Nunjucks-slim fails on installJinjaCompat()

[krassowski]

Hi, many thanks for releasing the 3.0.1 version. I am trying to use the slice syntax with nunjucks-slim. I got help with pre-compilation in Jinja Compatibility mode, but I cannot use the pre-compiled tempates. It seems that there is a bug in installJinjaCompat() for nunjucks-slim; the bug:

nunjucks-slim.js:2910 Uncaught TypeError: Cannot read property 'prototype' of undefined
    at Object.installCompat [as installJinjaCompat] (nunjucks-slim.js:2910)
    at window.onload ((index):45)
installCompat @ nunjucks-slim.js:2910
window.onload @ (index):45

Following code is sufficient to reproduce:

<script src="https://cdnjs.cloudflare.com/ajax/libs/nunjucks/3.0.1/nunjucks-slim.js"></script>
<script>
nunjucks.installJinjaCompat();
</script>

And here is jsfiddle with some additional testing code.

Is it a bug, or an intended behaviour? How can I make Jinja compatibility mode work with nunjucks-slim?

[noahlange]

My guess is that jinja-compat is attempting to patch both the runtime and the compiler/parser, and since the latter are not included in slim, it's exploding.

nunjucks/src/jinja-compat.js

Lines 14 to 15 in 6f4739e

	var orig_Compiler_assertType = Compiler.prototype.assertType;
	var orig_Parser_parseAggregate = Parser.prototype.parseAggregate;

My guess is that's where it's choking. Options include:

1. split jinja-compat into runtime and compile-time components
2. put some if/else blocks that prevent the compiler/parser patching from happening in slim

If this is still a relevant issue for y'all, I can take a look at writing a PR.

[fdintino]

Is there actually value in having a separate installJinjaCompat, rather than having it be merged in with standard functionality? It would certainly make the code simpler.

[noahlange]

Hmm. I think if we were ever to consider Liquid or Twig compatibility patches, merging the changes from Jinja2's compatibility patch into "core" might turn out to bite us.

I really like the slice operator, but many of the other changes are very Pythonic.

[fdintino]

A fix for this is in the works.