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Luciano Federico Pereira
Luciano Federico Pereira

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Jinja2TT2: Jinja2 to Template Toolkit Transpiler

#perl #python

jinja2tt2 logo a tori and a camel

A Perl transpiler that converts Jinja2 templates to Template Toolkit 2 (TT2) syntax.

Source: https://github.com/lucianofedericopereira/jinja2tt2

Description

Jinja2 is deeply integrated with Python, making a direct port impractical. However, since TT2 and Jinja2 share similar concepts and syntax patterns, this transpiler performs a mechanical translation between the two template languages.

Why TT2?

TT2 and Jinja2 share:

  • Variable interpolation: {{ var }} maps to [% var %]
  • Control structures: {% if %} / {% for %} map to [% IF %] / [% FOREACH %]
  • Filters: {{ name|upper }} maps to [% name | upper %]
  • Includes, blocks, and inheritance (conceptually similar)
  • Expression grammar close enough to map mechanically

Installation

No external dependencies beyond core Perl 5.20+.

git clone https://github.com/lucianofedericopereira/jinja2tt2
cd jinja2tt2
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Usage

Command Line 

# Transpile a file to stdout
./bin/jinja2tt2 template.j2

# Transpile with output to file
./bin/jinja2tt2 template.j2 -o template.tt

# Transpile in-place (creates .tt file)
./bin/jinja2tt2 -i template.j2

# From stdin
echo '{{ name|upper }}' | ./bin/jinja2tt2

# Debug mode (shows tokens and AST)
./bin/jinja2tt2 --debug template.j2
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Programmatic Usage 

use Jinja2::TT2;

my $transpiler = Jinja2::TT2->new();

# From string
my $tt2 = $transpiler->transpile('{{ user.name|upper }}');
# Result: [% user.name.upper %]

# From file
my $tt2 = $transpiler->transpile_file('template.j2');
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Supported Constructs

Variables 

{{ foo }}           →  [% foo %]
{{ user.name }}     →  [% user.name %]
{{ items[0] }}      →  [% items.0 %]
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Filters 

{{ name|upper }}              →  [% name.upper %]
{{ name|lower|trim }}         →  [% name.lower.trim %]
{{ items|join(", ") }}        →  [% items.join(', ') %]
{{ name|default("Guest") }}   →  [% (name || 'Guest') %]
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Conditionals 

{% if user %}          →  [% IF user %]
{% elif admin %}       →  [% ELSIF admin %]
{% else %}             →  [% ELSE %]
{% endif %}            →  [% END %]
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Loops 

{% for item in items %}    →  [% FOREACH item IN items %]
{{ loop.index }}           →  [% loop.count %]
{{ loop.first }}           →  [% loop.first %]
{{ loop.last }}            →  [% loop.last %]
{% endfor %}               →  [% END %]
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Blocks and Macros 

{% block content %}        →  [% BLOCK content %]
{% endblock %}             →  [% END %]

{% macro btn(text) %}      →  [% MACRO btn(text) BLOCK %]
{% endmacro %}             →  [% END %]
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Comments 

{# This is a comment #}    →  [%# This is a comment %]
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Whitespace Control 

{{- name -}}               →  [%- name -%]
{%- if x -%}               →  [%- IF x -%]
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Other Constructs

  • {% include "file.html" %} → [% INCLUDE file.html %]
  • {% set x = 42 %} → [% x = 42 %]
  • Ternary: {{ x if cond else y }} → [% (cond ? x : y) %]
  • Boolean literals: true/false → 1/0

Filter Mapping

Jinja2 TT2 Equivalent
upper .upper
lower .lower
trim .trim
first .first
last .last
length .size
join .join
reverse .reverse
sort .sort
escape / e `\
{% raw %}default `\
{% raw %}replace .replace

Some filters require TT2 plugins (e.g., tojson needs Template::Plugin::JSON).

Loop Variable Mapping

Jinja2 TT2
loop.index loop.count
loop.index0 loop.index
loop.first loop.first
loop.last loop.last
loop.length loop.size

Limitations

  • Template inheritance ({% extends %}) requires manual adjustment for TT2's WRAPPER pattern
  • Autoescape is not directly supported in TT2
  • Some filters need custom TT2 plugins or vmethods
  • Complex Python expressions may need review

Running Tests 

prove -l t/
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Architecture

  1. Tokenizer: Splits Jinja2 source into tokens (text, variables, statements, comments)
  2. Parser: Builds an Abstract Syntax Tree (AST) from the token stream
  3. Emitter: Walks the AST and generates equivalent TT2 code

Credits

  • Luciano Federico Pereira - Author

License

This is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License (LGPL) version 2.1 as published by the Free Software Foundation.

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