.pm.skel and Parser.yp to fix most of these issues (improved operator precedence, unary minus and plus), and also to allow expressions in a few more places (eg: range). But the last item has me stuck. The parse rules for lists and function arguments make COMMA optional, so you can equivalently write [1 2 3 4] or [1,,,,,2 3 4] or [1,2,3,4]. This makes it very difficult to make each term an expression, because the resulting grammar has many ambiguities. For example, is [1 -1] two elements [1, -1] or a single element [0]? One partial solution is to move the bracketed expression rule '(' expr ')' to the term rule, allowing expressions to be included via parens. But there are also ambiguities, eg: does [foo (1+1)] have 2 elements or is it a function call to foo? Without allowing expressions in lists or function arguments, the unary minus change I've made means that the NUMBER token is unsigned, so with my changes you cannot write [-1, 2, 3]. Not a good thing. One solution is to change the grammar so that COMMAs are required in lists and arguments, but that would break several test cases and probably break lots of old templates. But this might be the only way to produce a grammar that is a lot more similar to perl. Another solution is to ignore these issues altogether and use temporary variables to precompute expressions that you need in lists or function arguments, or use explicit lvalue assignments, eg: foo(x + 2); becomes temp = x + 2; foo(temp); or List = [x+1,x+2,x+4]; becomes List = []; List.0 = x+1; List.1 = x+2; List.2 = x+4; Both of these look ugly to me. Back to the FILTER issues. Ultimately I'd like to be able to embed filters as low precedence operators in expressions, and write: List = [ "foo" | repeat(10), "bar" | repeat(10) ]; but I doubt there is a non-ambiguous upward compatible grammar that supports this. Comments? #------------------------------------------------------------------------ # Plugins #------------------------------------------------------------------------ * We need a way to easily enable/disable certain plugins. This should be addressed by facility provision. Probably something for v3. * The Text::Autoformat module has some problems with versions of Perl prior to 5.6.0 when using a locale which has a decimal separator other than '.' (e.g. Swedish, which uses ','). Damian has been made aware of the problem (and I note he now has a new version out which I need to check). For now, the Makefile.PL issues a warning but continues regardless. * The Template::Plugin DBI iterator first/last() methods don't behave the same as list first/last(). Randal also reports that get_all() doesn't work as it should - may be a conflict in code/docs? * PLUGINS could accept a reference to an object which is used as a singleton factory for a plugin. (NOTE: 2.01 includes PLUGIN_FACTORY to implement this, but currently undocumented because it's likely to change). * Add Leo & Leon's Page plugin, or try to find some way of implementing it in terms of the Table plugin. I think the jury is still out on the matter of whether it counts as duplicated functionality. * A more general solution for XML (e.g. DOM, XPath, etc) would be for TT to support a PerlSAX handler which generates the appropriate callbacks to the view. This should make it possible to easily display XML content from XML::DOM, XML::XPath, or any other SAX compliant source. Something like this: # define a view [% VIEW my_view prefix="my/xml/dom/path/" ; END %] # get some XML [% USE dom = XML.DOM %] [% doc = dom.parser(my.files.xmldata) %] # ask the view to print the data [% my_view.print(doc) %] The view print() method will call the relevant 2SAX method on the XML node, passing a SAX2TTView handler to make the relevant calls back to the view to display parts of the XML data model as SAX events are received. #------------------------------------------------------------------------ # Views #------------------------------------------------------------------------ The current implementation is there to get me (and anybody else who's interested) using it and trying to identify the problems, requirements and general issues involved. I've got a better idea now about what a VIEW should be in notional terms, but I'm still not quite sure about the syntax and API. General thoughts: * A view defines a set of templates. Things like prefix, suffix, default, etc., can be specified to customise template selection. In this sense, it is like a custom provider of those templates. It implements the template() method to fetch a template according to those rules. * It is also a custom processor of those templates. It implements the process() method. In this sense, it is like a custom context. * It also implements dispatch logic to apply the right template to the right kind of data. It does this via the print() method. It may have all kinds of custom dispatch logic. * A view takes responsiblity for things template related as opposed to anything data related (stash) or application logic related (plugins, runtime code, etc). It is