Check start tags were matched to an end tag

[paulharris]

Template:

{#username}
{^username}

Context:
{ "username": "" }

The problem appears to be in ActionType::ElseBlock, which find the context, but doesn't have a switch case for json::type::String, and instead sets current=action.pos

Crow/include/crow/mustache.h

Line 349 in 25ca2f5

current = action.pos;

For this template, there are 2 actions.
At this point we are on the second action (current=1)
But this action's "pos" is = 0.
So, current is reset to zero, and it loops through again and again, never progressing.

This seems related to #899
I think the problem is pos is never set to a valid point... this is done in case'/', ie when the parser sees the end tag.
But, if there is never an end-tag, it never checks if there are unmatched pairs, and pos is never set.

So, I've adjusted the code so it always expects a non-negative pos.
pos is initialised by default to -1 for start tags.
And end tag will match it and set it to a valid pos.

For all other normal tags, it is initialised to zero.

THIS was a quick first-pass patch, as I'm not familiar with mustache, so I imagine this patch is NOT COMPLETE.
It needs to be run through a test suite.

[gittiver]

Are there already tests for this cases?

[gittiver]

actually some tests fail

[paulharris]

Sorry about that, I didn't check the tests.
I've forced-pushed, start again...
I've fixed some unsigned/signed warnings (be consistent if using static_cast() ... in C++20 can switch to std::ssize()).
I've added a test for the mustache - in a new JSON test as I assume the existing json files are from the mustache spec test dataset?
I've adjusted my method for detecting missing end tags, improved the error message, and it now works.

You can see the infinite loop by checking out this branch, but wind back one commit to before the fix.

[paulharris]

I've been using my fix with success, just need a review to push this through.