Auto merge of #74113 - lcnr:type-dependent-consts-2, r=eddyb

Support const args in type dependent paths (Take 2)

once more, except it is sound this time :smiling_face_with_three_hearts: previously #71154

-----
```rust
#![feature(const_generics)]

struct A;
impl A {
    fn foo<const N: usize>(&self) -> usize { N }
}
struct B;
impl B {
    fn foo<const N: usize>(&self) -> usize { 42 }
}

fn main() {
    let a = A;
    a.foo::<7>();
}
```
When calling `type_of` for generic const arguments, we now use the `TypeckTables` of the surrounding body to get the expected type.

This alone causes cycle errors though, as we now have `typeck_tables_of(main)` -> `...` ->
`type_of(main_ANON0 := 7)` -> `typeck_tables_of(main)` :zap: (see https://github.com/rust-lang/rust/issues/68400#issuecomment-611760290)

To prevent this we must not call `type_of(const_arg)` during `typeck_tables_of`. This is achieved by
calling `type_of(param_def_id)` instead.

We have to somehow remember the `DefId` of the param through all of typeck, which is done using the
struct `ty::WithOptConstParam<DefId>`, which replaces `DefId` where needed and contains an `Option<DefId>` to
be able to store the const parameter in case it exists.

Queries which are currently cached on disk are split into two variants: `query_name`(cached) and `query_name_(of|for)_const_arg`(not cached), with `query_name_of_const_arg` taking a pair `(did, param_did): (LocalDefId, DefId)`.

For some queries a method `query_name_of_opt_const_arg` is added to `TyCtxt` which takes a `ty::WithOptConstParam` and either calls `query_name` or `query_name_of_const_arg` depending on the value of `const_param_did`.

r? @eddyb @varkor

1 files changed, 4 insertions, 4 deletions

diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index 832b2420c23..52c30668826 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -466,12 +466,12 @@ pub fn name_from_pat(p: &hir::Pat<'_>) -> String {
 
 pub fn print_const(cx: &DocContext<'_>, n: &'tcx ty::Const<'_>) -> String {
     match n.val {
-        ty::ConstKind::Unevaluated(def_id, _, promoted) => {
-            let mut s = if let Some(def_id) = def_id.as_local() {
-                let hir_id = cx.tcx.hir().as_local_hir_id(def_id);
+        ty::ConstKind::Unevaluated(def, _, promoted) => {
+            let mut s = if let Some(def) = def.as_local() {
+                let hir_id = cx.tcx.hir().as_local_hir_id(def.did);
                 print_const_expr(cx, cx.tcx.hir().body_owned_by(hir_id))
             } else {
-                inline::print_inlined_const(cx, def_id)
+                inline::print_inlined_const(cx, def.did)
             };
             if let Some(promoted) = promoted {
                 s.push_str(&format!("::{:?}", promoted))