the user interface facility within the engine. #------------------------------------------------------------------------ # Splash! #------------------------------------------------------------------------ The current implementation is a fairly ugly hack to get something up and running that's good enough to use. It's mainly template driven and doesn't scale very well, particularly with global variables clashing all over the place. My plan is that this will become a view-based system and will no doubt be a test-bed for the implementation of the view facility. To include: * Variable management for storing metadata relating to an interface/view, protected from the rest of template space. * Also, style management for defining different styles (e.g. plain, fancy, icecold, whitehot) for different interface elements (e.g. bars, borders, menu text) in different modes (e.g. selected, unselected), or under different, possibly custom conditions (e.g. user preferences, guest or logged in, etc.). * Clearly define API for different elements, allowing people to write apps to the API which run across different conformant widget sets. * support themes which define a set of styles * May be wise to move Splash out to a separate distribution. Randal Schwartz highlighted some problems with non-compliant HTML being generated. These include: * no DOCTYPE declaration (added to html/header) * ALT attribute missing from many <img> tags * <font ...><table>...</table></font> is illegal (not sure where this gets done) * <tr> shouldn't have HEIGHT attribute * <H3> block element inside inline element * <A> not allowed here (not sure) #------------------------------------------------------------------------ # Test Suite #------------------------------------------------------------------------ * t/file.t and t/directry.t are currently disable on Win32 until I get a chance to fix a couple of minor bugs relating to '/' vs '\' file separators. #------------------------------------------------------------------------ # Facilities #------------------------------------------------------------------------ Core facilities currently implemented by Template::Context should be moved out into separate facilities. These currently fall into the categories of things like stash, view, plugins, filters, parser and maybe some others. (NOTE: this might tie in very closely with Camelot and the resource/presenter/actor breakdown, aka model/view/controller). * 'view' would handle template fetching and processing. It is the view that talks to a provider, possibly adding special prefixes, suffixes, doing default templates, special dispatch logic, etc. * 'stash' is responsible for storing variables, as it currently is. * 'plugins' is responsible for fetching plugins. * 'filters' is responsible for fetching filters. * maybe both the above would get bundled into something like 'logic'? * 'parser' would make parts of the parser accessible * 'output' could be used to generate output There would be some facility to install, customise and remove facilities to modify TT behaviour as required. This would allow us to disable certain plugins, or remove the plugin facility altogether, for example. Or we could install a new stash facility which generated a different kind of code (e.g. less magic, more speed). Or install a new custom facility to do some application or domain specific task. Facilities should be accessible via the context: my $stash = $context->stash(); # currently works my $view = $context->view(); # not yet General form: my $xyz = $context->facility('xyz'); Multiple form: my ($a, $b, $c) = $context->facility(qw[ a b c ]); This can then be written into generated code pretty much as the stash currently is. The facilities would define the code generators that currently clutter up Template::Directives. They would ensure that the facility is scheduled to be requested from the context at the start of the sub: sub { my $context = shift; my ($stash, $view) = $context->faciity(qw( stash view )); and then transform the various directives into appropriate callbacks into the facility: $output .= $stash->get('x'); $output .= $view->process('header'); The context becomes a switching centre for the Template Toolkit, with most, if not all of its existing functionality moved out to facilities. The context should acquire all facilities at the start of a process lifecycle, run the template, and then release them all again. This should all be done according to the process contract which specifies which facilities should be installed, which can be modified, what can and can't be be loaded, and so on. The contract would also define things like PRE_PROCESS templates, error handling, etc. Thus the role of Template::Service is to undertake a contract with the client and attempt to fulfill it. A Template::Contract defines the terms of the contract and the Template::Context becomes an embodiment (runtime instance) of a contract. The current context would be available as the 'tt2' template variable, with facilities available as object