Auto merge of #111630 - BoxyUwU:ty_const_debug_formatting, r=compiler-errors

debug format `Const`'s less verbosely

Not user visible change only visible to people debugging const generics.

Currently debug output for `ty::Const` is super verbose (even for `-Zverbose` lol), things like printing infer vars as `Infer(Var(?0c))` instead of just `?0c`, bound vars and placeholders not using `^0_1` or `!0_1` syntax respectively. With these changes its imo better but not perfect:
`Const { ty: usize, kind: ^0_1 }`
is still a lot for not much information. not entirely sure what to do about that so not dealing with it yet.

Need to do formatting for `ConstKind::Expr` at some point too since rn it sucks (doesn't even print anything with `Display`) not gonna do that in this PR either.

r? `@compiler-errors`

7 files changed, 75 insertions, 45 deletions

diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index 0a5792a9c47..1a4bd14815f 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -6,7 +6,6 @@ use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::LocalDefId;
 use rustc_macros::HashStable;
-use std::fmt;
 
 mod int;
 mod kind;
@@ -21,15 +20,6 @@ pub use valtree::*;
 #[rustc_pass_by_value]
 pub struct Const<'tcx>(pub(super) Interned<'tcx, ConstData<'tcx>>);
 
-impl<'tcx> fmt::Debug for Const<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        // This reflects what `Const` looked liked before `Interned` was
-        // introduced. We print it like this to avoid having to update expected
-        // output in a lot of tests.
-        write!(f, "Const {{ ty: {:?}, kind: {:?} }}", self.ty(), self.kind())
-    }
-}
-
 /// Typed constant value.
 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
 pub struct ConstData<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/consts/kind.rs b/compiler/rustc_middle/src/ty/consts/kind.rs
index a108f6c8947..1dd4f8a2437 100644
--- a/compiler/rustc_middle/src/ty/consts/kind.rs
+++ b/compiler/rustc_middle/src/ty/consts/kind.rs
@@ -42,7 +42,7 @@ impl<'tcx> UnevaluatedConst<'tcx> {
 }
 
 /// Represents a constant in Rust.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
+#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
 #[derive(Hash, HashStable, TypeFoldable, TypeVisitable)]
 #[derive(derive_more::From)]
 pub enum ConstKind<'tcx> {
@@ -128,7 +128,7 @@ impl<'tcx> ConstKind<'tcx> {
 }
 
 /// An inference variable for a const, for use in const generics.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Hash)]
+#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Hash)]
 pub enum InferConst<'tcx> {
     /// Infer the value of the const.
     Var(ty::ConstVid<'tcx>),
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 385156262c7..a8193c3e559 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -703,7 +703,7 @@ pub trait PrettyPrinter<'tcx>:
             ty::Error(_) => p!("[type error]"),
             ty::Param(ref param_ty) => p!(print(param_ty)),
             ty::Bound(debruijn, bound_ty) => match bound_ty.kind {
-                ty::BoundTyKind::Anon => self.pretty_print_bound_var(debruijn, bound_ty.var)?,
+                ty::BoundTyKind::Anon => debug_bound_var(&mut self, debruijn, bound_ty.var)?,
                 ty::BoundTyKind::Param(_, s) => match self.should_print_verbose() {
                     true if debruijn == ty::INNERMOST => p!(write("^{}", s)),
                     true => p!(write("^{}_{}", debruijn.index(), s)),
@@ -741,7 +741,7 @@ pub trait PrettyPrinter<'tcx>:
             }
             ty::Placeholder(placeholder) => match placeholder.bound.kind {
                 ty::BoundTyKind::Anon => {
-                    self.pretty_print_placeholder_var(placeholder.universe, placeholder.bound.var)?
+                    debug_placeholder_var(&mut self, placeholder.universe, placeholder.bound.var)?;
                 }
                 ty::BoundTyKind::Param(_, name) => p!(write("{}", name)),
             },
@@ -1164,30 +1164,6 @@ pub trait PrettyPrinter<'tcx>:
         traits.entry(trait_ref).or_default().extend(proj_ty);
     }
 
-    fn pretty_print_bound_var(
-        &mut self,
-        debruijn: ty::DebruijnIndex,
-        var: ty::BoundVar,
-    ) -> Result<(), Self::Error> {
-        if debruijn == ty::INNERMOST {
-            write!(self, "^{}", var.index())
-        } else {
-            write!(self, "^{}_{}", debruijn.index(), var.index())
-        }
-    }
-
-    fn pretty_print_placeholder_var(
-        &mut self,
-        ui: ty::UniverseIndex,
-        var: ty::BoundVar,
-    ) -> Result<(), Self::Error> {
-        if ui == ty::UniverseIndex::ROOT {
-            write!(self, "!{}", var.index())
-        } else {
-            write!(self, "!{}_{}", ui.index(), var.index())
-        }
-    }
-
     fn ty_infer_name(&self, _: ty::TyVid) -> Option<Symbol> {
         None
     }
@@ -1321,7 +1297,7 @@ pub trait PrettyPrinter<'tcx>:
         define_scoped_cx!(self);
 
         if self.should_print_verbose() {
-            p!(write("Const({:?}: {:?})", ct.kind(), ct.ty()));
+            p!(write("{:?}", ct));
             return Ok(self);
         }
 
