Rollup merge of rust-lang#117241 - compiler-errors:auto-trait-leak-cy…

…cle, r=oli-obk

Stash and cancel cycle errors for auto trait leakage in opaques

We don't need to emit a traditional cycle error when we have a selection error that explains what's going on but in more detail.

We may want to augment this error to actually point out the cycle, now that the cycle error is not being emitted. We could do that by storing the set of opaques that was in the `CyclePlaceholder` that gets returned from `type_of_opaque`.

r? `@oli-obk` cc `@estebank` rust-lang#117235

compiler/rustc_errors/src/lib.rs

@@ -508,6 +508,8 @@ pub enum StashKey {
     TraitMissingMethod,
     OpaqueHiddenTypeMismatch,
     MaybeForgetReturn,
+    /// Query cycle detected, stashing in favor of a better error.
+    Cycle,
 }
 
 fn default_track_diagnostic(d: &mut Diagnostic, f: &mut dyn FnMut(&mut Diagnostic)) {

compiler/rustc_macros/src/query.rs

@@ -97,6 +97,9 @@ struct QueryModifiers {
     /// A cycle error results in a delay_bug call
     cycle_delay_bug: Option<Ident>,
 
+    /// A cycle error results in a stashed cycle error that can be unstashed and canceled later
+    cycle_stash: Option<Ident>,
+
     /// Don't hash the result, instead just mark a query red if it runs
     no_hash: Option<Ident>,
 
@@ -127,6 +130,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
     let mut desc = None;
     let mut fatal_cycle = None;
     let mut cycle_delay_bug = None;
+    let mut cycle_stash = None;
     let mut no_hash = None;
     let mut anon = None;
     let mut eval_always = None;
@@ -181,6 +185,8 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
             try_insert!(fatal_cycle = modifier);
         } else if modifier == "cycle_delay_bug" {
             try_insert!(cycle_delay_bug = modifier);
+        } else if modifier == "cycle_stash" {
+            try_insert!(cycle_stash = modifier);
         } else if modifier == "no_hash" {
             try_insert!(no_hash = modifier);
         } else if modifier == "anon" {
@@ -208,6 +214,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
         desc,
         fatal_cycle,
         cycle_delay_bug,
+        cycle_stash,
         no_hash,
         anon,
         eval_always,
@@ -329,6 +336,7 @@ pub fn rustc_queries(input: TokenStream) -> TokenStream {
             fatal_cycle,
             arena_cache,
             cycle_delay_bug,
+            cycle_stash,
             no_hash,
             anon,
             eval_always,

compiler/rustc_middle/src/query/mod.rs

@@ -251,6 +251,7 @@ rustc_queries! {
             "computing type of opaque `{path}`",
             path = tcx.def_path_str(key),
         }
+        cycle_stash
     }
 
     query type_alias_is_lazy(key: DefId) -> bool {

compiler/rustc_query_impl/src/plumbing.rs

@@ -197,6 +197,9 @@ macro_rules! handle_cycle_error {
     ([(fatal_cycle) $($rest:tt)*]) => {{
         rustc_query_system::HandleCycleError::Fatal
     }};
+    ([(cycle_stash) $($rest:tt)*]) => {{
+        rustc_query_system::HandleCycleError::Stash
+    }};
     ([(cycle_delay_bug) $($rest:tt)*]) => {{
         rustc_query_system::HandleCycleError::DelayBug
     }};

compiler/rustc_query_system/src/error.rs

@@ -15,6 +15,7 @@ pub enum HandleCycleError {
     Error,
     Fatal,
     DelayBug,
+    Stash,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_query_system/src/query/plumbing.rs

@@ -19,7 +19,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lock;
 #[cfg(parallel_compiler)]
 use rustc_data_structures::{outline, sync};
-use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, FatalError};
+use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, FatalError, StashKey};
 use rustc_span::{Span, DUMMY_SP};
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
@@ -133,6 +133,17 @@ where
             let guar = error.delay_as_bug();
             query.value_from_cycle_error(*qcx.dep_context(), &cycle_error.cycle, guar)
         }
+        Stash => {
+            let guar = if let Some(root) = cycle_error.cycle.first()
+                && let Some(span) = root.query.span
+            {
+                error.stash(span, StashKey::Cycle);
+                qcx.dep_context().sess().delay_span_bug(span, "delayed cycle error")
+            } else {
+                error.emit()
+            };
+            query.value_from_cycle_error(*qcx.dep_context(), &cycle_error.cycle, guar)
+        }
     }
 }
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -3104,6 +3104,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 );
             }
         };
+
+        if let Some(diag) =
+            self.tcx.sess.diagnostic().steal_diagnostic(self.tcx.def_span(def_id), StashKey::Cycle)
+        {
+            diag.cancel();
+        }
+
         err
     }
 

