I have been using template toolkit for extending an existing domain specific language(verilog) for over 3 years now. While overall I am happy with it, the major irritant is that
I can suggest HTML::Template:Compiled (but note I'm the author ;-)
It is quite compatible to HTML::Template, but has additional features.
Support for complex data structures
yes
Good error reporting and debug capabilities.
You can debug cache hits, misses, automatically add template filename to output and can use a filter "DUMP" for the current variable in stash (or any variable). If it's easy to implement I'll happily add more useful debugging.
Stable and proven ( no alpha/beta level engines)
I would consider it stable now, with the documented limitations/bugs (for example query())
Extensible (plugin's etc)
supports escape (filter) plugins and more, though the latter is not documented very well yet.
Should not be restricted to a given language (html etc.)
yes
support for IF/Else, looping(foreach while), Loop indexing, etc.
yes
Preferably perl
yes
Support for data dumper or equivalent plugin from within the template is a plus
like mentioned above, use escape=dump
all additional features are listed in the documentation: https://metacpan.org/release/HTML-Template-Compiled at "ADDITIONAL FEATURES"
edit: regarding reporting runtime errors: unfortunately H::T::C also does not report the template line number for errors that happen at runtime, since it compiles the template to perl-code (I think I experimented with manipulating line numbers once, maybe I'll have another look). template syntax errors are reported with the correct line number.
edit2: So here's an example with the new options warnings and line_info:
t/templates/line_info1.html:
test
test2
test3
foo:<%= foo %> undef line 4
test4
script:
use HTML::Template::Compiled;
my $t = HTML::Template::Compiled->new(
filename => "t/templates/line_info1.html",
warnings => 1,
line_info => 1,
);
say $t->output;
__END__
Use of uninitialized value in concatenation (.) or string at t/templates/line_info1.html line 4.
test
test2
test3
foo: undef line 4
test4