@@ -1380,9 +1356,11 @@ pub trait PrettyPrinter<'tcx>:
             }
 
             ty::ConstKind::Bound(debruijn, bound_var) => {
-                self.pretty_print_bound_var(debruijn, bound_var)?
+                debug_bound_var(&mut self, debruijn, bound_var)?
             }
-            ty::ConstKind::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
+            ty::ConstKind::Placeholder(placeholder) => {
+                debug_placeholder_var(&mut self, placeholder.universe, placeholder.bound)?;
+            },
             // FIXME(generic_const_exprs):
             // write out some legible representation of an abstract const?
             ty::ConstKind::Expr(_) => p!("[const expr]"),
@@ -3067,3 +3045,27 @@ pub struct OpaqueFnEntry<'tcx> {
     fn_trait_ref: Option<ty::PolyTraitRef<'tcx>>,
     return_ty: Option<ty::Binder<'tcx, Term<'tcx>>>,
 }
+
+pub fn debug_bound_var<T: std::fmt::Write>(
+    fmt: &mut T,
+    debruijn: ty::DebruijnIndex,
+    var: ty::BoundVar,
+) -> Result<(), std::fmt::Error> {
+    if debruijn == ty::INNERMOST {
+        write!(fmt, "^{}", var.index())
+    } else {
+        write!(fmt, "^{}_{}", debruijn.index(), var.index())
+    }
+}
+
+pub fn debug_placeholder_var<T: std::fmt::Write>(
+    fmt: &mut T,
+    universe: ty::UniverseIndex,
+    bound: ty::BoundVar,
+) -> Result<(), std::fmt::Error> {
+    if universe == ty::UniverseIndex::ROOT {
+        write!(fmt, "!{}", bound.index())
+    } else {
+        write!(fmt, "!{}_{}", universe.index(), bound.index())
+    }
+}
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index e73208b877f..16cb6c91046 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -192,6 +192,44 @@ impl<'tcx> fmt::Debug for AliasTy<'tcx> {
     }
 }
 
+impl<'tcx> fmt::Debug for ty::InferConst<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            InferConst::Var(var) => write!(f, "{var:?}"),
+            InferConst::Fresh(var) => write!(f, "Fresh({var:?})"),
+        }
+    }
+}
+
+impl<'tcx> fmt::Debug for ty::Const<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // This reflects what `Const` looked liked before `Interned` was
+        // introduced. We print it like this to avoid having to update expected
+        // output in a lot of tests.
+        write!(f, "Const {{ ty: {:?}, kind: {:?} }}", self.ty(), self.kind())
+    }
+}
+
+impl<'tcx> fmt::Debug for ty::ConstKind<'tcx> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use ty::ConstKind::*;
+        match self {
+            Param(param) => write!(f, "{param:?}"),
+            Infer(var) => write!(f, "{var:?}"),
+            Bound(debruijn, var) => ty::print::debug_bound_var(f, *debruijn, *var),
+            Placeholder(placeholder) => {
+                ty::print::debug_placeholder_var(f, placeholder.universe, placeholder.bound)
+            }
+            Unevaluated(uv) => {
+                f.debug_tuple("Unevaluated").field(&uv.substs).field(&uv.def).finish()
+            }
+            Value(valtree) => write!(f, "{valtree:?}"),
+            Error(_) => write!(f, "[const error]"),
+            Expr(expr) => write!(f, "{expr:?}"),
+        }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // Atomic structs
 //
diff --git a/tests/mir-opt/issue_99325.main.built.after.mir b/tests/mir-opt/issue_99325.main.built.after.mir
index f0c9ef419bd..0424ce3abeb 100644
--- a/tests/mir-opt/issue_99325.main.built.after.mir
+++ b/tests/mir-opt/issue_99325.main.built.after.mir
@@ -1,8 +1,8 @@
 // MIR for `main` after built
 
 | User Type Annotations
-| 0: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[22bb]::function_with_bytes), UserSubsts { substs: [Const { ty: &'static [u8; 4], kind: Value(Branch([Leaf(0x41), Leaf(0x41), Leaf(0x41), Leaf(0x41)])) }], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:10:16: 10:46, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}
-| 1: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[22bb]::function_with_bytes), UserSubsts { substs: [Const { ty: &'static [u8; 4], kind: Unevaluated(UnevaluatedConst { def: DefId(0:8 ~ issue_99325[22bb]::main::{constant#1}), substs: [] }) }], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:11:16: 11:68, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}
+| 0: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[22bb]::function_with_bytes), UserSubsts { substs: [Const { ty: &'static [u8; 4], kind: Branch([Leaf(0x41), Leaf(0x41), Leaf(0x41), Leaf(0x41)]) }], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:10:16: 10:46, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}
+| 1: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[22bb]::function_with_bytes), UserSubsts { substs: [Const { ty: &'static [u8; 4], kind: Unevaluated([], DefId(0:8 ~ issue_99325[22bb]::main::{constant#1})) }], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:11:16: 11:68, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}
 |
 fn main() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/issue_99325.rs:+0:15: +0:15
diff --git a/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.32bit.mir b/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.32bit.mir
index 71bdfcc5c49..c425f3cd506 100644
--- a/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.32bit.mir
+++ b/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(Value(Leaf(0x00000003)): usize)]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
+    let mut _1: [usize; Const { ty: usize, kind: Leaf(0x00000003) }]; // 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
diff --git a/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.64bit.mir b/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.64bit.mir
index 9fa8609b751..22ad24f8d77 100644
--- a/tests/mir-opt/nll/region_subtyping_basic.main.nll.0.64bit.mir
+++ b/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(Value(Leaf(0x0000000000000003)): usize)]; // in scope 0 at $DIR/region_subtyping_basic.rs:+1:9: +1:14
+    let mut _1: [usize; Const { ty: usize, kind: Leaf(0x0000000000000003) }]; // 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