Perform `cfg` attribute processing during macro expansion and fix bugs
This PR refactors `cfg` attribute processing and fixes bugs. More specifically:
- It merges gated feature checking for stmt/expr attributes, `cfg_attr` processing, and `cfg` processing into a single fold.
- This allows feature gated `cfg` variables to be used in `cfg_attr` on unconfigured items. All other feature gated attributes can already be used on unconfigured items.
- It performs `cfg` attribute processing during macro expansion instead of after expansion so that macro-expanded items are configured the same as ordinary items. In particular, to match their non-expanded counterparts,
- macro-expanded unconfigured macro invocations are no longer expanded,
- macro-expanded unconfigured macro definitions are no longer usable, and
- feature gated `cfg` variables on macro-expanded macro definitions/invocations are now errors.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m {
() => {
#[cfg(attr)]
macro_rules! foo { () => {} }
foo!(); // This will be an error
macro_rules! bar { () => { fn f() {} } }
#[cfg(attr)] bar!(); // This will no longer be expanded ...
fn g() { f(); } // ... so that `f` will be unresolved.
#[cfg(target_thread_local)] // This will be a gated feature error
macro_rules! baz { () => {} }
}
}
m!();
```
r? @nrc
Fix misleading intentation errors on gcc 6.0
Currently building with latest gcc results in the following error:
compile: x86_64-unknown-linux-gnu/rt/miniz.o
/home/lc/rust/src/rt/miniz.c: In function ‘tinfl_decompress’:
/home/lc/rust/src/rt/miniz.c:578:9: error: this ‘for’ clause does not guard... [-Werror=misleading-indentation]
for ( i = 0; i <= 143; ++i) *p++ = 8; for ( ; i <= 255; ++i) *p++ = 9; for ( ; i <= 279; ++i) *p++ = 7; for ( ; i <= 287; ++i) *p++ = 8;
^~~
/home/lc/rust/src/rt/miniz.c:578:47: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘for’
for ( i = 0; i <= 143; ++i) *p++ = 8; for ( ; i <= 255; ++i) *p++ = 9; for ( ; i <= 279; ++i) *p++ = 7; for ( ; i <= 287; ++i) *p++ = 8;
^~~
/home/lc/rust/src/rt/miniz.c: In function ‘tdefl_find_match’:
/home/lc/rust/src/rt/miniz.c:1396:5: error: this ‘if’ clause does not guard... [-Werror=misleading-indentation]
if (!dist) break; p = s; q = d->m_dict + probe_pos; for (probe_len = 0; probe_len < max_match_len; probe_len++) if (*p++ != *q++) break;
^~
/home/lc/rust/src/rt/miniz.c:1396:23: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘if’
if (!dist) break; p = s; q = d->m_dict + probe_pos; for (probe_len = 0; probe_len < max_match_len; probe_len++) if (*p++ != *q++) break;
^
This patch stops this.
Add `make tips` as useful make target
By accident, I found the `make tips` target, which helped me to gain more insight on how to work with the system more quickly.
Trait documentation clarifications
Hi! I've felt a bit of friction lately in figuring out how to write custom implementations of the `derive`able traits, so I decided to add to the docs :)
The docs for `Copy` are already excellent-- clear, useful sections that I only reordered a bit-- they're now:
* General explanation
* When can my type be `Copy`?
* When can my type _not_ be `Copy`?
* When should my type be `Copy`?
* Derivable
* How can I implement `Copy`?
I didn't add all these sections for all the traits, but I did make sure all the derivable traits had a consistent "Derivable" section that explained what the derived implementation does and a "How can I implement" section that has an example.
Please check me for correctness-- I tried to do research to make sure I was saying accurate things but I'm still learning! ❤️ I'd also love suggestions on information to add that is still missing-- I think these traits are important and deserve to have awesome docs!
Fix `asm-misplaced-option` on ARM/AArch64
This fixesrust-lang/rust#33737. Of course, since we don't run `make check` for ARM cross builds, you probably won't notice it.
This makes the \"shadowing labels\" warning *not* print the entire loop as a span, but only the lifetime.
Also makes #31719 go away, but does not fix its root cause (the span of the expanded loop is still wonky, but not used anymore).
Fix handling of FFI arguments
r? @eddyb @nikomatsakis or whoever else.
cc @alexcrichton @rust-lang/core
The strategy employed here was to essentially change code we generate from
```llvm
%s = alloca %S ; potentially smaller than argument, but never larger
%1 = bitcast %S* %s to { i64, i64 }*
store { i64, i64 } %0, { i64, i64 }* %1, align 4
```
to
```llvm
%1 = alloca { i64, i64 } ; the copy of argument itself
store { i64, i64 } %0, { i64, i64 }* %1, align 4
%s = bitcast { i64, i64 }* %1 to %S* ; potentially truncate by casting to a pointer of smaller type.
```
