Don't consider delayed bugs for -Ztreat-err-as-bug.

`-Ztreat-err-as-bug` treats normal errors and delayed bugs equally,
which can lead to some really surprising results.

This commit changes `-Ztreat-err-as-bug` so it ignores delayed bugs,
unless they get promoted to proper bugs and are printed.

This feels to me much simpler and more logical. And it simplifies the
implementation:
- The `-Ztreat-err-as-bug` check is removed from in
  `DiagCtxt::{delayed_bug,span_delayed_bug}`.
- `treat_err_as_bug` doesn't need to count delayed bugs.
- The `-Ztreat-err-as-bug` panic message is simpler, because it doesn't
  have to mention delayed bugs.

Output of delayed bugs is now more consistent. They're always printed
the same way. Previously when they triggered `-Ztreat-err-as-bug` they
would be printed slightly differently, via `span_bug` in
`span_delayed_bug` or `delayed_bug`.

A minor behaviour change: the "no errors encountered even though
`span_delayed_bug` issued" printed before delayed bugs is now a note
rather than a bug. This is done so it doesn't get counted as an error
that might trigger `-Ztreat-err-as-bug`, which would be silly.
This means that if you use `-Ztreat-err-as-bug=1` and there are no
normal errors but there are delayed bugs, the first delayed bug will be
shown (and the panic will happen after it's printed).

Also, I have added a second note saying "those delayed bugs will now be
shown as internal compiler errors". I think this makes it clearer what
is happening, because the whole concept of delayed bugs is non-obvious.

There are some test changes.
- equality-in-canonical-query.rs: Minor output changes, and the error
  count reduces by one because the "no errors encountered even though
  `span_delayed_bug` issued" message is no longer counted as an error.
- rpit_tait_equality_in_canonical_query.rs: Ditto.
- storage-live.rs: The query stack disappears because these delayed bugs
  are now printed at the end, rather than when they are created.
- storage-return.rs, span_delayed_bug.rs: now need
  `-Zeagerly-emit-delayed-bugs` because they need the delayed bugs
  emitted immediately to preserve behaviour.

compiler/rustc_errors/src/lib.rs

@@ -865,10 +865,6 @@ impl DiagCtxt {
     /// directly).
     #[track_caller]
     pub fn delayed_bug(&self, msg: impl Into<DiagnosticMessage>) -> ErrorGuaranteed {
-        let treat_next_err_as_bug = self.inner.borrow().treat_next_err_as_bug();
-        if treat_next_err_as_bug {
-            self.bug(msg);
-        }
         DiagnosticBuilder::<ErrorGuaranteed>::new(self, DelayedBug(DelayedBugKind::Normal), msg)
             .emit()
     }
@@ -883,10 +879,6 @@ impl DiagCtxt {
         sp: impl Into<MultiSpan>,
         msg: impl Into<DiagnosticMessage>,
     ) -> ErrorGuaranteed {
-        let treat_next_err_as_bug = self.inner.borrow().treat_next_err_as_bug();
-        if treat_next_err_as_bug {
-            self.span_bug(sp, msg);
-        }
         DiagnosticBuilder::<ErrorGuaranteed>::new(self, DelayedBug(DelayedBugKind::Normal), msg)
             .with_span(sp)
             .emit()
@@ -1259,10 +1251,6 @@ impl DiagCtxtInner {
     }
 
     fn emit_diagnostic(&mut self, mut diagnostic: Diagnostic) -> Option<ErrorGuaranteed> {
-        if matches!(diagnostic.level, Error | Fatal) && self.treat_next_err_as_bug() {
-            diagnostic.level = Bug;
-        }
-
         // The `LintExpectationId` can be stable or unstable depending on when it was created.
         // Diagnostics created before the definition of `HirId`s are unstable and can not yet
         // be stored. Instead, they are buffered until the `LintExpectationId` is replaced by
@@ -1298,6 +1286,12 @@ impl DiagCtxtInner {
             _ => {}
         }
 
+        // This must come after the possible promotion of `DelayedBug` to
+        // `Error` above.
+        if matches!(diagnostic.level, Error | Fatal) && self.treat_next_err_as_bug() {
+            diagnostic.level = Bug;
+        }
+
         if diagnostic.has_future_breakage() {
             // Future breakages aren't emitted if they're Level::Allow,
             // but they still need to be constructed and stashed below,
@@ -1387,20 +1381,14 @@ impl DiagCtxtInner {
     }
 
     fn treat_err_as_bug(&self) -> bool {
-        self.flags.treat_err_as_bug.is_some_and(|c| {
-            self.err_count + self.lint_err_count + self.delayed_bug_count() >= c.get()
-        })
+        self.flags.treat_err_as_bug.is_some_and(|c| self.err_count + self.lint_err_count >= c.get())
     }
 
