POSIX specifies that the sa_handler field of the sigaction struct may
be set to SIG_IGN or SIG_DFL. However, the current constants in the
standard library use the function pointer signature corresponding to
the sa_sigaction field instead.
This may not cause issues in practice because the fields usually occupy
the same memory in a union, but this isn't required by POSIX and there
may be systems we do not yet support that do this differently.
Fixing this also makes the Zig interface less confusing to use after
reading the man page.
This effectively reverts 22690efcc2378222503cb8aaad26a6f4a539f5aa,
re-opening #11818.
This had the following problems:
* Buggy on some targets (macOS, Windows)
* Messy output to the terminal
These problems need to be solved before moving forward with this.
This is likely the cause of the flaky test failures in master branch.
Since we have some test coverage for incremental compilation, it's not
OK to leave proper memory management of Fn objects as "TODO".
This improves the following test case:
```zig
pub fn main() !void {
try foo();
}
fn foo() !void {
return error.Bad;
}
```
The error return trace now points to the `try` token instead of pointing
to the foo() function call, matching stage1.
Closes#12308.
Sema: insert an error return trace frame when appropriate when analyzing
ret_load. Also optimize the instructions to avoid an unnecessary block
sent to the backends.
AstGen: always emit a dbg_stmt for return expressions, in between the
defer instructions and the return instruction.
This improves the following test case:
```zig
pub fn main() !void {
return foo();
}
fn foo() !void {
return error.Bad;
}
```
The error return trace now points to the return token instead of
pointing to the foo() function call, matching stage1.
stage2 was adding bogus error return trace frames when an error was not
being returned. This commit makes several improvements:
* Make a runtime check if necessary to only emit a frame into the error
return trace when an actual error is returned.
* Use the `analyzeIsNonErrComptimeOnly` machinery to avoid runtime
checks when it is compile-time-known that the value is an error, or a
non-error.
* Make std.builtin.returnError take a non-optional stack trace pointer.
closes#12174
