Remove hook calling via TyCtxtAt.

All hooks receive a `TyCtxtAt` argument.

Currently hooks can be called through `TyCtxtAt` or `TyCtxt`. In the
latter case, a `TyCtxtAt` is constructed with a dummy span and passed to
the hook.

However, in practice hooks are never called through `TyCtxtAt`, and
always receive a dummy span. (I confirmed this via code inspection, and
double-checked it by temporarily making the `TyCtxtAt` code path panic
and running all the tests.)

This commit removes all the `TyCtxtAt` machinery for hooks. All hooks
now receive `TyCtxt` instead of `TyCtxtAt`. There are two existing hooks
that use `TyCtxtAt::span`: `const_caller_location_provider` and
`try_destructure_mir_constant_for_user_output`. For both hooks the span
is always a dummy span, probably unintentionally. This dummy span use is
now explicit. If a non-dummy span is needed for these two hooks it would
be easy to add it as an extra argument because hooks are less
constrained than queries.

compiler/rustc_const_eval/src/const_eval/mod.rs

@@ -1,7 +1,7 @@
 // Not in interpret to make sure we do not use private implementation details
 
 use rustc_abi::VariantIdx;
-use rustc_middle::query::{Key, TyCtxtAt};
+use rustc_middle::query::Key;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::{bug, mir};
@@ -35,16 +35,17 @@ pub(crate) type ValTreeCreationResult<'tcx> = Result<ty::ValTree<'tcx>, ValTreeC
 
 #[instrument(skip(tcx), level = "debug")]
 pub(crate) fn try_destructure_mir_constant_for_user_output<'tcx>(
-    tcx: TyCtxtAt<'tcx>,
+    tcx: TyCtxt<'tcx>,
     val: mir::ConstValue<'tcx>,
     ty: Ty<'tcx>,
 ) -> Option<mir::DestructuredConstant<'tcx>> {
     let typing_env = ty::TypingEnv::fully_monomorphized();
-    let (ecx, op) = mk_eval_cx_for_const_val(tcx, typing_env, val, ty)?;
+    // FIXME: use a proper span here?
+    let (ecx, op) = mk_eval_cx_for_const_val(tcx.at(rustc_span::DUMMY_SP), typing_env, val, ty)?;
 
     // We go to `usize` as we cannot allocate anything bigger anyway.
     let (field_count, variant, down) = match ty.kind() {
-        ty::Array(_, len) => (len.try_to_target_usize(tcx.tcx)? as usize, None, op),
+        ty::Array(_, len) => (len.try_to_target_usize(tcx)? as usize, None, op),
         ty::Adt(def, _) if def.variants().is_empty() => {
             return None;
         }

compiler/rustc_const_eval/src/util/caller_location.rs

@@ -1,7 +1,6 @@
 use rustc_hir::LangItem;
-use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::layout::LayoutOf;
-use rustc_middle::ty::{self};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_middle::{bug, mir};
 use rustc_span::Symbol;
 use tracing::trace;
@@ -48,15 +47,15 @@ fn alloc_caller_location<'tcx>(
 }
 
 pub(crate) fn const_caller_location_provider(
-    tcx: TyCtxtAt<'_>,
+    tcx: TyCtxt<'_>,
     file: Symbol,
     line: u32,
     col: u32,
 ) -> mir::ConstValue<'_> {
     trace!("const_caller_location: {}:{}:{}", file, line, col);
     let mut ecx = mk_eval_cx_to_read_const_val(
-        tcx.tcx,
-        tcx.span,
+        tcx,
+        rustc_span::DUMMY_SP, // FIXME: use a proper span here?
         ty::TypingEnv::fully_monomorphized(),
         CanAccessMutGlobal::No,
     );