Rollup merge of #132119 - compiler-errors:effects-old-solver, r=lcnr

Hack out effects support for old solver

Opening this for vibes ✨

Turns out that a basic, somewhat incomplete implementation of host effects is achievable in the old trait solver pretty easily. This should be sufficient for us to use in the standard library itself.

Regarding incompleteness, maybe we should always treat host predicates as ambiguous in intercrate mode (at least in the old solver) to avoid any worries about accidental impl overlap or something.

r? ```@lcnr``` cc ```@fee1-dead```

compiler/rustc_hir_analysis/messages.ftl

@@ -149,10 +149,6 @@ hir_analysis_drop_impl_reservation = reservation `Drop` impls are not supported
 hir_analysis_duplicate_precise_capture = cannot capture parameter `{$name}` twice
     .label = parameter captured again here
 
-hir_analysis_effects_without_next_solver = using `#![feature(effects)]` without enabling next trait solver globally
-    .note = the next trait solver must be enabled globally for the effects feature to work correctly
-    .help = use `-Znext-solver` to enable
-
 hir_analysis_empty_specialization = specialization impl does not specialize any associated items
     .note = impl is a specialization of this impl
 

compiler/rustc_hir_analysis/src/errors.rs

@@ -1623,12 +1623,6 @@ pub(crate) struct InvalidReceiverTy<'tcx> {
     pub receiver_ty: Ty<'tcx>,
 }
 
-#[derive(Diagnostic)]
-#[diag(hir_analysis_effects_without_next_solver)]
-#[note]
-#[help]
-pub(crate) struct EffectsWithoutNextSolver;
-
 #[derive(Diagnostic)]
 #[diag(hir_analysis_cmse_inputs_stack_spill, code = E0798)]
 #[note]

compiler/rustc_hir_analysis/src/lib.rs

@@ -153,12 +153,6 @@ pub fn provide(providers: &mut Providers) {
 pub fn check_crate(tcx: TyCtxt<'_>) {
     let _prof_timer = tcx.sess.timer("type_check_crate");
 
-    // FIXME(effects): remove once effects is implemented in old trait solver
-    // or if the next solver is stabilized.
-    if tcx.features().effects() && !tcx.next_trait_solver_globally() {
-        tcx.dcx().emit_err(errors::EffectsWithoutNextSolver);
-    }
-
     tcx.sess.time("coherence_checking", || {
         tcx.hir().par_for_each_module(|module| {
             let _ = tcx.ensure().check_mod_type_wf(module);