tests/ui/impl-trait/auto-trait-leak.rs

@@ -9,8 +9,6 @@ fn main() {}
 // independently resolved and only require the concrete
 // return type, which can't depend on the obligation.
 fn cycle1() -> impl Clone {
-    //~^ ERROR cycle detected
-    //~| ERROR cycle detected
     send(cycle2().clone());
 
     Rc::new(Cell::new(5))

tests/ui/impl-trait/auto-trait-leak.stderr

@@ -1,66 +1,5 @@
-error[E0391]: cycle detected when computing type of opaque `cycle1::{opaque#0}`
-  --> $DIR/auto-trait-leak.rs:11:16
-   |
-LL | fn cycle1() -> impl Clone {
-   |                ^^^^^^^^^^
-   |
-note: ...which requires type-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:14:5
-   |
-LL |     send(cycle2().clone());
-   |     ^^^^
-   = note: ...which requires evaluating trait selection obligation `cycle2::{opaque#0}: core::marker::Send`...
-note: ...which requires computing type of opaque `cycle2::{opaque#0}`...
-  --> $DIR/auto-trait-leak.rs:19:16
-   |
-LL | fn cycle2() -> impl Clone {
-   |                ^^^^^^^^^^
-note: ...which requires type-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:5
-   |
-LL |     send(cycle1().clone());
-   |     ^^^^
-   = note: ...which requires evaluating trait selection obligation `cycle1::{opaque#0}: core::marker::Send`...
-   = note: ...which again requires computing type of opaque `cycle1::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `cycle1::{opaque#0}`
-  --> $DIR/auto-trait-leak.rs:11:16
-   |
-LL | fn cycle1() -> impl Clone {
-   |                ^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
-error[E0391]: cycle detected when computing type of opaque `cycle1::{opaque#0}`
-  --> $DIR/auto-trait-leak.rs:11:16
-   |
-LL | fn cycle1() -> impl Clone {
-   |                ^^^^^^^^^^
-   |
-note: ...which requires type-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:14:5
-   |
-LL |     send(cycle2().clone());
-   |     ^^^^
-   = note: ...which requires evaluating trait selection obligation `cycle2::{opaque#0}: core::marker::Send`...
-note: ...which requires computing type of opaque `cycle2::{opaque#0}`...
-  --> $DIR/auto-trait-leak.rs:19:16
-   |
-LL | fn cycle2() -> impl Clone {
-   |                ^^^^^^^^^^
-note: ...which requires type-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:19:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: ...which again requires computing type of opaque `cycle1::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `cycle1::{opaque#0}`
-  --> $DIR/auto-trait-leak.rs:11:16
-   |
-LL | fn cycle1() -> impl Clone {
-   |                ^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
 error: cannot check whether the hidden type of opaque type satisfies auto traits
-  --> $DIR/auto-trait-leak.rs:20:10
+  --> $DIR/auto-trait-leak.rs:18:10
    |
 LL |     send(cycle1().clone());
    |     ---- ^^^^^^^^^^^^^^^^
@@ -73,7 +12,7 @@ note: opaque type is declared here
 LL | fn cycle1() -> impl Clone {
    |                ^^^^^^^^^^
 note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
-  --> $DIR/auto-trait-leak.rs:19:4
+  --> $DIR/auto-trait-leak.rs:17:4
    |
 LL | fn cycle2() -> impl Clone {
    |    ^^^^^^
@@ -83,6 +22,5 @@ note: required by a bound in `send`
 LL | fn send<T: Send>(_: T) {}
    |            ^^^^ required by this bound in `send`
 
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0391`.

