Rollup merge of #127687 - RalfJung:pattern-cleanup, r=oli-obk,lcnr

Const-to-pattern-to-MIR cleanup

Now that all uses of constants without structural equality are hard errors, there's a bunch of cleanup we can do in the code that handles patterns: we can always funnel patterns through valtrees first (rather than having a fallback path for when valtree construction fails), and we can make sure that if we emit a `PartialEq` call it is not calling anything user-defined.

To keep the error messages the same, I made valtree construction failures return the information of *which* type it is that cannot be valtree'd. `search_for_structural_match_violation` is now not needed any more at all, so I removed it.

r? `@oli-obk`

17 files changed, 70 insertions, 108 deletions

diff --git a/tests/ui/associated-consts/associated-const-type-parameter-arms.stderr b/tests/ui/associated-consts/associated-const-type-parameter-arms.stderr
deleted file mode 100644
index 1ccf9febd4b..00000000000
--- a/tests/ui/associated-consts/associated-const-type-parameter-arms.stderr
+++ /dev/null
@@ -1,15 +0,0 @@
-error[E0158]: associated consts cannot be referenced in patterns
-  --> $DIR/associated-const-type-parameter-arms.rs:20:9
-   |
-LL |         A::X => println!("A::X"),
-   |         ^^^^
-
-error[E0158]: associated consts cannot be referenced in patterns
-  --> $DIR/associated-const-type-parameter-arms.rs:22:9
-   |
-LL |         B::X => println!("B::X"),
-   |         ^^^^
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/associated-consts/associated-const-type-parameter-arms.rs b/tests/ui/associated-consts/associated-const-type-parameter-pattern.rs
index 3f260d84e4c..b5798adc71c 100644
--- a/tests/ui/associated-consts/associated-const-type-parameter-arms.rs
+++ b/tests/ui/associated-consts/associated-const-type-parameter-pattern.rs
@@ -18,12 +18,18 @@ impl Foo for Def {
 pub fn test<A: Foo, B: Foo>(arg: EFoo) {
     match arg {
         A::X => println!("A::X"),
-        //~^ error: associated consts cannot be referenced in patterns [E0158]
+        //~^ error: constant pattern depends on a generic parameter
         B::X => println!("B::X"),
-        //~^ error: associated consts cannot be referenced in patterns [E0158]
+        //~^ error: constant pattern depends on a generic parameter
         _ => (),
     }
 }
 
+pub fn test_let_pat<A: Foo, B: Foo>(arg: EFoo, A::X: EFoo) {
+    //~^ ERROR constant pattern depends on a generic parameter
+    let A::X = arg;
+    //~^ ERROR constant pattern depends on a generic parameter
+}
+
 fn main() {
 }
diff --git a/tests/ui/associated-consts/associated-const-type-parameter-pattern.stderr b/tests/ui/associated-consts/associated-const-type-parameter-pattern.stderr
new file mode 100644
index 00000000000..adc8f399207
--- /dev/null
+++ b/tests/ui/associated-consts/associated-const-type-parameter-pattern.stderr
@@ -0,0 +1,27 @@
+error[E0158]: constant pattern depends on a generic parameter
+  --> $DIR/associated-const-type-parameter-pattern.rs:20:9
+   |
+LL |         A::X => println!("A::X"),
+   |         ^^^^
+
+error[E0158]: constant pattern depends on a generic parameter
+  --> $DIR/associated-const-type-parameter-pattern.rs:22:9
+   |
+LL |         B::X => println!("B::X"),
+   |         ^^^^
+
+error[E0158]: constant pattern depends on a generic parameter
+  --> $DIR/associated-const-type-parameter-pattern.rs:30:9
+   |
+LL |     let A::X = arg;
+   |         ^^^^
+
+error[E0158]: constant pattern depends on a generic parameter
+  --> $DIR/associated-const-type-parameter-pattern.rs:28:48
+   |
+LL | pub fn test_let_pat<A: Foo, B: Foo>(arg: EFoo, A::X: EFoo) {
+   |                                                ^^^^
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/consts/const_in_pattern/custom-eq-branch-pass.rs b/tests/ui/consts/const_in_pattern/custom-eq-branch-pass.rs
index 2e7061e7c4b..ab8eec876bc 100644
--- a/tests/ui/consts/const_in_pattern/custom-eq-branch-pass.rs
+++ b/tests/ui/consts/const_in_pattern/custom-eq-branch-pass.rs
@@ -23,9 +23,20 @@ const BAR_BAZ: Foo = if 42 == 42 {
     Foo::Qux(CustomEq) // dead arm
 };
 
