Fix never-type rvalue ICE
This fixes#43061.
r? @nikomatsakis
A small post-mortem as a follow-up to our investigations in https://github.com/rust-lang/rust/pull/47291:
The problem as I understand it is that when `NeverToAny` coercions are made, the expression/statement that is coerced may be enclosed in a block. In our case, the statement `x;` was being transformed to something like: `NeverToAny( {x;} )`. Then, `NeverToAny` is transformed into an expression:
000fbbc9b8/src/librustc_mir/build/expr/into.rs (L52-L59)
Which ends up calling `ast_block_stmts` on the block `{x;}`, which triggers this condition:
000fbbc9b8/src/librustc_mir/build/block.rs (L141-L147)
In our case, there is no return expression, so `push_assign_unit` is called. But the block has already been recorded as _diverging_, meaning the result of the block will be assigned to a location of type `!`, rather than `()`. This causes the MIR error.
I'm assuming the `NeverToAny` coercion code is doing what it's supposed to (there don't seem to be any other problems), so fixing the issue simply consists of checking that the destination for the return value actually _is_ supposed to be a unit. (If no return value is given, the only other possible type for the return value is `!`, which can just be ignored, as it will be unreachable anyway.)
I checked the other cases of `push_assign_unit`, and it didn't look like they could be affected by the divergence issue (blocks are kind of special-cased in this regard as far as I can tell), so this should be sufficient to fix the issue.
Libtest json output
A revisit to my [last PR](https://github.com/rust-lang/rust/pull/45923).
Events are now more atomic, printed in a flat hierarchy.
For the normal test output:
```
running 1 test
test f ... FAILED
failures:
---- f stdout ----
thread 'f' panicked at 'assertion failed: `(left == right)`
left: `3`,
right: `4`', f.rs:3:1
note: Run with `RUST_BACKTRACE=1` for a backtrace.
failures:
f
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
```
The JSON equivalent is:
```
{ "type": "suite", "event": "started", "test_count": "1" }
{ "type": "test", "event": "started", "name": "f" }
{ "type": "test", "event": "failed", "name": "f" }
{ "type": "suite", "event": "failed", "passed": 0, "failed": 1, "allowed_fail": 0, "ignored": 0, "measured": 0, "filtered_out": "0" }
{ "type": "test_output", "name": "f", "output": "thread 'f' panicked at 'assertion failed: `(left == right)`
left: `3`,
right: `4`', f.rs:3:1
note: Run with `RUST_BACKTRACE=1` for a backtrace.
" }
```
For E0277 on `for` loops, point at the "head" expression
When E0277's span points at a `for` loop, the actual issue is in the
element being iterated. Instead of pointing at the entire loop, point
only at the first line (when possible) so that the span ends in the
element for which E0277 was triggered.
Match libunwind's EABI selection with libpanic_unwind
Currently, the `libunwind` crate will only select the ARM EABI if it is compiling for ARM/Linux or Android targets. `libpanic_unwind`, however, will choose the ARM EABI if the target arch is ARM and the OS is not iOS. This means that if one tries to enable unwinding for a non-standard ARM target (such as implementing a custom stdlib via Xargo, for example), then the two crates can potentially disagree about which EABI is being targeted.
This PR makes `libunwind` use the [same logic](https://github.com/rust-lang/rust/blob/master/src/libpanic_unwind/gcc.rs#L139-L146) as `libpanic_unwind` when choosing the EABI.
I noticed there are a few comments about certain functions only differing on Android or ARM/Linux, but I *think* that those differences apply to the ARM EABI in general. Let me know if I'm wrong about that.
libtest: Split HumanFormatter into {Pretty,Terse}
libtest: Fixed padding of benchmarks when not benchmarking
libtest: Fixed benchmarks' names not showing in terse-mode
libtest: Formatting
libtest: Json format now outputs failed tests' stdouts.
libtest: Json format now outputs failed tests' stdouts.
libtest: Json formatter now spews individiual events, not as an array
libtest: JSON fixes
libtest: Better JSON escaping
libtest: Test start event is printed on time
We can't use git commands to compute a prerelease version when we're
building from a source tarball, or if git is otherwise unavailable.
We'll just call such builds `x.y.z-beta`, without a prerelease.
