compiletest seems to be generating its own macro backtrace diagnostics?

[jieyouxu]

What on earth is going on here

rust/src/tools/compiletest/src/json.rs

Lines 305 to 321 in 096277e

	fn push_backtrace(
	expected_errors: &mut Vec<Error>,
	expansion: &DiagnosticSpanMacroExpansion,
	file_name: &str,
	) {
	if Path::new(&expansion.span.file_name) == Path::new(&file_name) {
	expected_errors.push(Error {
	line_num: expansion.span.line_start,
	kind: Some(ErrorKind::Note),
	msg: format!("in this expansion of {}", expansion.macro_decl_name),
	});
	}
	if let Some(previous_expansion) = &expansion.span.expansion {
	push_backtrace(expected_errors, previous_expansion, file_name);
	}
	}

@BoxyUwU found out that compiletest seemingly emits diagnostics that are not in rustc's diagnostics. Like

error[E0425]: cannot find value `ident` in this scope
  --> $DIR/const_arg_trivial_macro_expansion-1.rs:11:9
   |
LL |         ident
   |         ^^^^^ not found in this scope
...
LL |     fn array_0() -> [(); unbraced_unbraced_ident!()] { loop {} }
   |                          -------------------------- in this macro invocation
   |
   = note: this error originates in the macro `unbraced_ident` which comes from the expansion of the macro `unbraced_unbraced_ident` (in Nightly builds, run with -Z macro-backtrace for more info)

like, compiletest is generating its own macro backtrace diagnostics or something funny like that?

[jieyouxu]

(I bet this is very load-bearing and is relied upon by many thousands of tests)