+const EMPTY: &[CustomEq] = &[];
+
 fn main() {
+    // BAR_BAZ itself is fine but the enum has other variants
+    // that are non-structural. Still, this should be accepted.
     match Foo::Qux(CustomEq) {
         BAR_BAZ => panic!(),
         _ => {}
     }
+
+    // Similarly, an empty slice of a type that is non-structural
+    // is accepted.
+    match &[CustomEq] as &[CustomEq] {
+        EMPTY => panic!(),
+        _ => {},
+    }
 }
diff --git a/tests/ui/consts/const_in_pattern/reject_non_partial_eq.rs b/tests/ui/consts/const_in_pattern/reject_non_partial_eq.rs
index 86d971044fe..645e1418912 100644
--- a/tests/ui/consts/const_in_pattern/reject_non_partial_eq.rs
+++ b/tests/ui/consts/const_in_pattern/reject_non_partial_eq.rs
@@ -26,7 +26,7 @@ fn main() {
 
     match None {
         NO_PARTIAL_EQ_NONE => println!("NO_PARTIAL_EQ_NONE"),
-        //~^ ERROR must be annotated with `#[derive(PartialEq)]`
+        //~^ ERROR must implement `PartialEq`
         _ => panic!("whoops"),
     }
 }
diff --git a/tests/ui/consts/const_in_pattern/reject_non_partial_eq.stderr b/tests/ui/consts/const_in_pattern/reject_non_partial_eq.stderr
index 88b82d5004b..ed531a1fead 100644
--- a/tests/ui/consts/const_in_pattern/reject_non_partial_eq.stderr
+++ b/tests/ui/consts/const_in_pattern/reject_non_partial_eq.stderr
@@ -1,11 +1,8 @@
-error: to use a constant of type `NoPartialEq` in a pattern, `NoPartialEq` must be annotated with `#[derive(PartialEq)]`
+error: to use a constant of type `Option<NoPartialEq>` in a pattern, the type must implement `PartialEq`
   --> $DIR/reject_non_partial_eq.rs:28:9
    |
 LL |         NO_PARTIAL_EQ_NONE => println!("NO_PARTIAL_EQ_NONE"),
    |         ^^^^^^^^^^^^^^^^^^
-   |
-   = note: the traits must be derived, manual `impl`s are not sufficient
-   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/consts/invalid-inline-const-in-match-arm.rs b/tests/ui/consts/invalid-inline-const-in-match-arm.rs
index 0654fd82fbc..4fe4b0d33c8 100644
--- a/tests/ui/consts/invalid-inline-const-in-match-arm.rs
+++ b/tests/ui/consts/invalid-inline-const-in-match-arm.rs
@@ -4,5 +4,6 @@ fn main() {
     match () {
         const { (|| {})() } => {}
         //~^ ERROR cannot call non-const closure in constants
+        //~| ERROR could not evaluate constant pattern
     }
 }
diff --git a/tests/ui/consts/invalid-inline-const-in-match-arm.stderr b/tests/ui/consts/invalid-inline-const-in-match-arm.stderr
index 7579f7f9692..0e41053a29d 100644
--- a/tests/ui/consts/invalid-inline-const-in-match-arm.stderr
+++ b/tests/ui/consts/invalid-inline-const-in-match-arm.stderr
@@ -11,6 +11,12 @@ help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 LL + #![feature(const_trait_impl)]
    |
 
-error: aborting due to 1 previous error
+error: could not evaluate constant pattern
+  --> $DIR/invalid-inline-const-in-match-arm.rs:5:9
+   |
+LL |         const { (|| {})() } => {}
+   |         ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0015`.
diff --git a/tests/ui/consts/issue-73976-polymorphic.stderr b/tests/ui/consts/issue-73976-polymorphic.stderr
index 97a5fbc5747..8a44eb9854f 100644
--- a/tests/ui/consts/issue-73976-polymorphic.stderr
+++ b/tests/ui/consts/issue-73976-polymorphic.stderr
@@ -1,10 +1,10 @@
-error: constant pattern depends on a generic parameter
+error[E0158]: constant pattern depends on a generic parameter
   --> $DIR/issue-73976-polymorphic.rs:20:37
    |
 LL |     matches!(GetTypeId::<T>::VALUE, GetTypeId::<T>::VALUE)
    |                                     ^^^^^^^^^^^^^^^^^^^^^
 
