Auto merge of #119146 - nnethercote:rm-DiagCtxt-api-duplication, r=compiler-errors

Remove `DiagCtxt` API duplication

`DiagCtxt` defines the internal API for creating and emitting diagnostics: methods like `struct_err`, `struct_span_warn`, `note`, `create_fatal`, `emit_bug`. There are over 50 methods.

Some of these methods are then duplicated across several other types: `Session`, `ParseSess`, `Parser`, `ExtCtxt`, and `MirBorrowckCtxt`. `Session` duplicates the most, though half the ones it does are unused. Each duplicated method just calls forward to the corresponding method in `DiagCtxt`. So this duplication exists to (in the best case) shorten chains like `ecx.tcx.sess.parse_sess.dcx.emit_err()` to `ecx.emit_err()`.

This API duplication is ugly and has been bugging me for a while. And it's inconsistent: there's no real logic about which methods are duplicated, and the use of `#[rustc_lint_diagnostic]` and `#[track_caller]` attributes vary across the duplicates.

This PR removes the duplicated API methods and makes all diagnostic creation and emission go through `DiagCtxt`. It also adds `dcx` getter methods to several types to shorten chains. This approach scales *much* better than API duplication; indeed, the PR adds `dcx()` to numerous types that didn't have API duplication: `TyCtxt`, `LoweringCtxt`, `ConstCx`, `FnCtxt`, `TypeErrCtxt`, `InferCtxt`, `CrateLoader`, `CheckAttrVisitor`, and `Resolver`. These result in a lot of changes from `foo.tcx.sess.emit_err()` to `foo.dcx().emit_err()`. (You could do this with more types, but it gets into diminishing returns territory for types that don't emit many diagnostics.)

After all these changes, some call sites are more verbose, some are less verbose, and many are the same. The total number of lines is reduced, mostly because of the removed API duplication. And consistency is increased, because calls to `emit_err` and friends are always preceded with `.dcx()` or `.dcx`.

r? `@compiler-errors`

5 files changed, 7 insertions, 7 deletions

diff --git a/compiler/rustc_mir_transform/src/check_packed_ref.rs b/compiler/rustc_mir_transform/src/check_packed_ref.rs
index 77bcba50a3c..a405ed6088d 100644
--- a/compiler/rustc_mir_transform/src/check_packed_ref.rs
+++ b/compiler/rustc_mir_transform/src/check_packed_ref.rs
@@ -52,7 +52,7 @@ impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
                     );
                 } else {
                     self.tcx
-                        .sess
+                        .dcx()
                         .emit_err(errors::UnalignedPackedRef { span: self.source_info.span });
                 }
             }
diff --git a/compiler/rustc_mir_transform/src/check_unsafety.rs b/compiler/rustc_mir_transform/src/check_unsafety.rs
index f246de55ca8..23726e49f4d 100644
--- a/compiler/rustc_mir_transform/src/check_unsafety.rs
+++ b/compiler/rustc_mir_transform/src/check_unsafety.rs
@@ -242,7 +242,7 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
                     if assigned_ty.needs_drop(self.tcx, self.param_env) {
                         // This would be unsafe, but should be outright impossible since we reject such unions.
-                        self.tcx.sess.span_delayed_bug(
+                        self.tcx.dcx().span_delayed_bug(
                             self.source_info.span,
                             format!("union fields that need dropping should be impossible: {assigned_ty}")
                         );
@@ -568,7 +568,7 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
                 } else {
                     None
                 };
-                tcx.sess.emit_err(errors::RequiresUnsafe {
+                tcx.dcx().emit_err(errors::RequiresUnsafe {
                     span: source_info.span,
                     enclosing,
                     details,
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 6da102dcb1c..d1d5b72af70 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -1604,7 +1604,7 @@ impl<'tcx> MirPass<'tcx> for StateTransform {
                 (args.discr_ty(tcx), movability == hir::Movability::Movable)
             }
             _ => {
-                tcx.sess.span_delayed_bug(
+                tcx.dcx().span_delayed_bug(
                     body.span,
                     format!("unexpected coroutine type {coroutine_ty}"),
                 );
diff --git a/compiler/rustc_mir_transform/src/elaborate_drops.rs b/compiler/rustc_mir_transform/src/elaborate_drops.rs
index c45badbc559..8575f552f0a 100644
--- a/compiler/rustc_mir_transform/src/elaborate_drops.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_drops.rs
@@ -315,7 +315,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
                     self.init_data.seek_before(self.body.terminator_loc(bb));
                     let (_maybe_live, maybe_dead) = self.init_data.maybe_live_dead(parent);
                     if maybe_dead {
-                        self.tcx.sess.span_delayed_bug(
+                        self.tcx.dcx().span_delayed_bug(
                             terminator.source_info.span,
                             format!(
                                 "drop of untracked, uninitialized value {bb:?}, place {place:?} ({path:?})"
@@ -380,7 +380,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
                 LookupResult::Parent(None) => {}
                 LookupResult::Parent(Some(_)) => {
                     if !replace {
-                        self.tcx.sess.span_delayed_bug(
+                        self.tcx.dcx().span_delayed_bug(
                             terminator.source_info.span,
                             format!("drop of untracked value {bb:?}"),
                         );
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 98d4d96d0c7..9d03bab4844 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -267,7 +267,7 @@ fn mir_const_qualif(tcx: TyCtxt<'_>, def: LocalDefId) -> ConstQualifs {
     let body = &tcx.mir_const(def).borrow();
 
     if body.return_ty().references_error() {
-        tcx.sess.span_delayed_bug(body.span, "mir_const_qualif: MIR had errors");
+        tcx.dcx().span_delayed_bug(body.span, "mir_const_qualif: MIR had errors");
         return Default::default();
     }