Rollup merge of rust-lang#106873 - BoxyUwU:ty_const_formatting, r=compiler-errors

dont randomly use `_` to print out const generic arguments

const generics seem to get printed out as `_` for no reason a lot of the time, as someone who spends a lot of time with const generics this has gotten ✨ very annoying ✨. Latest example would be rust-lang#106423 where the ICE messaged formatted a `ty::Const` containing no infer vars, as `_`.

For some reason printing of the const argument on arrays was custom instead of using the existing logic for printing `ty::Const`. Additionally the existing logic for printing `ty::Const` would print out `_` for anon consts that are in a separate crate leading to weird diagnostics (see second commit). There ought to be less cases of consts randomly getting printed as `_` hiding valuable info now.

Author: matthiaskrgr

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -854,24 +854,7 @@ pub trait PrettyPrinter<'tcx>:
                 }
                 p!("]");
             }
-            ty::Array(ty, sz) => {
-                p!("[", print(ty), "; ");
-                if self.should_print_verbose() {
-                    p!(write("{:?}", sz));
-                } else if let ty::ConstKind::Unevaluated(..) = sz.kind() {
-                    // Do not try to evaluate unevaluated constants. If we are const evaluating an
-                    // array length anon const, rustc will (with debug assertions) print the
-                    // constant's path. Which will end up here again.
-                    p!("_");
-                } else if let Some(n) = sz.kind().try_to_bits(self.tcx().data_layout.pointer_size) {
-                    p!(write("{}", n));
-                } else if let ty::ConstKind::Param(param) = sz.kind() {
-                    p!(print(param));
-                } else {
-                    p!("_");
-                }
-                p!("]")
-            }
+            ty::Array(ty, sz) => p!("[", print(ty), "; ", print(sz), "]"),
             ty::Slice(ty) => p!("[", print(ty), "]"),
         }
 
@@ -1303,21 +1286,25 @@ pub trait PrettyPrinter<'tcx>:
         match ct.kind() {
             ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => {
                 match self.tcx().def_kind(def.did) {
-                    DefKind::Static(..) | DefKind::Const | DefKind::AssocConst => {
+                    DefKind::Const | DefKind::AssocConst => {
                         p!(print_value_path(def.did, substs))
                     }
-                    _ => {
-                        if def.is_local() {
-                            let span = self.tcx().def_span(def.did);
-                            if let Ok(snip) = self.tcx().sess.source_map().span_to_snippet(span) {
-                                p!(write("{}", snip))
-                            } else {
-                                print_underscore!()
-                            }
+                    DefKind::AnonConst => {
+                        if def.is_local()
+                            && let span = self.tcx().def_span(def.did)
+                            && let Ok(snip) = self.tcx().sess.source_map().span_to_snippet(span)
+                        {
+                            p!(write("{}", snip))
                         } else {
-                            print_underscore!()
+                            // Do not call `print_value_path` as if a parent of this anon const is an impl it will
+                            // attempt to print out the impl trait ref i.e. `<T as Trait>::{constant#0}`. This would
+                            // cause printing to enter an infinite recursion if the anon const is in the self type i.e.
+                            // `impl<T: Default> Default for [T; 32 - 1 - 1 - 1] {`
+                            // where we would try to print `<[T; /* print `constant#0` again */] as Default>::{constant#0}`
+                            p!(write("{}::{}", self.tcx().crate_name(def.did.krate), self.tcx().def_path(def.did).to_string_no_crate_verbose()))
                         }
                     }
+                    defkind => bug!("`{:?}` has unexpcted defkind {:?}", ct, defkind),
                 }
             }
             ty::ConstKind::Infer(infer_ct) => {
@@ -1339,7 +1326,7 @@ pub trait PrettyPrinter<'tcx>:
             ty::ConstKind::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
             // FIXME(generic_const_exprs):
             // write out some legible representation of an abstract const?
-            ty::ConstKind::Expr(_) => p!("[Const Expr]"),
+            ty::ConstKind::Expr(_) => p!("[const expr]"),
             ty::ConstKind::Error(_) => p!("[const error]"),
         };
         Ok(self)