-error: constant pattern depends on a generic parameter
+error[E0158]: constant pattern depends on a generic parameter
   --> $DIR/issue-73976-polymorphic.rs:31:42
    |
 LL |     matches!(GetTypeNameLen::<T>::VALUE, GetTypeNameLen::<T>::VALUE)
@@ -12,3 +12,4 @@ LL |     matches!(GetTypeNameLen::<T>::VALUE, GetTypeNameLen::<T>::VALUE)
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/consts/issue-79137-toogeneric.stderr b/tests/ui/consts/issue-79137-toogeneric.stderr
index 18bdde45e2c..de81512ec6d 100644
--- a/tests/ui/consts/issue-79137-toogeneric.stderr
+++ b/tests/ui/consts/issue-79137-toogeneric.stderr
@@ -1,4 +1,4 @@
-error: constant pattern depends on a generic parameter
+error[E0158]: constant pattern depends on a generic parameter
   --> $DIR/issue-79137-toogeneric.rs:12:43
    |
 LL |     matches!(GetVariantCount::<T>::VALUE, GetVariantCount::<T>::VALUE)
@@ -6,3 +6,4 @@ LL |     matches!(GetVariantCount::<T>::VALUE, GetVariantCount::<T>::VALUE)
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/inline-const/const-match-pat-generic.stderr b/tests/ui/inline-const/const-match-pat-generic.stderr
index 15c3a876afc..26f72b34eca 100644
--- a/tests/ui/inline-const/const-match-pat-generic.stderr
+++ b/tests/ui/inline-const/const-match-pat-generic.stderr
@@ -1,10 +1,10 @@
-error: constant pattern depends on a generic parameter
+error[E0158]: constant pattern depends on a generic parameter
   --> $DIR/const-match-pat-generic.rs:7:9
    |
 LL |         const { V } => {},
    |         ^^^^^^^^^^^
 
-error: constant pattern depends on a generic parameter
+error[E0158]: constant pattern depends on a generic parameter
   --> $DIR/const-match-pat-generic.rs:19:9
    |
 LL |         const { f(V) } => {},
@@ -12,3 +12,4 @@ LL |         const { f(V) } => {},
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/pattern/issue-68393-let-pat-assoc-constant.rs b/tests/ui/pattern/issue-68393-let-pat-assoc-constant.rs
deleted file mode 100644
index 95ead6b5d4a..00000000000
--- a/tests/ui/pattern/issue-68393-let-pat-assoc-constant.rs
+++ /dev/null
@@ -1,26 +0,0 @@
-pub enum EFoo {
-    A,
-}
-
-pub trait Foo {
-    const X: EFoo;
-}
-
-struct Abc;
-
-impl Foo for Abc {
-    const X: EFoo = EFoo::A;
-}
-
-struct Def;
-impl Foo for Def {
-    const X: EFoo = EFoo::A;
-}
-
-pub fn test<A: Foo, B: Foo>(arg: EFoo, A::X: EFoo) {
-    //~^ ERROR associated consts cannot be referenced in patterns
-    let A::X = arg;
-    //~^ ERROR associated consts cannot be referenced in patterns
-}
-
-fn main() {}
diff --git a/tests/ui/pattern/issue-68393-let-pat-assoc-constant.stderr b/tests/ui/pattern/issue-68393-let-pat-assoc-constant.stderr
deleted file mode 100644
index 62c90b638d7..00000000000
--- a/tests/ui/pattern/issue-68393-let-pat-assoc-constant.stderr
+++ /dev/null
@@ -1,15 +0,0 @@
-error[E0158]: associated consts cannot be referenced in patterns
-  --> $DIR/issue-68393-let-pat-assoc-constant.rs:22:9
-   |
-LL |     let A::X = arg;
-   |         ^^^^
-
-error[E0158]: associated consts cannot be referenced in patterns
-  --> $DIR/issue-68393-let-pat-assoc-constant.rs:20:40
-   |
-LL | pub fn test<A: Foo, B: Foo>(arg: EFoo, A::X: EFoo) {
-   |                                        ^^^^
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0158`.
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.rs b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.rs
index c69fe145f77..c01f8934c75 100644
--- a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.rs
+++ b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.rs
@@ -13,7 +13,7 @@ const A: &[B] = &[];
 pub fn main() {
     match &[][..] {
         A => (),
-        //~^ ERROR must be annotated with `#[derive(PartialEq)]`
+        //~^ ERROR must implement `PartialEq`
         _ => (),
     }
 }
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.stderr b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.stderr
index 02e2bab4d0a..736e4c30c8a 100644
--- a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.stderr
+++ b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-61188-match-slice-forbidden-without-eq.stderr
@@ -1,11 +1,8 @@
-error: to use a constant of type `B` in a pattern, `B` must be annotated with `#[derive(PartialEq)]`
+error: to use a constant of type `&[B]` in a pattern, the type must implement `PartialEq`
   --> $DIR/issue-61188-match-slice-forbidden-without-eq.rs:15:9
    |
 LL |         A => (),
    |         ^
-   |
-   = note: the traits must be derived, manual `impl`s are not sufficient
-   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.rs b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.rs
index 6d6a336e688..f343013f2b0 100644
--- a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.rs
+++ b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.rs
@@ -28,13 +28,9 @@ fn main() {
     // Also cover range patterns
     match x {
         NAN..=1.0 => {}, //~ ERROR cannot use NaN in patterns
-        //~^ ERROR lower range bound must be less than or equal to upper
         -1.0..=NAN => {}, //~ ERROR cannot use NaN in patterns
-        //~^ ERROR lower range bound must be less than or equal to upper
         NAN.. => {}, //~ ERROR cannot use NaN in patterns
-        //~^ ERROR lower range bound must be less than or equal to upper
         ..NAN => {}, //~ ERROR cannot use NaN in patterns
-        //~^ ERROR lower range bound must be less than upper
         _ => {},
     };
 }
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.stderr b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.stderr
index baca1d75048..44b05ea31e9 100644
--- a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.stderr
+++ b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-6804-nan-match.stderr
@@ -34,14 +34,8 @@ LL |         NAN..=1.0 => {},
    = note: NaNs compare inequal to everything, even themselves, so this pattern would never match
    = help: try using the `is_nan` method instead
 
