bpo-40334: Improvements to error-handling code in the PEG parser

[lysnikolaou]

Following improvements are implemented in this PR:

• p->error_indicator is set, in case malloc or realloc fail
• Avoid memory leaks in the case that realloc fails
• Call PyErr_NoMemory() instead of PyErr_Format(), because it
  requires no memory

https://bugs.python.org/issue40334

[lysnikolaou]

Note to self: This partially conflicts with #19987, so will probably need to merge master after that's landed.

[pablogsal]

• p->error_indicator is set, in case malloc or realloc fail

Do we need to do this? As soon as the rule returns it will go immediately to a if (_res == NULL && PyErr_Occurred()) block, no?

[lysnikolaou]

• p->error_indicator is set, in case malloc or realloc fail

Do we need to do this? As soon as the rule returns it will go immediately to a if (_res == NULL && PyErr_Occurred()) block, no?

I can't really see this, how exactly is this?

[pablogsal]

I can't really see this, how exactly is this?

I have checked again and this only happens when the rule does not return NULL, so forget what I said :(

[lysnikolaou]

Resolved the conflicts so that we can hopefully merge this and close bpo-40334.

[pablogsal]

@lysnikolaou You need to regenerate the parser 😉

[lysnikolaou]

@lysnikolaou You need to regenerate the parser 😉

Done! Sorry, it's getting late..

[pablogsal]

Done! Sorry, it's getting late..

No problem. I want to land this and the other PR so they both make it to beta 1 which is next Monday :)