tests/mir-opt/nll/region_subtyping_basic.main.nll.0.32bit.mir

@@ -22,7 +22,7 @@
 |
 fn main() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/region_subtyping_basic.rs:+0:11: +0:11
-    let mut _1: [usize; Const { ty: usize, kind: Value(Leaf(0x00000003)) }]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
+    let mut _1: [usize; Const(Value(Leaf(0x00000003)): usize)]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
     let _3: usize;                       // in scope 0 at $DIR/region_subtyping_basic.rs:+2:16: +2:17
     let mut _4: usize;                   // in scope 0 at $DIR/region_subtyping_basic.rs:+2:14: +2:18
     let mut _5: bool;                    // in scope 0 at $DIR/region_subtyping_basic.rs:+2:14: +2:18

tests/mir-opt/nll/region_subtyping_basic.main.nll.0.64bit.mir

@@ -22,7 +22,7 @@
 |
 fn main() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/region_subtyping_basic.rs:+0:11: +0:11
-    let mut _1: [usize; Const { ty: usize, kind: Value(Leaf(0x0000000000000003)) }]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
+    let mut _1: [usize; Const(Value(Leaf(0x0000000000000003)): usize)]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
     let _3: usize;                       // in scope 0 at $DIR/region_subtyping_basic.rs:+2:16: +2:17
     let mut _4: usize;                   // in scope 0 at $DIR/region_subtyping_basic.rs:+2:14: +2:18
     let mut _5: bool;                    // in scope 0 at $DIR/region_subtyping_basic.rs:+2:14: +2:18

tests/ui/const-generics/const-param-type-depends-on-const-param.min.stderr

@@ -10,7 +10,7 @@ error[E0770]: the type of const parameters must not depend on other generic para
 LL | pub struct SelfDependent<const N: [u8; N]>;
    |                                        ^ the type must not depend on the parameter `N`
 
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; N]` is forbidden as the type of a const generic parameter
   --> $DIR/const-param-type-depends-on-const-param.rs:11:47
    |
 LL | pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
@@ -19,7 +19,7 @@ LL | pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
    = note: the only supported types are integers, `bool` and `char`
    = help: more complex types are supported with `#![feature(adt_const_params)]`
 
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; N]` is forbidden as the type of a const generic parameter
   --> $DIR/const-param-type-depends-on-const-param.rs:15:35
    |
 LL | pub struct SelfDependent<const N: [u8; N]>;

tests/ui/const-generics/const-param-type-depends-on-const-param.rs

@@ -10,10 +10,10 @@
 
 pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
 //~^ ERROR: the type of const parameters must not depend on other generic parameters
-//[min]~^^ ERROR `[u8; _]` is forbidden
+//[min]~^^ ERROR `[u8; N]` is forbidden
 
 pub struct SelfDependent<const N: [u8; N]>;
 //~^ ERROR: the type of const parameters must not depend on other generic parameters
-//[min]~^^ ERROR `[u8; _]` is forbidden
+//[min]~^^ ERROR `[u8; N]` is forbidden
 
 fn main() {}

tests/ui/const-generics/dont-evaluate-array-len-on-err-1.stderr

@@ -1,8 +1,8 @@
-error[E0277]: the trait bound `[Adt; _]: Foo` is not satisfied
+error[E0277]: the trait bound `[Adt; std::mem::size_of::<Self::Assoc>()]: Foo` is not satisfied
   --> $DIR/dont-evaluate-array-len-on-err-1.rs:15:9
    |
 LL |         <[Adt; std::mem::size_of::<Self::Assoc>()] as Foo>::bar()
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `[Adt; _]`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `[Adt; std::mem::size_of::<Self::Assoc>()]`
 
 error: aborting due to previous error
 

tests/ui/const-generics/generic_const_exprs/auxiliary/anon_const_non_local.rs

@@ -0,0 +1,8 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+pub struct Foo<const N: usize>;
+
+pub fn foo<const N: usize>() -> Foo<{ N + 1 }> {
+    Foo
+}

tests/ui/const-generics/generic_const_exprs/issue-62504.min.stderr

@@ -15,7 +15,7 @@ LL |         ArrayHolder([0; Self::SIZE])
    |         arguments to this struct are incorrect
    |
    = note: expected array `[u32; X]`
-              found array `[u32; _]`
+              found array `[u32; Self::SIZE]`
 note: tuple struct defined here
   --> $DIR/issue-62504.rs:14:8
    |

tests/ui/const-generics/generic_const_exprs/issue-79518-default_trait_method_normalization.stderr

