This is theoretically a breaking change, but GitHub search turns up no
uses of it, and most non-built-in cfg's are passed via cargo features,
which look like `feature = "..."`, and hence can't overlap.
This pull request implements the functionality for [RFC 873](https://github.com/rust-lang/rfcs/blob/master/text/0873-type-macros.md). This is currently just an update of @freebroccolo's branch from January, the corresponding commits are linked in each commit message.
@nikomatsakis and I had talked about updating the macro language to support a lifetime fragment specifier, and it is possible to do that work on this branch as well. If so we can (collectively) talk about it next week during the pre-RustCamp work week.
This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.
[rfc]: https://github.com/rust-lang/rfcs/pull/1184
`LocalSource` indicated wether a let binding originated from for-loop desugaring to enable specialized error messages, but for-loop expansion has changed and this is now achieved through `MatchSource::ForLoopDesugar`.
(Over time the stability checking has gotten more finicky; in
particular one must attach the (whole) span of the original `in PLACE
BLOCK` expression to the injected references to unstable paths, as
noted in the comments.)
call `push_compiler_expansion` during the placement-`in` expansion.
Even after expansion, the generated expressions still track depth of
such pushes (i.e. how often you have "pushed" without a corresponding
"pop"), and we add a rule that in a context with a positive
`push_unsafe!` depth, it is effectively an `unsafe` block context.
(This way, we can inject code that uses `unsafe` features, but still
contains within it a sub-expression that should inherit the outer
safety checking setting, outside of the injected code.)
This is a total hack; it not only needs a feature-gate, but probably
should be feature-gated forever (if possible).
ignore-pretty in test/run-pass/pushpop-unsafe-okay.rs
This is a port of @eddyb's `const-fn` branch. I rebased it, tweaked a few things, and added tests as well as a feature gate. The set of tests is still pretty rudimentary, I'd appreciate suggestions on new tests to write. Also, a double-check that the feature-gate covers all necessary cases.
One question: currently, the feature-gate allows the *use* of const functions from stable code, just not the definition. This seems to fit our usual strategy, and implies that we might (perhaps) allow some constant functions in libstd someday, even before stabilizing const-fn, if we were willing to commit to the existence of const fns but found some details of their impl unsatisfactory.
r? @pnkfelix
- add feature gate
- add basic tests
- adjust parser to eliminate conflict between `const fn` and associated
constants
- allow `const fn` in traits/trait-impls, but forbid later in type check
- correct some merge conflicts
There were still some mentions of `~[T]` and `~T`, mostly in comments and debugging statements. I tried to do my best to preserve meaning, but I might have gotten some wrong-- I'm happy to fix anything :)
There are two interesting kinds of breakage illustrated here:
1. `Box<Trait>` in many contexts is treated as `Box<Trait + 'static>`,
due to [RFC 599]. However, in a type like `&'a Box<Trait>`, the
`Box<Trait>` type will be expanded to `Box<Trait + 'a>`, again due
to [RFC 599]. This, combined with the fix to Issue 25199, leads to
a borrowck problem due the combination of this function signature
(in src/libstd/net/parser.rs):
```rust
fn read_or<T>(&mut self, parsers: &mut [Box<FnMut(&mut Parser) -> Option<T>>]) -> Option<T>;
```
with this call site (again in src/libstd/net/parser.rs):
```rust
fn read_ip_addr(&mut self) -> Option<IpAddr> {
let ipv4_addr = |p: &mut Parser| p.read_ipv4_addr().map(|v4| IpAddr::V4(v4));
let ipv6_addr = |p: &mut Parser| p.read_ipv6_addr().map(|v6| IpAddr::V6(v6));
self.read_or(&mut [Box::new(ipv4_addr), Box::new(ipv6_addr)])
}
```
yielding borrowck errors like:
```
parser.rs:265:27: 265:69 error: borrowed value does not live long enough
parser.rs:265 self.read_or(&mut [Box::new(ipv4_addr), Box::new(ipv6_addr)])
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
(full log at: https://gist.github.com/pnkfelix/e2e80f1a71580f5d3103 )
The issue here is perhaps subtle: the `parsers` argument is
inferred to be taking a slice of boxed objects with the implicit
lifetime bound attached to the `self` parameter to `read_or`.
Meanwhile, the fix to Issue 25199 (added in a forth-coming commit)
is forcing us to assume that each boxed object may have a
destructor that could refer to state of that lifetime, and
*therefore* that inferred lifetime is required to outlive the boxed
object itself.
