[WIP] middle/check_const: CheckItemRecursion should only recurse into NodeItems

[bgamari]

This fixes a bug in libsyntax which would crash on ASTs containing references to foreign externs. Previously the included test would fail with,

rustc' failed at 'expected item, found foreign item test_extern::test_extern (id=13)', /opt/exp/rust/src/libsyntax/ast_map.rs:264

[alexcrichton]

Did you mean to close this? If you force-push then everything will be auto-updated.

Also, is there an associated issue for this? If you put Closes #XXXX then it'll be automatically closed by github when this is merged to master.

[bgamari]

There isn't an issue. I stumbled upon this while working and fixed it after speaking with eddyb.

I closed it as the patch doesn't fix the issue completely (the test fails which I attributed to a quirk in my local configuration, I opened this pull request to see if the failure was reproducible on the CI box)

[alexcrichton]

Ah ok, I'm reopening so we can keep tabs on this, you can just force-push your branch to get github to update it.

[bgamari]

I'm now back from travel. I'll probably have a chance to look at this again over the weekend but if anyone has any ideas about my comment above, they can only help.