Give me a way to emit all the delayed bugs

compiler/rustc_errors/src/lib.rs

@@ -527,6 +527,9 @@ pub struct DiagCtxtFlags {
     /// If Some, the Nth error-level diagnostic is upgraded to bug-level.
     /// (rustc: see `-Z treat-err-as-bug`)
     pub treat_err_as_bug: Option<NonZeroUsize>,
+    /// Eagerly emit delayed bugs as errors, so that the compiler debugger may
+    /// see all of the errors being emitted at once.
+    pub eagerly_emit_delayed_bugs: bool,
     /// Show macro backtraces.
     /// (rustc: see `-Z macro-backtrace`)
     pub macro_backtrace: bool,
@@ -1269,16 +1272,21 @@ impl DiagCtxtInner {
         }
 
         if diagnostic.level == DelayedBug {
-            // FIXME(eddyb) this should check for `has_errors` and stop pushing
-            // once *any* errors were emitted (and truncate `span_delayed_bugs`
-            // when an error is first emitted, also), but maybe there's a case
-            // in which that's not sound? otherwise this is really inefficient.
-            let backtrace = std::backtrace::Backtrace::capture();
-            self.span_delayed_bugs
-                .push(DelayedDiagnostic::with_backtrace(diagnostic.clone(), backtrace));
+            if self.flags.eagerly_emit_delayed_bugs {
+                // Emit error as bug, rather than stashing it.
+                diagnostic.level = Error;
+            } else {
+                // FIXME(eddyb) this should check for `has_errors` and stop pushing
+                // once *any* errors were emitted (and truncate `span_delayed_bugs`
+                // when an error is first emitted, also), but maybe there's a case
+                // in which that's not sound? otherwise this is really inefficient.
+                let backtrace = std::backtrace::Backtrace::capture();
+                self.span_delayed_bugs
+                    .push(DelayedDiagnostic::with_backtrace(diagnostic.clone(), backtrace));
 
-            #[allow(deprecated)]
-            return Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
+                #[allow(deprecated)]
+                return Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
+            }
         }
 
         if diagnostic.has_future_breakage() {

compiler/rustc_session/src/config.rs

@@ -1146,6 +1146,7 @@ impl UnstableOptions {
         DiagCtxtFlags {
             can_emit_warnings,
             treat_err_as_bug: self.treat_err_as_bug,
+            eagerly_emit_delayed_bugs: self.eagerly_emit_delayed_bugs,
             macro_backtrace: self.macro_backtrace,
             deduplicate_diagnostics: self.deduplicate_diagnostics,
             track_diagnostics: self.track_diagnostics,

compiler/rustc_session/src/options.rs

@@ -1583,6 +1583,9 @@ options! {
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     dylib_lto: bool = (false, parse_bool, [UNTRACKED],
         "enables LTO for dylib crate type"),
+    eagerly_emit_delayed_bugs: bool = (false, parse_bool, [UNTRACKED],
+        "emit delayed bugs eagerly as errors instead of stashing them and emitting \
+        them only if an error has not been emitted"),
     ehcont_guard: bool = (false, parse_bool, [TRACKED],
         "generate Windows EHCont Guard tables"),
     emit_stack_sizes: bool = (false, parse_bool, [UNTRACKED],

tests/ui/treat-err-as-bug/eagerly-emit.rs

@@ -0,0 +1,11 @@
+// compile-flags: -Zeagerly-emit-delayed-bugs
+
+trait Foo {}
+
+fn main() {}
+
+fn f() -> impl Foo {
+    //~^ ERROR the trait bound `i32: Foo` is not satisfied
+    //~| ERROR `report_selection_error` did not emit an error
+    1i32
+}

tests/ui/treat-err-as-bug/eagerly-emit.stderr

@@ -0,0 +1,26 @@
+error: `report_selection_error` did not emit an error
+  --> $DIR/eagerly-emit.rs:7:11
+   |
+LL | fn f() -> impl Foo {
+   |           ^^^^^^^^
+
+error[E0277]: the trait bound `i32: Foo` is not satisfied
+  --> $DIR/eagerly-emit.rs:7:11
+   |
+LL | fn f() -> impl Foo {
+   |           ^^^^^^^^ the trait `Foo` is not implemented for `i32`
+...
+LL |     1i32
+   |     ---- return type was inferred to be `i32` here
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/eagerly-emit.rs:3:1
+   |
+LL | trait Foo {}
+   | ^^^^^^^^^
+
+error: expected fulfillment errors
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.