@@ -2,13 +2,13 @@ error[E0308]: mismatched types
   --> $DIR/issue-79518-default_trait_method_normalization.rs:16:32
    |
 LL |         Self::AssocInstance == [(); std::mem::size_of::<Self::Assoc>()];
-   |         -------------------    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected associated type, found array `[(); _]`
+   |         -------------------    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected associated type, found array `[(); std::mem::size_of::<Self::Assoc>()]`
    |         |
    |         expected because this is `<Self as Foo>::Assoc`
    |
    = note: expected associated type `<Self as Foo>::Assoc`
-                        found array `[(); _]`
-   = help: consider constraining the associated type `<Self as Foo>::Assoc` to `[(); _]` or calling a method that returns `<Self as Foo>::Assoc`
+                        found array `[(); std::mem::size_of::<Self::Assoc>()]`
+   = help: consider constraining the associated type `<Self as Foo>::Assoc` to `[(); std::mem::size_of::<Self::Assoc>()]` or calling a method that returns `<Self as Foo>::Assoc`
    = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
 
 error: aborting due to previous error

tests/ui/const-generics/generic_const_exprs/non_local_anon_const_diagnostics.rs

@@ -0,0 +1,16 @@
+// aux-build:anon_const_non_local.rs
+
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+extern crate anon_const_non_local;
+
+fn bar<const M: usize>()
+where
+    [(); M + 1]:,
+{
+    let _: anon_const_non_local::Foo<2> = anon_const_non_local::foo::<M>();
+    //~^ ERROR: mismatched types
+}
+
+fn main() {}

tests/ui/const-generics/generic_const_exprs/non_local_anon_const_diagnostics.stderr

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/non_local_anon_const_diagnostics.rs:12:43
+   |
+LL |     let _: anon_const_non_local::Foo<2> = anon_const_non_local::foo::<M>();
+   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `2`, found `anon_const_non_local::::foo::{constant#0}`
+   |
+   = note: expected constant `2`
+              found constant `anon_const_non_local::::foo::{constant#0}`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/issues/issue-62878.min.stderr

@@ -4,7 +4,7 @@ error[E0770]: the type of const parameters must not depend on other generic para
 LL | fn foo<const N: usize, const A: [u8; N]>() {}
    |                                      ^ the type must not depend on the parameter `N`
 
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; N]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-62878.rs:5:33
    |
 LL | fn foo<const N: usize, const A: [u8; N]>() {}

tests/ui/const-generics/issues/issue-62878.rs

@@ -4,7 +4,7 @@
 
 fn foo<const N: usize, const A: [u8; N]>() {}
 //~^ ERROR the type of const parameters must not
-//[min]~| ERROR `[u8; _]` is forbidden as the type of a const generic parameter
+//[min]~| ERROR `[u8; N]` is forbidden as the type of a const generic parameter
 
 fn main() {
     foo::<_, { [1] }>();

tests/ui/const-generics/issues/issue-71169.min.stderr

@@ -4,7 +4,7 @@ error[E0770]: the type of const parameters must not depend on other generic para
 LL | fn foo<const LEN: usize, const DATA: [u8; LEN]>() {}
    |                                           ^^^ the type must not depend on the parameter `LEN`
 
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; LEN]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-71169.rs:5:38
    |
 LL | fn foo<const LEN: usize, const DATA: [u8; LEN]>() {}

tests/ui/const-generics/issues/issue-71169.rs

@@ -4,7 +4,7 @@
 
 fn foo<const LEN: usize, const DATA: [u8; LEN]>() {}
 //~^ ERROR the type of const parameters must not
-//[min]~^^ ERROR `[u8; _]` is forbidden as the type of a const generic parameter
+//[min]~^^ ERROR `[u8; LEN]` is forbidden as the type of a const generic parameter
 fn main() {
     const DATA: [u8; 4] = *b"ABCD";
     foo::<4, DATA>();

tests/ui/const-generics/issues/issue-73491.min.stderr

@@ -1,4 +1,4 @@
-error: `[u32; _]` is forbidden as the type of a const generic parameter
+error: `[u32; LEN]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-73491.rs:8:19
    |
 LL | fn hoge<const IN: [u32; LEN]>() {}