In this case, the relevant boxed object here is not going to make
any such references; I believe it is just an artifact of how the
expression was built that it is not assigned type:
`Box<FnMut(&mut Parser) -> Option<T> + 'static>`.
(i.e., mucking with the expression is probably one way to fix this
problem).
But the other way to fix it, adopted here, is to change the
`read_or` method type to force make the (presumably-intended)
`'static` bound explicit on the boxed `FnMut` object.
(Note: this is still just the *first* example of breakage.)
2. In `macro_rules.rs`, the `TTMacroExpander` trait defines a method
with signature:
```rust
fn expand<'cx>(&self, cx: &'cx mut ExtCtxt, ...) -> Box<MacResult+'cx>;
```
taking a `&'cx mut ExtCtxt` as an argument and returning a
`Box<MacResult'cx>`.
The fix to Issue 25199 (added in aforementioned forth-coming
commit) assumes that a value of type `Box<MacResult+'cx>` may, in
its destructor, refer to a reference of lifetime `'cx`; thus the
`'cx` lifetime is forced to outlive the returned value.
Meanwhile, within `expand.rs`, the old code was doing:
```rust
match expander.expand(fld.cx, ...).make_pat() { ... => immutable borrow of fld.cx ... }
```
The problem is that the `'cx` lifetime, inferred for the
`expander.expand` call, has now been extended so that it has to
outlive the temporary R-value returned by `expanded.expand`. But
call is also reborrowing `fld.cx` *mutably*, which means that this
reborrow must end before any immutable borrow of `fld.cx`; but
there is one of those within the match body. (Note that the
temporary R-values for the input expression to `match` all live as
long as the whole `match` expression itself (see Issue #3511 and PR
#11585).
To address this, I moved the construction of the pat value into its
own `let`-statement, so that the `Box<MacResult>` will only live
for as long as the initializing expression for the `let`-statement,
and thus allow the subsequent immutable borrow within the `match`.
[RFC 599]: https://github.com/rust-lang/rfcs/blob/master/text/0599-default-object-bound.md
Changes the style guidelines regarding unit tests to recommend using a
sub-module named "tests" instead of "test" for unit tests as "test"
might clash with imports of libtest.
* In noop_fold_expr, call new_span in these cases:
- ExprMethodCall's identifier
- ExprField's identifier
- ExprTupField's integer
Calling new_span for ExprMethodCall's identifier is necessary to print
an acceptable diagnostic for write!(&2, ""). We see this error:
<std macros>:2:20: 2:66 error: type `&mut _` does not implement any method in scope named `write_fmt`
<std macros>:2 ( & mut * $ dst ) . write_fmt ( format_args ! ( $ ( $ arg ) * ) ) )
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With this change, we also see a macro expansion backtrace leading to
the write!(&2, "") call site.
* After fully expanding a macro, we replace the expansion expression's
span with the original span. Call fld.new_span to add a backtrace to
this span. (Note that I'm call new_span after bt.pop(), so the macro
just expanded isn't on the backtrace.)
The motivating example for this change is println!("{}"). The format
string literal is concat!($fmt, "arg") and is inside the libstd macro.
We need to see the backtrace to find the println! call site.
* Add a backtrace to the format_args! format expression span.
Addresses #23459
Statement macros are now treated somewhat like item macros, in that a statement macro can now expand into a series of statements, rather than just a single statement.
This allows statement macros to be nested inside other kinds of macros and expand properly, where previously the expansion would only work when no nesting was present.
See:
- `src/test/run-pass/macro-stmt_macro_in_expr_macro.rs`
- `src/test/run-pass/macro-nested_stmt_macro.rs`
This changes the interface of the MacResult trait. make_stmt has become make_stmts and now returns a vector, rather than a single item. Plugin writers who were implementing MacResult will have breakage, as well as anyone using MacEager::stmt.
See:
- `src/libsyntax/ext/base.rs`
This also causes a minor difference in behavior to the diagnostics produced by certain malformed macros.
See:
- `src/test/compile-fail/macro-incomplete-parse.rs`
Implements pop() on SmallVector, and uses it to expand the final semicolon
in a statement macro expansion more efficiently.
Corrects the placement of the call to fld.cx.bt_pop(). It must run
unconditionally to reverse the corresponding push.
