De-weirdify fatally_break_rust.

The easter egg ICE on `break rust` is weird: it's the one ICE in the
entire compiler that doesn't immediately abort, which makes it
annoyingly inconsistent.

This commit changes it to abort. As part of this, the extra notes are
now appended onto the bug dignostic, rather than being printed as
individual note diagnostics, which changes the output format a bit.
These changes don't interferes with the joke, but they do help with my
ongoing cleanups to error handling.

Author: nnethercote

compiler/rustc_hir_typeck/src/lib.rs

@@ -52,7 +52,7 @@ use crate::expectation::Expectation;
 use crate::fn_ctxt::RawTy;
 use crate::gather_locals::GatherLocalsVisitor;
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::{struct_span_err, Diagnostic, DiagnosticId, ErrorGuaranteed, Level};
+use rustc_errors::{struct_span_err, DiagnosticId, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::Visitor;
@@ -412,26 +412,23 @@ enum TupleArgumentsFlag {
     TupleArguments,
 }
 
-fn fatally_break_rust(tcx: TyCtxt<'_>) {
+fn fatally_break_rust(tcx: TyCtxt<'_>) -> ! {
     let handler = tcx.sess.diagnostic();
-    // We normally use `handler.bug()` for bugs, but this is an exceptional case, so we do this
-    // instead to avoid an abort.
-    handler.emit_diagnostic(Diagnostic::new(
-        Level::Bug,
-        "It looks like you're trying to break rust; would you like some ICE?",
-    ));
-    handler.note("the compiler expectedly panicked. this is a feature.");
-    handler.note(
+    let mut diag =
+        handler.struct_bug("It looks like you're trying to break rust; would you like some ICE?");
+    diag.note("the compiler expectedly panicked. this is a feature.");
+    diag.note(
         "we would appreciate a joke overview: \
          https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675",
     );
-    handler.note(format!("rustc {} running on {}", tcx.sess.cfg_version, config::host_triple(),));
+    diag.note(format!("rustc {} running on {}", tcx.sess.cfg_version, config::host_triple(),));
     if let Some((flags, excluded_cargo_defaults)) = rustc_session::utils::extra_compiler_flags() {
-        handler.note(format!("compiler flags: {}", flags.join(" ")));
+        diag.note(format!("compiler flags: {}", flags.join(" ")));
         if excluded_cargo_defaults {
-            handler.note("some of the compiler flags provided by cargo are hidden");
+            diag.note("some of the compiler flags provided by cargo are hidden");
         }
     }
+    diag.emit();
 }
 
 /// `expected` here is the expected number of explicit generic arguments on the trait.

tests/ui/track-diagnostics/track.stderr

@@ -13,14 +13,11 @@ LL |     break rust
 -Ztrack-diagnostics: created at compiler/rustc_passes/src/loops.rs:LL:CC
 
 error: internal compiler error: It looks like you're trying to break rust; would you like some ICE?
-
-note: the compiler expectedly panicked. this is a feature.
-
-note: we would appreciate a joke overview: https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675
-
-note: rustc $VERSION running on $TARGET
-
-note: compiler flags: ... -Z ui-testing ... -Z track-diagnostics
+   |
+   = note: the compiler expectedly panicked. this is a feature.
+   = note: we would appreciate a joke overview: https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675
+   = note: rustc $VERSION running on $TARGET
+   = note: compiler flags: ... -Z ui-testing ... -Z track-diagnostics
 
 error: aborting due to 3 previous errors