Auto merge of #130249 - compiler-errors:sad-new-solver-coherence, r=lcnr

Revert "Stabilize `-Znext-solver=coherence`"

This is a clean revert of #121848, prepared by running:

```
$ git revert 17b322f -m1
```

Which effectively reverts:
* a138a92, 69fdd14, d93e047, 1a893ac

see: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/nalgebra.20hang

Closes #130056

r? lcnr

Author: bors

compiler/rustc_interface/src/tests.rs

@@ -808,7 +808,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(mir_opt_level, Some(4));
     tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, false);
-    tracked!(next_solver, NextSolverConfig { coherence: true, globally: true });
+    tracked!(next_solver, Some(NextSolverConfig { coherence: true, globally: false }));
     tracked!(no_generate_arange_section, true);
     tracked!(no_jump_tables, true);
     tracked!(no_link, true);

compiler/rustc_middle/src/ty/context.rs

@@ -3132,11 +3132,11 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn next_trait_solver_globally(self) -> bool {
-        self.sess.opts.unstable_opts.next_solver.globally
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally)
     }
 
     pub fn next_trait_solver_in_coherence(self) -> bool {
-        self.sess.opts.unstable_opts.next_solver.coherence
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.coherence)
     }
 
     pub fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {

compiler/rustc_session/src/config.rs

@@ -842,11 +842,6 @@ pub struct NextSolverConfig {
     /// This is only `true` if `coherence` is also enabled.
     pub globally: bool,
 }
-impl Default for NextSolverConfig {
-    fn default() -> Self {
-        NextSolverConfig { coherence: true, globally: false }
-    }
-}
 
 #[derive(Clone)]
 pub enum Input {

compiler/rustc_session/src/options.rs

@@ -403,7 +403,7 @@ mod desc {
     pub(crate) const parse_unpretty: &str = "`string` or `string=string`";
     pub(crate) const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
     pub(crate) const parse_next_solver_config: &str =
-        "either `globally` (when used without an argument), `coherence` (default) or `no`";
+        "a comma separated list of solver configurations: `globally` (default), and `coherence`";
     pub(crate) const parse_lto: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted";
     pub(crate) const parse_linker_plugin_lto: &str =
@@ -1105,16 +1105,27 @@ mod parse {
         }
     }
 
-    pub(crate) fn parse_next_solver_config(slot: &mut NextSolverConfig, v: Option<&str>) -> bool {
+    pub(crate) fn parse_next_solver_config(
+        slot: &mut Option<NextSolverConfig>,
+        v: Option<&str>,
+    ) -> bool {
         if let Some(config) = v {
-            *slot = match config {
-                "no" => NextSolverConfig { coherence: false, globally: false },
-                "coherence" => NextSolverConfig { coherence: true, globally: false },
-                "globally" => NextSolverConfig { coherence: true, globally: true },
-                _ => return false,
-            };
+            let mut coherence = false;
+            let mut globally = true;
+            for c in config.split(',') {
+                match c {
+                    "globally" => globally = true,
+                    "coherence" => {
+                        globally = false;
+                        coherence = true;
+                    }
+                    _ => return false,
+                }
+            }
+
+            *slot = Some(NextSolverConfig { coherence: coherence || globally, globally });
         } else {
-            *slot = NextSolverConfig { coherence: true, globally: true };
+            *slot = Some(NextSolverConfig { coherence: true, globally: true });
         }
 
         true
@@ -1867,7 +1878,7 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
-    next_solver: NextSolverConfig = (NextSolverConfig::default(), parse_next_solver_config, [TRACKED],
+    next_solver: Option<NextSolverConfig> = (None, parse_next_solver_config, [TRACKED],
         "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
         "dump facts from NLL analysis into side files (default: no)"),

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -35,8 +35,10 @@ where
         if infcx.next_trait_solver() {
             Box::new(NextFulfillmentCtxt::new(infcx))
         } else {
+            let new_solver_globally =
+                infcx.tcx.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally);
             assert!(
-                !infcx.tcx.next_trait_solver_globally(),
+                !new_solver_globally,
                 "using old solver even though new solver is enabled globally"
             );
             Box::new(FulfillmentContext::new(infcx))

tests/ui/specialization/coherence/default-impl-normalization-ambig-2.rs renamed to tests/crashes/118987-2.rs

@@ -1,4 +1,4 @@
-// regression test for #118987
+//@ known-bug: #118987
 #![feature(specialization)] //~ WARN the feature `specialization` is incomplete
 
 trait Assoc {
@@ -15,5 +15,3 @@ trait Foo {}
 
 impl Foo for <u8 as Assoc>::Output {}
 impl Foo for <u16 as Assoc>::Output {}
-//~^ ERROR the trait bound `u16: Assoc` is not satisfied
-fn main() {}

tests/crashes/118987.rs

@@ -0,0 +1,17 @@
+//@ known-bug: #118987
+#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+
+trait Assoc {
+    type Output;
+}
+
+default impl<T: Clone> Assoc for T {
+    type Output = bool;
+}
+
+impl Assoc for u8 {}
+
+trait Foo {}
+
+impl Foo for <u8 as Assoc>::Output {}
+impl Foo for <u16 as Assoc>::Output {}

tests/ui/transmutability/malformed-program-gracefulness/coherence-bikeshed-intrinsic-from.rs renamed to tests/crashes/124207.rs

@@ -1,11 +1,9 @@
+//@ known-bug: #124207
 #![feature(transmutability)]
 #![feature(type_alias_impl_trait)]
 trait OpaqueTrait {}
 type OpaqueType = impl OpaqueTrait;
-//~^ ERROR unconstrained opaque type
 trait AnotherTrait {}
 impl<T: std::mem::TransmuteFrom<(), ()>> AnotherTrait for T {}
-//~^ ERROR type provided when a constant was expected
 impl AnotherTrait for OpaqueType {}
-//~^ ERROR conflicting implementations of trait `AnotherTrait`
 pub fn main() {}

tests/ui/specialization/coherence/default-item-normalization-ambig-1.rs renamed to tests/crashes/74299.rs

@@ -1,5 +1,5 @@
-// regression test for #73299.
-#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+//@ known-bug: #74299
+#![feature(specialization)]
 
 trait X {
     type U;
@@ -18,7 +18,6 @@ trait Y {
 
 impl Y for <() as X>::U {}
 impl Y for <i32 as X>::U {}
-//~^ ERROR conflicting implementations of trait `Y` for type `<() as X>::U`
 
 fn main() {
     ().f().g();

tests/ui/associated-types/associated-types-coherence-failure.stderr

@@ -1,20 +1,20 @@
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `Cow<'_, _>`
   --> $DIR/associated-types-coherence-failure.rs:21:1
    |
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for <B as ToOwned>::Owned where B: ToOwned {
    | ----------------------------------------------------------------------------- first implementation here
 ...
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for Cow<'a, B> where B: ToOwned {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<_ as ToOwned>::Owned`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Cow<'_, _>`
 
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `&_`
   --> $DIR/associated-types-coherence-failure.rs:28:1
    |
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for <B as ToOwned>::Owned where B: ToOwned {
    | ----------------------------------------------------------------------------- first implementation here
 ...
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for &'a B where B: ToOwned {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<_ as ToOwned>::Owned`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
 
 error: aborting due to 2 previous errors