Split -Zchalk flag into -Ztrait-solver=(stock|chalk|next) flag

compiler/rustc_interface/src/tests.rs

@@ -4,6 +4,7 @@ use crate::interface::parse_cfgspecs;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{emitter::HumanReadableErrorType, registry, ColorConfig};
 use rustc_session::config::rustc_optgroups;
+use rustc_session::config::TraitSolver;
 use rustc_session::config::{build_configuration, build_session_options, to_crate_config};
 use rustc_session::config::{
     BranchProtection, Externs, OomStrategy, OutputType, OutputTypes, PAuthKey, PacRet,
@@ -722,7 +723,6 @@ fn test_unstable_options_tracking_hash() {
             pac_ret: Some(PacRet { leaf: true, key: PAuthKey::B })
         })
     );
-    tracked!(chalk, true);
     tracked!(codegen_backend, Some("abc".to_string()));
     tracked!(crate_attr, vec!["abc".to_string()]);
     tracked!(debug_info_for_profiling, true);
@@ -792,6 +792,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(thinlto, Some(true));
     tracked!(thir_unsafeck, true);
     tracked!(tls_model, Some(TlsModel::GeneralDynamic));
+    tracked!(trait_solver, TraitSolver::Chalk);
     tracked!(translate_remapped_path_to_local_path, false);
     tracked!(trap_unreachable, Some(false));
     tracked!(treat_err_as_bug, NonZeroUsize::new(1));

compiler/rustc_session/src/config.rs

@@ -554,6 +554,16 @@ pub enum PrintRequest {
     SplitDebuginfo,
 }
 
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+pub enum TraitSolver {
+    /// Stock trait solver in `rustc_trait_selection::traits::select`
+    Stock,
+    /// Chalk trait solver
+    Chalk,
+    /// Experimental trait solver in `rustc_trait_selection::solve`
+    Next,
+}
+
 pub enum Input {
     /// Load source code from a file.
     File(PathBuf),
@@ -2761,7 +2771,7 @@ pub(crate) mod dep_tracking {
         BranchProtection, CFGuard, CFProtection, CrateType, DebugInfo, ErrorOutputType,
         InstrumentCoverage, LdImpl, LinkerPluginLto, LocationDetail, LtoCli, OomStrategy, OptLevel,
         OutputType, OutputTypes, Passes, SourceFileHashAlgorithm, SplitDwarfKind,
-        SwitchWithOptPath, SymbolManglingVersion, TrimmedDefPaths,
+        SwitchWithOptPath, SymbolManglingVersion, TraitSolver, TrimmedDefPaths,
     };
     use crate::lint;
     use crate::options::WasiExecModel;
@@ -2861,6 +2871,7 @@ pub(crate) mod dep_tracking {
         BranchProtection,
         OomStrategy,
         LanguageIdentifier,
+        TraitSolver,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)

compiler/rustc_session/src/options.rs

@@ -382,6 +382,8 @@ mod desc {
         "`all` (default), `except-unused-generics`, `except-unused-functions`, or `off`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
     pub const parse_treat_err_as_bug: &str = "either no value or a number bigger than 0";
+    pub const parse_trait_solver: &str =
+        "one of the supported solver modes (`stock`, `chalk`, or `next`)";
     pub const parse_lto: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted";
     pub const parse_linker_plugin_lto: &str =
@@ -880,6 +882,16 @@ mod parse {
         }
     }
 
+    pub(crate) fn parse_trait_solver(slot: &mut TraitSolver, v: Option<&str>) -> bool {
+        match v {
+            Some("stock") => *slot = TraitSolver::Stock,
+            Some("chalk") => *slot = TraitSolver::Chalk,
+            Some("next") => *slot = TraitSolver::Next,
+            _ => return false,
+        }
+        true
+    }
+
     pub(crate) fn parse_lto(slot: &mut LtoCli, v: Option<&str>) -> bool {
         if v.is_some() {
             let mut bool_arg = None;
@@ -1249,8 +1261,6 @@ options! {
         "instrument control-flow architecture protection"),
     cgu_partitioning_strategy: Option<String> = (None, parse_opt_string, [TRACKED],
         "the codegen unit partitioning strategy to use"),
-    chalk: bool = (false, parse_bool, [TRACKED],
-        "enable the experimental Chalk-based trait solving engine"),
     codegen_backend: Option<String> = (None, parse_opt_string, [TRACKED],
         "the backend to use"),
     combine_cgu: bool = (false, parse_bool, [TRACKED],
@@ -1609,6 +1619,8 @@ options! {
         "for every macro invocation, print its name and arguments (default: no)"),
     track_diagnostics: bool = (false, parse_bool, [UNTRACKED],
         "tracks where in rustc a diagnostic was emitted"),
+    trait_solver: TraitSolver = (TraitSolver::Stock, parse_trait_solver, [TRACKED],
+        "specify the trait solver mode used by rustc (default: stock)"),
     // Diagnostics are considered side-effects of a query (see `QuerySideEffects`) and are saved
     // alongside query results and changes to translation options can affect diagnostics - so
     // translation options should be tracked.

