This makes it possible to omit the semicolon after the block, and will
cause the pretty-printer to properly print such calls (if
pretty-printing of blocks wasn't so broken). Block calls (with the
block outside of the parentheses) can now only occur at statement
level, and their value can not be used. When calling a block-style
function that returns a useful value, the block must be put insde the
parentheses.
Issue #1054
We were only using it in a single place, and there for no discernable reason
(probably as part of the bare-fn-vals-are-not-copyable plan). It seems more
surprising than useful.
Arguments that can't be safely referenced will be implicitly copied.
(Warnings for expensive copies will be forthcoming.)
This will allow us to get rid of most of the ampersands in function
signatures. See [1].
[1] https://mail.mozilla.org/pipermail/rust-dev/2011-September/000759.html
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.
