Trans has been assuming that tag node id's are unique across crates and they
are not so, depending on which way the wind is blowing, it would choose to use
a crate-local tag variant instead of the correct one from std.
No test case since I can't come up with a reliable one that compiles in a
reasonable amount of time.
also repair various errors in the parser related to such blocks.
rename checked_blk to default_blk to reflect the fact that it
inherits its purity from the surrounding context.
Upvars are now marked with def_upvar throughout, not just when going
through freevars::lookup_def. This makes things less error-prone. One
thing to watch out for is that def_upvar is used in `for each` bodies
too, when they refer to a local outside the body.
Having it in the alias pass was slightly more efficient (finding
expression roots has to be done in both passes), but further muddled
up the already complex alias checker.
Also factors out some duplication in the mutability-checking code.
This patch supports the syntax
unchecked {
...
}
to disable purity checking within a block. Presumably it will only be
used within a declared "pure fn". However, there is no checking that it
doesn't occur elsewhere, and it would be harmless for it to do so.
I went with Lindsey's suggestion for the syntax, but it's subject to
change.
This allows you to write code that uses predicates that call arbitrary
Rust functions, but you must declare your intentions by wrapping it in
an unchecked { ... } block. The test case run-pass/unchecked-predicates.rs
demonstrates how to do that.