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -3,6 +3,7 @@ use std::fmt::Debug;
 
 use super::TraitEngine;
 use super::{ChalkFulfillmentContext, FulfillmentContext};
+use crate::solve::FulfillmentCtxt as NextFulfillmentCtxt;
 use crate::traits::NormalizeExt;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -20,6 +21,7 @@ use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_session::config::TraitSolver;
 use rustc_span::Span;
 
 pub trait TraitEngineExt<'tcx> {
@@ -29,18 +31,18 @@ pub trait TraitEngineExt<'tcx> {
 
 impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
     fn new(tcx: TyCtxt<'tcx>) -> Box<Self> {
-        if tcx.sess.opts.unstable_opts.chalk {
-            Box::new(ChalkFulfillmentContext::new())
-        } else {
-            Box::new(FulfillmentContext::new())
+        match tcx.sess.opts.unstable_opts.trait_solver {
+            TraitSolver::Stock => Box::new(FulfillmentContext::new()),
+            TraitSolver::Chalk => Box::new(ChalkFulfillmentContext::new()),
+            TraitSolver::Next => Box::new(NextFulfillmentCtxt::new()),
         }
     }
 
     fn new_in_snapshot(tcx: TyCtxt<'tcx>) -> Box<Self> {
-        if tcx.sess.opts.unstable_opts.chalk {
-            Box::new(ChalkFulfillmentContext::new_in_snapshot())
-        } else {
-            Box::new(FulfillmentContext::new_in_snapshot())
+        match tcx.sess.opts.unstable_opts.trait_solver {
+            TraitSolver::Stock => Box::new(FulfillmentContext::new_in_snapshot()),
+            TraitSolver::Chalk => Box::new(ChalkFulfillmentContext::new_in_snapshot()),
+            TraitSolver::Next => Box::new(NextFulfillmentCtxt::new()),
         }
     }
 }

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

@@ -40,6 +40,7 @@ use rustc_middle::ty::{
     self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
     TypeVisitable,
 };
+use rustc_session::config::TraitSolver;
 use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::symbol::sym;
@@ -1167,7 +1168,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     }
 
                     ty::PredicateKind::WellFormed(ty) => {
-                        if !self.tcx.sess.opts.unstable_opts.chalk {
+                        if self.tcx.sess.opts.unstable_opts.trait_solver != TraitSolver::Chalk {
                             // WF predicates cannot themselves make
                             // errors. They can only block due to
                             // ambiguity; otherwise, they always

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -15,6 +15,7 @@ use rustc_middle::ty::{
     self, Binder, GenericArg, GenericArgKind, GenericParamDefKind, InternalSubsts, SubstsRef,
     ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt,
 };
+use rustc_session::config::TraitSolver;
 use rustc_span::def_id::DefId;
 
 use crate::traits::project::{normalize_with_depth, normalize_with_depth_to};
@@ -767,8 +768,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!(?closure_def_id, ?trait_ref, ?nested, "confirm closure candidate obligations");
 
         // FIXME: Chalk
-
-        if !self.tcx().sess.opts.unstable_opts.chalk {
+        if self.tcx().sess.opts.unstable_opts.trait_solver != TraitSolver::Chalk {
             nested.push(obligation.with(
                 self.tcx(),
                 ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, substs, kind)),

compiler/rustc_ty_utils/src/ty.rs

@@ -2,6 +2,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
+use rustc_session::config::TraitSolver;
 use rustc_trait_selection::traits;
 
 fn sized_constraint_for_ty<'tcx>(
@@ -121,7 +122,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     // are any errors at that point, so outside of type inference you can be
     // sure that this will succeed without errors anyway.
 
-    if tcx.sess.opts.unstable_opts.chalk {
+    if tcx.sess.opts.unstable_opts.trait_solver == TraitSolver::Chalk {
         let environment = well_formed_types_in_env(tcx, def_id);
         predicates.extend(environment);
     }