ui test suite fails on stage 1

[RalfJung]

With current master (81cfaad), the UI stage 1 test suite fails for me. ./x.py --stage 1 test src/test/ui --bless introduces the following diff:

--- a/src/test/ui/macros/macros-nonfatal-errors.stderr
+++ b/src/test/ui/macros/macros-nonfatal-errors.stderr
@@ -1,4 +1,4 @@
-error[E0665]: `Default` cannot be derived for enums, only structs
+error: `Default` cannot be derived for enums, only structs
   --> $DIR/macros-nonfatal-errors.rs:20:10
    |
 LL | #[derive(Default)] //~ ERROR
@@ -96,5 +96,4 @@ LL |     trace_macros!(invalid); //~ ERROR
 
 error: aborting due to 15 previous errors
 
-Some errors occurred: E0658, E0665.
-For more information about an error, try `rustc --explain E0658`.
+For more information about this error, try `rustc --explain E0658`.

Stage 1 used to work fine, so this is a regression, likely introduced by #53196 (cc @davidtwco).

Stage 2 build is still running.

[varkor]

Fixed by #53368.

[RalfJung]

FWIW, stage 2 works. I am surprised that such a difference is possible between stages...

[varkor]

It's explicitly gated on stage 2 (i.e. being compiled by stage 1 or greater):

rust/src/libsyntax_ext/deriving/default.rs

Lines 78 to 80 in bc8cead

	StaticEnum(..) => {
	span_err_if_not_stage0!(cx, trait_span, E0665,
	"`Default` cannot be derived for enums, only structs");

I'm not quite sure why the only difference is emitting the error code or not, though:

rust/src/libsyntax_ext/deriving/mod.rs

Lines 22 to 31 in bc8cead

	macro_rules! span_err_if_not_stage0 {
	($cx:expr, $sp:expr, $code:ident, $text:tt) => {
	#[cfg(not(stage0))] {
	span_err!($cx, $sp, $code, $text)
	}
	#[cfg(stage0)] {
	$cx.span_err($sp, $text)
	}
	}
	}

[davidtwco]

Huh, that's interesting. I was always testing against stage 2 locally when working on #53196 and Travis didn't seem to pick that up either.

[varkor]

Fixed by #53368 (comment).