methods. Thus, the following become possible: [% tt2.stash.get('foo') %] # [% foo %] [% tt2.view.process('header') %] # [% PROCESS header %] [% tt2.parser.start_tag %] # can't do this currently Directives would be re-written into code like that above. You can use the 'tt2.facility.whatever' form when directive syntax would otherwise get in the way: [% mycode( header = tt2.view.process('my/fancy/header'), footer = tt2.view.process('your/dull/footer') ) %] Or to explicitly disambiguate: [% tt2.stash.get('foo.size') %] # object method [% tt2.stash.list.size(foo) %] # virtual method [% foo.size %] # lucky dip :-) Facility management would itself be a facility. Thus, to disable runtime facility loading, you would simply unload (or not load) the facility management facility. [% tt2.facility.install(module='my_facility', name='foo') %] [% tt2.foo.bar(123) %] Note that there are some issues relating to cross-cutting facilities, otherwise known as "aspects" (see Aspect Oriented Programming). For example, variable localisation cross cuts views and data management (i.e. tt2.view.include('header', title='my title') must first localise the stash and delocalise it again afterwards). It may be appropriate to install aspects as separate entities (e.g. 'localisation') which can be invoked to apply cross cutting concerns in a generic way. Perhaps aspects are implemented as their own facility? [% tt2.aspect.localise %] ... [% tt2.aspect.delocalise %] or [% aspect = tt2.aspect.localise %] # cloned & specialised context [% aspect.view.process('header', title='my title') %] or ... Another example would be debugging: [% tt2dbg = tt2.aspect.debug(...params...) %] [% tt2dbg.view.process('header') %] or: [% tt2 = tt2.aspect.debug(...) %] ... [% tt2 = tt2.release %] #------------------------------------------------------------------------ # Output #------------------------------------------------------------------------ It should be possible to stack output buffers. In other words, you stop writing to the current output buffer and open a new buffer and start writing to that. The final output is simply the concatenation of all output buffers. The clever part of all this is that is should be possible to keep a handle on an earlier buffer and go back and append to it at some point in the future. A typical use is for generating tables of contents at the start of a document when you don't know in advance what the document contains. Simply push a new output buffer at the point of the TOC, generate the rest of the document (keeping track of all the section titles, etc) and at the end of the document, go back and generate the TOC onto the end of the first buffer. Haven't decided on any syntax yet, but it will almost certainly be implemented as a facility. At the lowest level, something like this perhaps: [% INCLUDE header %] # write content to first buffer [% toc = tt2.output.push %] # save current buffer as toc Blah blah blah # write content to second buffer [% INCLUDE footer %] [% tt2.output.buffer = toc %] # re-instate first buffer This is the TOC # append to first buffer The output stack would look something like this: +-----------------+ | <header> | | This is the TOC | +-----------------+ | V +-----------------+ | Blah blah blah | | <footer> | +-----------------+ Which to the end user, would silently be concatenated into: <header> This is the TOC Blah blah blah <footer> Another use is to ensure dependencies on other templates get resolved. For example, many of the PostScript library templates rely on other templates. At present, each template sets a global variable to say "I've been loaded" while also inspecting these variables for any templates that it relies on, loading them via INCLUDE/PROCESS if not set. e.g. ps/cross: [% # this works, but it's a bit clunky DEFAULT radius = '5 mm'; PROCESS ps/mm UNLESS global.ps.loaded.mm; global.ps.loaded.cross = 1; -%] /cross { ... } Better would be to have each template simply activate the flags for those templates that it relies on. The header file pushes a new output buffer and the footer file goes back to the header buffer and INCLUDEs the dependant templates. [% PROCESS ps/header + ps/complex %] 10 mm 10 mm complex [% PROCESS ps/footer %] ps/complex: [% global.ps.require.simple = 1 %] /complex { ... simple ... } ps/simple: [% global.ps.require.mm = 1 %] /simple { ... 31 mm 41 mm moveto ... } ps/header: %%!PS-Adobe-3.0 ... %%EndComments [% global.ps.header = tt2.output.push %] ps/footer: [% FOREACH file = ['mm','simple',...]; INCLUDE $file IF global.ps.require.$file; END; %] Ultimately, the whole ps library would become a facility. The acquire() method (called by the Template::Service to acquire the facility at the start of processing a template) would do the 'header' part (i.e. push the output buffer), and the release() method (called at the tail end to release the facility) would do the dependency checks. The dependency registrations would be facility features, e.g. gs/complex: [% tt2.ps.require.mm = 1 %] # either [% tt2.ps.require('mm', 'simple') %] # or