tests/ui/const-generics/issues/issue-73491.rs

@@ -6,6 +6,6 @@
 const LEN: usize = 1024;
 
 fn hoge<const IN: [u32; LEN]>() {}
-//[min]~^ ERROR `[u32; _]` is forbidden as the type of a const generic parameter
+//[min]~^ ERROR `[u32; LEN]` is forbidden as the type of a const generic parameter
 
 fn main() {}

tests/ui/const-generics/issues/issue-74101.min.stderr

@@ -1,4 +1,4 @@
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; 1 + 2]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-74101.rs:6:18
    |
 LL | fn test<const N: [u8; 1 + 2]>() {}
@@ -7,7 +7,7 @@ LL | fn test<const N: [u8; 1 + 2]>() {}
    = note: the only supported types are integers, `bool` and `char`
    = help: more complex types are supported with `#![feature(adt_const_params)]`
 
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; 1 + 2]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-74101.rs:9:21
    |
 LL | struct Foo<const N: [u8; 1 + 2]>;

tests/ui/const-generics/issues/issue-74101.rs

@@ -4,9 +4,9 @@
 #![cfg_attr(full, allow(incomplete_features))]
 
 fn test<const N: [u8; 1 + 2]>() {}
-//[min]~^ ERROR `[u8; _]` is forbidden as the type of a const generic parameter
+//[min]~^ ERROR `[u8; 1 + 2]` is forbidden as the type of a const generic parameter
 
 struct Foo<const N: [u8; 1 + 2]>;
-//[min]~^ ERROR `[u8; _]` is forbidden as the type of a const generic parameter
+//[min]~^ ERROR `[u8; 1 + 2]` is forbidden as the type of a const generic parameter
 
 fn main() {}

tests/ui/const-generics/issues/issue-75047.min.stderr

@@ -1,4 +1,4 @@
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; Bar::<u32>::value()]` is forbidden as the type of a const generic parameter
   --> $DIR/issue-75047.rs:14:21
    |
 LL | struct Foo<const N: [u8; Bar::<u32>::value()]>;

tests/ui/const-generics/issues/issue-75047.rs

@@ -12,6 +12,6 @@ impl<T> Bar<T> {
 }
 
 struct Foo<const N: [u8; Bar::<u32>::value()]>;
-//[min]~^ ERROR `[u8; _]` is forbidden as the type of a const generic parameter
+//[min]~^ ERROR `[u8; Bar::<u32>::value()]` is forbidden as the type of a const generic parameter
 
 fn main() {}

tests/ui/const-generics/nested-type.min.stderr

@@ -1,4 +1,14 @@
-error: `[u8; _]` is forbidden as the type of a const generic parameter
+error: `[u8; {
+           struct Foo<const N: usize>;
+       
+           impl<const N: usize> Foo<N> {
+               fn value() -> usize {
+                   N
+               }
+           }
+       
+           Foo::<17>::value()
+       }]` is forbidden as the type of a const generic parameter
   --> $DIR/nested-type.rs:6:21
    |
 LL |   struct Foo<const N: [u8; {

tests/ui/consts/const-size_of-cycle.stderr

@@ -15,8 +15,8 @@ note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`..
 LL |     bytes: [u8; std::mem::size_of::<Foo>()]
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Foo`...
-   = note: ...which requires computing layout of `[u8; _]`...
-   = note: ...which requires normalizing `[u8; _]`...
+   = note: ...which requires computing layout of `[u8; std::mem::size_of::<Foo>()]`...
+   = note: ...which requires normalizing `[u8; std::mem::size_of::<Foo>()]`...
    = note: ...which again requires evaluating type-level constant, completing the cycle
 note: cycle used when checking that `Foo` is well-formed
   --> $DIR/const-size_of-cycle.rs:3:1

tests/ui/consts/issue-44415.stderr

@@ -15,8 +15,8 @@ note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`..
 LL |     bytes: [u8; unsafe { intrinsics::size_of::<Foo>() }],
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Foo`...
-   = note: ...which requires computing layout of `[u8; _]`...
-   = note: ...which requires normalizing `[u8; _]`...
+   = note: ...which requires computing layout of `[u8; unsafe { intrinsics::size_of::<Foo>() }]`...
+   = note: ...which requires normalizing `[u8; unsafe { intrinsics::size_of::<Foo>() }]`...
    = note: ...which again requires evaluating type-level constant, completing the cycle
 note: cycle used when checking that `Foo` is well-formed
   --> $DIR/issue-44415.rs:5:1

