Rollup merge of #136279 - Zalathar:ensure-ok, r=oli-obk

Rename `tcx.ensure()` to `tcx.ensure_ok()`, and improve the associated docs

This is all based on my archaeology for https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/.60TyCtxtEnsure.60.

The main renamings are:
- `tcx.ensure()` → `tcx.ensure_ok()`
- `tcx.ensure_with_value()` → `tcx.ensure_done()`
- Query modifier `ensure_forwards_result_if_red` → `return_result_from_ensure_ok`

Hopefully these new names are a better fit for the *actual* function and purpose of these query call modes.

compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs

@@ -179,7 +179,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     return e;
                 }
 
-                if let Err(guar) = self.tcx.ensure().coherent_trait(trait_pred.def_id()) {
+                if let Err(guar) = self.tcx.ensure_ok().coherent_trait(trait_pred.def_id()) {
                     // Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
                     // other `Foo` impls are incoherent.
                     return guar;
@@ -511,8 +511,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     return e;
                 }
 
-                if let Err(guar) =
-                    self.tcx.ensure().coherent_trait(self.tcx.parent(data.projection_term.def_id))
+                if let Err(guar) = self
+                    .tcx
+                    .ensure_ok()
+                    .coherent_trait(self.tcx.parent(data.projection_term.def_id))
                 {
                     // Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
                     // other `Foo` impls are incoherent.

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -575,7 +575,7 @@ fn report_conflicting_impls<'tcx>(
     match used_to_be_allowed {
         None => {
             let reported = if overlap.with_impl.is_local()
-                || tcx.ensure().orphan_check_impl(impl_def_id).is_ok()
+                || tcx.ensure_ok().orphan_check_impl(impl_def_id).is_ok()
             {
                 let mut err = tcx.dcx().struct_span_err(impl_span, msg());
                 err.code(E0119);

compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs

@@ -379,7 +379,7 @@ pub(crate) fn assoc_def(
         // Ensure that the impl is constrained, otherwise projection may give us
         // bad unconstrained infer vars.
         if let Some(impl_def_id) = impl_def_id.as_local() {
-            tcx.ensure().enforce_impl_non_lifetime_params_are_constrained(impl_def_id)?;
+            tcx.ensure_ok().enforce_impl_non_lifetime_params_are_constrained(impl_def_id)?;
         }
 
         let item = tcx.associated_item(impl_item_id);
@@ -402,7 +402,7 @@ pub(crate) fn assoc_def(
         if assoc_item.item.container == ty::AssocItemContainer::Impl
             && let Some(impl_def_id) = assoc_item.item.container_id(tcx).as_local()
         {
-            tcx.ensure().enforce_impl_non_lifetime_params_are_constrained(impl_def_id)?;
+            tcx.ensure_ok().enforce_impl_non_lifetime_params_are_constrained(impl_def_id)?;
         }
 
         Ok(assoc_item)