Include compiler flags when you break rust;

compiler/rustc_hir_typeck/src/lib.rs

@@ -436,6 +436,12 @@ fn fatally_break_rust(tcx: TyCtxt<'_>) {
         tcx.sess.cfg_version,
         config::host_triple(),
     ));
+    if let Some((flags, excluded_cargo_defaults)) = rustc_session::utils::extra_compiler_flags() {
+        handler.note_without_error(format!("compiler flags: {}", flags.join(" ")));
+        if excluded_cargo_defaults {
+            handler.note_without_error("some of the compiler flags provided by cargo are hidden");
+        }
+    }
 }
 
 fn has_expected_num_generic_args(tcx: TyCtxt<'_>, trait_did: DefId, expected: usize) -> bool {

tests/ui/track-diagnostics/track.rs

@@ -6,6 +6,11 @@
 // normalize-stderr-test ".rs:\d+:\d+" -> ".rs:LL:CC"
 // normalize-stderr-test "note: rustc .+ running on .+" -> "note: rustc $$VERSION running on $$TARGET"
 
+// The test becomes too flaky if we care about exact args. If `-Z ui-testing`
+// from compiletest and `-Z track-diagnostics` from `// compile-flags` at the
+// top of this file are present, then assume all args are present.
+// normalize-stderr-test "note: compiler flags: .*-Z ui-testing.*-Z track-diagnostics" -> "note: compiler flags: ... -Z ui-testing ... -Z track-diagnostics"
+
 fn main() {
     break rust
 }

tests/ui/track-diagnostics/track.stderr

@@ -20,6 +20,8 @@ note: we would appreciate a joke overview: https://github.com/rust-lang/rust/iss
 
 note: rustc $VERSION running on $TARGET
 
+note: compiler flags: ... -Z ui-testing ... -Z track-diagnostics
+
 error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0268, E0425.