tests/ui/consts/too_generic_eval_ice.rs

@@ -7,7 +7,7 @@ impl<A, B> Foo<A, B> {
         [5; Self::HOST_SIZE] == [6; 0]
         //~^ ERROR constant expression depends on a generic parameter
         //~| ERROR constant expression depends on a generic parameter
-        //~| ERROR can't compare `[{integer}; _]` with `[{integer}; 0]`
+        //~| ERROR can't compare `[{integer}; Self::HOST_SIZE]` with `[{integer}; 0]`
     }
 }
 

tests/ui/consts/too_generic_eval_ice.stderr

@@ -14,13 +14,13 @@ LL |         [5; Self::HOST_SIZE] == [6; 0]
    |
    = note: this may fail depending on what value the parameter takes
 
-error[E0277]: can't compare `[{integer}; _]` with `[{integer}; 0]`
+error[E0277]: can't compare `[{integer}; Self::HOST_SIZE]` with `[{integer}; 0]`
   --> $DIR/too_generic_eval_ice.rs:7:30
    |
 LL |         [5; Self::HOST_SIZE] == [6; 0]
-   |                              ^^ no implementation for `[{integer}; _] == [{integer}; 0]`
+   |                              ^^ no implementation for `[{integer}; Self::HOST_SIZE] == [{integer}; 0]`
    |
-   = help: the trait `PartialEq<[{integer}; 0]>` is not implemented for `[{integer}; _]`
+   = help: the trait `PartialEq<[{integer}; 0]>` is not implemented for `[{integer}; Self::HOST_SIZE]`
    = help: the following other types implement trait `PartialEq<Rhs>`:
              <&[B] as PartialEq<[A; N]>>
              <&[T] as PartialEq<Vec<U, A>>>

tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-1.stderr

@@ -1,4 +1,4 @@
-error: values of the type `[u8; SIZE]` are too big for the current architecture
+error: values of the type `[u8; usize::MAX]` are too big for the current architecture
 
 error: aborting due to previous error
 

tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.stderr

@@ -1,4 +1,4 @@
-error: values of the type `[u8; SIZE]` are too big for the current architecture
+error: values of the type `[u8; usize::MAX]` are too big for the current architecture
 
 error: aborting due to previous error
 

tests/ui/inference/issue-83606.rs

@@ -6,5 +6,5 @@ fn foo<const N: usize>(_: impl std::fmt::Display) -> [usize; N] {
 
 fn main() {
     let _ = foo("foo");
-    //~^ ERROR: type annotations needed for `[usize; _]`
+    //~^ ERROR: type annotations needed for `[usize; N]`
 }

tests/ui/inference/issue-83606.stderr

@@ -1,12 +1,12 @@
-error[E0282]: type annotations needed for `[usize; _]`
+error[E0282]: type annotations needed for `[usize; N]`
   --> $DIR/issue-83606.rs:8:9
    |
 LL |     let _ = foo("foo");
    |         ^
    |
 help: consider giving this pattern a type, where the the value of const parameter `N` is specified
    |
-LL |     let _: [usize; _] = foo("foo");
+LL |     let _: [usize; N] = foo("foo");
    |          ++++++++++++
 
 error: aborting due to previous error

tests/ui/limits/issue-15919-32.stderr

@@ -1,4 +1,4 @@
-error: values of the type `[usize; 4294967295]` are too big for the current architecture
+error: values of the type `[usize; usize::MAX]` are too big for the current architecture
   --> $DIR/issue-15919-32.rs:9:9
    |
 LL |     let x = [0usize; 0xffff_ffff];

tests/ui/limits/issue-15919-64.stderr

@@ -1,4 +1,4 @@
-error: values of the type `[usize; 18446744073709551615]` are too big for the current architecture
+error: values of the type `[usize; usize::MAX]` are too big for the current architecture
   --> $DIR/issue-15919-64.rs:9:9
    |
 LL |     let x = [0usize; 0xffff_ffff_ffff_ffff];