     // Use this one before incrementing `err_count`.
     fn treat_next_err_as_bug(&self) -> bool {
-        self.flags.treat_err_as_bug.is_some_and(|c| {
-            self.err_count + self.lint_err_count + self.delayed_bug_count() + 1 >= c.get()
-        })
-    }
-
-    fn delayed_bug_count(&self) -> usize {
-        self.span_delayed_bugs.len() + self.good_path_delayed_bugs.len()
+        self.flags
+            .treat_err_as_bug
+            .is_some_and(|c| self.err_count + self.lint_err_count + 1 >= c.get())
     }
 
     fn has_errors(&self) -> bool {
@@ -1412,7 +1400,7 @@ impl DiagCtxtInner {
     }
 
     fn flush_delayed(&mut self, kind: DelayedBugKind) {
-        let (bugs, explanation) = match kind {
+        let (bugs, note1) = match kind {
             DelayedBugKind::Normal => (
                 std::mem::take(&mut self.span_delayed_bugs),
                 "no errors encountered even though `span_delayed_bug` issued",
@@ -1422,6 +1410,7 @@ impl DiagCtxtInner {
                 "no warnings or errors encountered even though `good_path_delayed_bugs` issued",
             ),
         };
+        let note2 = "those delayed bugs will now be shown as internal compiler errors";
 
         if bugs.is_empty() {
             return;
@@ -1447,8 +1436,11 @@ impl DiagCtxtInner {
 
             if i == 0 {
                 // Put the overall explanation before the `DelayedBug`s, to
-                // frame them better (e.g. separate warnings from them).
-                self.emit_diagnostic(Diagnostic::new(Bug, explanation));
+                // frame them better (e.g. separate warnings from them). Also,
+                // make it a note so it doesn't count as an error, because that
+                // could trigger `-Ztreat-err-as-bug`, which we don't want.
+                self.emit_diagnostic(Diagnostic::new(Note, note1));
+                self.emit_diagnostic(Diagnostic::new(Note, note2));
             }
 
             let mut bug =
@@ -1474,22 +1466,12 @@ impl DiagCtxtInner {
 
     fn panic_if_treat_err_as_bug(&self) {
         if self.treat_err_as_bug() {
-            match (
-                self.err_count + self.lint_err_count,
-                self.delayed_bug_count(),
-                self.flags.treat_err_as_bug.map(|c| c.get()).unwrap(),
-            ) {
-                (1, 0, 1) => panic!("aborting due to `-Z treat-err-as-bug=1`"),
-                (0, 1, 1) => panic!("aborting due delayed bug with `-Z treat-err-as-bug=1`"),
-                (count, delayed_count, val) => {
-                    if delayed_count > 0 {
-                        panic!(
-                            "aborting after {count} errors and {delayed_count} delayed bugs due to `-Z treat-err-as-bug={val}`",
-                        )
-                    } else {
-                        panic!("aborting after {count} errors due to `-Z treat-err-as-bug={val}`")
-                    }
-                }
+            let n = self.flags.treat_err_as_bug.map(|c| c.get()).unwrap();
+            assert_eq!(n, self.err_count + self.lint_err_count);
+            if n == 1 {
+                panic!("aborting due to `-Z treat-err-as-bug=1`");
+            } else {
+                panic!("aborting after {n} errors due to `-Z treat-err-as-bug={n}`");
             }
         }
     }

tests/ui/impl-trait/equality-in-canonical-query.clone.stderr

@@ -1,29 +1,25 @@
-error: internal compiler error: no errors encountered even though `span_delayed_bug` issued
+note: no errors encountered even though `span_delayed_bug` issued
+
+note: those delayed bugs will now be shown as internal compiler errors
 
 error: internal compiler error: {OpaqueTypeKey { def_id: DefId(rpit::{opaque#0}), args: [] }: OpaqueTypeDecl { hidden_type: OpaqueHiddenType { span: no-location (#0), ty: Alias(Opaque, AliasTy { args: [], def_id: DefId(foo::{opaque#0}) }) } }}
    |
    = 
 
 
 error: internal compiler error: error performing ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: ProvePredicate { predicate: Binder { value: ProjectionPredicate(AliasTy { args: [FnDef(DefId(rpit), []), ()], def_id: DefId(ops::function::FnOnce::Output) }, Term::Ty(Alias(Opaque, AliasTy { args: [], def_id: DefId(foo::{opaque#0}) }))), bound_vars: [] } } }
-  --> $DIR/equality-in-canonical-query.rs:19:5
+  --> $DIR/equality-in-canonical-query.rs:21:5
    |
 LL |     same_output(foo, rpit);
    |     ^^^^^^^^^^^^^^^^^^^^^^
    |
 
-  --> $DIR/equality-in-canonical-query.rs:19:5
+  --> $DIR/equality-in-canonical-query.rs:21:5
    |
 LL |     same_output(foo, rpit);
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
-
-
-
-
-
-
 query stack during panic:
 end of query stack
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/ui/impl-trait/equality-in-canonical-query.rs