-error[E0030]: lower range bound must be less than or equal to upper
-  --> $DIR/issue-6804-nan-match.rs:30:9
-   |
-LL |         NAN..=1.0 => {},
-   |         ^^^^^^^^^ lower bound larger than upper bound
-
 error: cannot use NaN in patterns
-  --> $DIR/issue-6804-nan-match.rs:32:16
+  --> $DIR/issue-6804-nan-match.rs:31:16
    |
 LL |         -1.0..=NAN => {},
    |                ^^^
@@ -49,14 +43,8 @@ LL |         -1.0..=NAN => {},
    = note: NaNs compare inequal to everything, even themselves, so this pattern would never match
    = help: try using the `is_nan` method instead
 
-error[E0030]: lower range bound must be less than or equal to upper
-  --> $DIR/issue-6804-nan-match.rs:32:9
-   |
-LL |         -1.0..=NAN => {},
-   |         ^^^^^^^^^^ lower bound larger than upper bound
-
 error: cannot use NaN in patterns
-  --> $DIR/issue-6804-nan-match.rs:34:9
+  --> $DIR/issue-6804-nan-match.rs:32:9
    |
 LL |         NAN.. => {},
    |         ^^^
@@ -64,14 +52,8 @@ LL |         NAN.. => {},
    = note: NaNs compare inequal to everything, even themselves, so this pattern would never match
    = help: try using the `is_nan` method instead
 
-error[E0030]: lower range bound must be less than or equal to upper
-  --> $DIR/issue-6804-nan-match.rs:34:9
-   |
-LL |         NAN.. => {},
-   |         ^^^^^ lower bound larger than upper bound
-
 error: cannot use NaN in patterns
-  --> $DIR/issue-6804-nan-match.rs:36:11
+  --> $DIR/issue-6804-nan-match.rs:33:11
    |
 LL |         ..NAN => {},
    |           ^^^
@@ -79,13 +61,5 @@ LL |         ..NAN => {},
    = note: NaNs compare inequal to everything, even themselves, so this pattern would never match
    = help: try using the `is_nan` method instead
 
-error[E0579]: lower range bound must be less than upper
-  --> $DIR/issue-6804-nan-match.rs:36:9
-   |
-LL |         ..NAN => {},
-   |         ^^^^^
-
-error: aborting due to 11 previous errors
+error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0030, E0579.
-For more information about an error, try `rustc --explain E0030`.