tests/ui/type-alias-impl-trait/auto-trait-leakage3.rs

@@ -5,9 +5,6 @@
 
 mod m {
     pub type Foo = impl std::fmt::Debug;
-    //~^ ERROR: cycle detected when computing type of opaque `m::Foo::{opaque#0}` [E0391]
-    //~| ERROR: cycle detected when computing type of opaque `m::Foo::{opaque#0}` [E0391]
-
     pub fn foo() -> Foo {
         22_u32
     }

tests/ui/type-alias-impl-trait/auto-trait-leakage3.stderr

@@ -1,44 +1,5 @@
-error[E0391]: cycle detected when computing type of opaque `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/auto-trait-leakage3.rs:16:9
-   |
-LL |         is_send(foo());
-   |         ^^^^^^^
-   = note: ...which requires evaluating trait selection obligation `m::Foo: core::marker::Send`...
-   = note: ...which again requires computing type of opaque `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
-error[E0391]: cycle detected when computing type of opaque `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/auto-trait-leakage3.rs:15:5
-   |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
-   = note: ...which again requires computing type of opaque `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
 error: cannot check whether the hidden type of `auto_trait_leakage3[211d]::m::Foo::{opaque#0}` satisfies auto traits
-  --> $DIR/auto-trait-leakage3.rs:16:17
+  --> $DIR/auto-trait-leakage3.rs:13:17
    |
 LL |         is_send(foo());
    |         ------- ^^^^^
@@ -51,16 +12,15 @@ note: opaque type is declared here
 LL |     pub type Foo = impl std::fmt::Debug;
    |                    ^^^^^^^^^^^^^^^^^^^^
 note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
-  --> $DIR/auto-trait-leakage3.rs:15:12
+  --> $DIR/auto-trait-leakage3.rs:12:12
    |
 LL |     pub fn bar() {
    |            ^^^
 note: required by a bound in `is_send`
-  --> $DIR/auto-trait-leakage3.rs:20:19
+  --> $DIR/auto-trait-leakage3.rs:17:19
    |
 LL |     fn is_send<T: Send>(_: T) {}
    |                   ^^^^ required by this bound in `is_send`
 
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0391`.

tests/ui/type-alias-impl-trait/inference-cycle.rs

@@ -3,17 +3,14 @@
 
 mod m {
     pub type Foo = impl std::fmt::Debug;
-    //~^ ERROR cycle detected
-    //~| ERROR cycle detected
-
-    // Cycle: error today, but it'd be nice if it eventually worked
 
     pub fn foo() -> Foo {
         is_send(bar())
     }
 
     pub fn bar() {
-        is_send(foo()); // Today: error
+        // Cycle: error today, but it'd be nice if it eventually worked
+        is_send(foo());
         //~^ ERROR: cannot check whether the hidden type of `inference_cycle[4ecc]::m::Foo::{opaque#0}` satisfies auto traits
     }
 

tests/ui/type-alias-impl-trait/inference-cycle.stderr

@@ -1,46 +1,7 @@
-error[E0391]: cycle detected when computing type of opaque `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/inference-cycle.rs:16:9
-   |
-LL |         is_send(foo()); // Today: error
-   |         ^^^^^^^
-   = note: ...which requires evaluating trait selection obligation `m::Foo: core::marker::Send`...
-   = note: ...which again requires computing type of opaque `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
-error[E0391]: cycle detected when computing type of opaque `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/inference-cycle.rs:15:5
-   |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
-   = note: ...which again requires computing type of opaque `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:20
-   |
-LL |     pub type Foo = impl std::fmt::Debug;
-   |                    ^^^^^^^^^^^^^^^^^^^^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
 error: cannot check whether the hidden type of `inference_cycle[4ecc]::m::Foo::{opaque#0}` satisfies auto traits
-  --> $DIR/inference-cycle.rs:16:17
+  --> $DIR/inference-cycle.rs:13:17
    |
-LL |         is_send(foo()); // Today: error
+LL |         is_send(foo());
    |         ------- ^^^^^
    |         |
    |         required by a bound introduced by this call
@@ -51,16 +12,15 @@ note: opaque type is declared here
 LL |     pub type Foo = impl std::fmt::Debug;
    |                    ^^^^^^^^^^^^^^^^^^^^
 note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
-  --> $DIR/inference-cycle.rs:15:12
+  --> $DIR/inference-cycle.rs:11:12
    |
 LL |     pub fn bar() {
    |            ^^^
 note: required by a bound in `is_send`
-  --> $DIR/inference-cycle.rs:24:19
+  --> $DIR/inference-cycle.rs:21:19
    |
 LL |     fn is_send<T: Send>(_: T) {}
    |                   ^^^^ required by this bound in `is_send`
 
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0391`.

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

@@ -3,9 +3,6 @@
 use std::fmt::Debug;
 
 type Foo = impl Debug;
-//~^ ERROR cycle detected
-//~| ERROR cycle detected
-//~| ERROR cycle detected
 
 fn is_send<T: Send>() {}