@@ -1,11 +1,13 @@
 // issue: #116877
 // revisions: sized clone
 //[sized] check-pass
-
 //[clone] known-bug: #108498
 //[clone] failure-status: 101
 //[clone] normalize-stderr-test: "DefId\(.*?\]::" -> "DefId("
-//[clone] normalize-stderr-test: "(?m)note: .*$" -> ""
+//[clone] normalize-stderr-test: "(?m)note: we would appreciate a bug report.*\n\n" -> ""
+//[clone] normalize-stderr-test: "(?m)note: rustc.*running on.*\n\n" -> ""
+//[clone] normalize-stderr-test: "(?m)note: compiler flags.*\n\n" -> ""
+//[clone] normalize-stderr-test: "(?m)note: delayed at.*$" -> ""
 //[clone] normalize-stderr-test: "(?m)^ *\d+: .*\n" -> ""
 //[clone] normalize-stderr-test: "(?m)^ *at .*\n" -> ""
 

tests/ui/mir/lint/storage-live.stderr

@@ -2,13 +2,17 @@ error: internal compiler error: broken MIR in Item(DefId(0:8 ~ storage_live[HASH
                                 StorageLive(_1) which already has storage here
   --> $DIR/storage-live.rs:22:13
    |
+LL |             StorageLive(a);
+   |             ^^^^^^^^^^^^^^
+   |
+note: delayed at compiler/rustc_mir_transform/src/lint.rs:97:26 - disabled backtrace
+  --> $DIR/storage-live.rs:22:13
+   |
 LL |             StorageLive(a);
    |             ^^^^^^^^^^^^^^
 
 aborting due to `-Z treat-err-as-bug=1`
 error: the compiler unexpectedly panicked. this is a bug.
 
 query stack during panic:
-#0 [mir_const] preparing `multiple_storage` for borrow checking
-#1 [mir_promoted] promoting constants in MIR for `multiple_storage`
 end of query stack

tests/ui/mir/lint/storage-return.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zlint-mir -Ztreat-err-as-bug
+// compile-flags: -Zlint-mir -Ztreat-err-as-bug -Zeagerly-emit-delayed-bugs
 // failure-status: 101
 // dont-check-compiler-stderr
 // error-pattern: has storage when returning

tests/ui/treat-err-as-bug/span_delayed_bug.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Ztreat-err-as-bug
+// compile-flags: -Ztreat-err-as-bug -Zeagerly-emit-delayed-bugs
 // failure-status: 101
 // error-pattern: aborting due to `-Z treat-err-as-bug=1`
 // error-pattern: [trigger_span_delayed_bug] triggering a span delayed bug for testing incremental

tests/ui/type-alias-impl-trait/rpit_tait_equality_in_canonical_query.current.stderr

@@ -1,29 +1,25 @@
-error: internal compiler error: no errors encountered even though `span_delayed_bug` issued
+note: no errors encountered even though `span_delayed_bug` issued
+
+note: those delayed bugs will now be shown as internal compiler errors
 
 error: internal compiler error: {OpaqueTypeKey { def_id: DefId(get_rpit::{opaque#0}), args: [] }: OpaqueTypeDecl { hidden_type: OpaqueHiddenType { span: no-location (#0), ty: Alias(Opaque, AliasTy { args: [], def_id: DefId(Opaque::{opaque#0}) }) } }}
    |
    = 
 
 
 error: internal compiler error: error performing ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: ProvePredicate { predicate: Binder { value: ProjectionPredicate(AliasTy { args: [FnDef(DefId(get_rpit), []), ()], def_id: DefId(ops::function::FnOnce::Output) }, Term::Ty(Alias(Opaque, AliasTy { args: [], def_id: DefId(Opaque::{opaque#0}) }))), bound_vars: [] } } }
-  --> $DIR/rpit_tait_equality_in_canonical_query.rs:28:5
+  --> $DIR/rpit_tait_equality_in_canonical_query.rs:31:5
    |
 LL |     query(get_rpit);
    |     ^^^^^^^^^^^^^^^
    |
 
-  --> $DIR/rpit_tait_equality_in_canonical_query.rs:28:5
+  --> $DIR/rpit_tait_equality_in_canonical_query.rs:31:5
    |
 LL |     query(get_rpit);
    |     ^^^^^^^^^^^^^^^
 
-
-
-
-
-
-
 query stack during panic:
 end of query stack
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/ui/type-alias-impl-trait/rpit_tait_equality_in_canonical_query.rs

@@ -12,7 +12,10 @@
 //[current] known-bug: #108498
 //[current] failure-status: 101
 //[current] normalize-stderr-test: "DefId\(.*?\]::" -> "DefId("
-//[current] normalize-stderr-test: "(?m)note: .*$" -> ""
+//[current] normalize-stderr-test: "(?m)note: we would appreciate a bug report.*\n\n" -> ""
+//[current] normalize-stderr-test: "(?m)note: rustc.*running on.*\n\n" -> ""
+//[current] normalize-stderr-test: "(?m)note: compiler flags.*\n\n" -> ""
+//[current] normalize-stderr-test: "(?m)note: delayed at.*$" -> ""
 //[current] normalize-stderr-test: "(?m)^ *\d+: .*\n" -> ""
 //[current] normalize-stderr-test: "(?m)^ *at .*\n" -> ""