Auto merge of #118937 - lcnr:rename-solver-flag, r=compiler-errors

`-Ztrait-solver=next` to `-Znext-solver`

renames the feature flag to enable the new trait solver.

still want some feedback before merging: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/renaming.20the.20feature.20flag.20to.20.60-Znew-solver.60.

The idea is to make it easier to add another option, e.g. to enable the solver in wfcheck or to optionally change its behavior to our new coinduction approach.

r? `@compiler-errors`

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -315,7 +315,7 @@ fn check_opaque_type_well_formed<'tcx>(
         parent_def_id = tcx.local_parent(parent_def_id);
     }
 
-    // FIXME(-Ztrait-solver=next): We probably should use `DefiningAnchor::Error`
+    // FIXME(-Znext-solver): We probably should use `DefiningAnchor::Error`
     // and prepopulate this `InferCtxt` with known opaque values, rather than
     // using the `Bind` anchor here. For now it's fine.
     let infcx = tcx

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1003,16 +1003,16 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             reported_errors: Default::default(),
         };
 
-        // FIXME(-Ztrait-solver=next): A bit dubious that we're only registering
+        // FIXME(-Znext-solver): A bit dubious that we're only registering
         // predefined opaques in the typeck root.
         if infcx.next_trait_solver() && !infcx.tcx.is_typeck_child(body.source.def_id()) {
-            checker.register_predefined_opaques_in_new_solver();
+            checker.register_predefined_opaques_for_next_solver();
         }
 
         checker
     }
 
-    pub(super) fn register_predefined_opaques_in_new_solver(&mut self) {
+    pub(super) fn register_predefined_opaques_for_next_solver(&mut self) {
         // OK to use the identity arguments for each opaque type key, since
         // we remap opaques from HIR typeck back to their definition params.
         let opaques: Vec<_> = self

compiler/rustc_codegen_cranelift/example/gen_block_iterate.rs

@@ -1,7 +1,7 @@
 // Copied from https://github.com/rust-lang/rust/blob/46455dc65069387f2dc46612f13fd45452ab301a/tests/ui/coroutine/gen_block_iterate.rs
 // revisions: next old
 //compile-flags: --edition 2024 -Zunstable-options
-//[next] compile-flags: -Ztrait-solver=next
+//[next] compile-flags: -Znext-solver
 // run-pass
 #![feature(gen_blocks)]
 

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -320,7 +320,7 @@ fn compare_method_predicate_entailment<'tcx>(
     if check_implied_wf == CheckImpliedWfMode::Check && !(impl_sig, trait_sig).references_error() {
         // Select obligations to make progress on inference before processing
         // the wf obligation below.
-        // FIXME(-Ztrait-solver=next): Not needed when the hack below is removed.
+        // FIXME(-Znext-solver): Not needed when the hack below is removed.
         let errors = ocx.select_where_possible();
         if !errors.is_empty() {
             let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
@@ -333,7 +333,7 @@ fn compare_method_predicate_entailment<'tcx>(
         // trigger the lint. Instead, let's only consider type outlives and
         // region outlives obligations.
         //
-        // FIXME(-Ztrait-solver=next): Try removing this hack again once
+        // FIXME(-Znext-solver): Try removing this hack again once
         // the new solver is stable.
         let mut wf_args: smallvec::SmallVec<[_; 4]> =
             unnormalized_impl_sig.inputs_and_output.iter().map(|ty| ty.into()).collect();

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1019,7 +1019,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Returns false if the coercion creates any obligations that result in
     /// errors.
     pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
-        // FIXME(-Ztrait-solver=next): We need to structurally resolve both types here.
+        // FIXME(-Znext-solver): We need to structurally resolve both types here.
         let source = self.resolve_vars_with_obligations(expr_ty);
         debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
 

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -83,7 +83,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// version (resolve_vars_if_possible), this version will
     /// also select obligations if it seems useful, in an effort
     /// to get more type information.
-    // FIXME(-Ztrait-solver=next): A lot of the calls to this method should
+    // FIXME(-Znext-solver): A lot of the calls to this method should
     // probably be `try_structurally_resolve_type` or `structurally_resolve_type` instead.
     #[instrument(skip(self), level = "debug", ret)]
     pub(in super::super) fn resolve_vars_with_obligations(&self, mut ty: Ty<'tcx>) -> Ty<'tcx> {

compiler/rustc_infer/src/infer/canonical/mod.rs

@@ -101,7 +101,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// variable, then you'll get a new inference variable; if it is a
     /// universally quantified variable, you get a placeholder.
     ///
-    /// FIXME(-Ztrait-solver=next): This is public because it's used by the
+    /// FIXME(-Znext-solver): This is public because it's used by the
     /// new trait solver which has a different canonicalization routine.
     /// We should somehow deduplicate all of this.
     pub fn instantiate_canonical_var(

compiler/rustc_infer/src/infer/canonical/substitute.rs

@@ -11,7 +11,7 @@ use rustc_middle::ty::fold::{FnMutDelegate, TypeFoldable};
 use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{self, TyCtxt};
 
-/// FIXME(-Ztrait-solver=next): This or public because it is shared with the
+/// FIXME(-Znext-solver): This or public because it is shared with the
 /// new trait solver implementation. We should deduplicate canonicalization.
 pub trait CanonicalExt<'tcx, V> {
     /// Instantiate the wrapped value, replacing each canonical value

compiler/rustc_infer/src/traits/mod.rs

@@ -135,7 +135,7 @@ pub enum FulfillmentErrorCode<'tcx> {
     CodeSubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate
     CodeConstEquateError(ExpectedFound<Const<'tcx>>, TypeError<'tcx>),
     CodeAmbiguity {
-        /// Overflow reported from the new solver `-Ztrait-solver=next`, which will
+        /// Overflow reported from the new solver `-Znext-solver`, which will
         /// be reported as an regular error as opposed to a fatal error.
         overflow: bool,
     },

compiler/rustc_interface/src/tests.rs

@@ -6,10 +6,9 @@ use rustc_session::config::{
     build_configuration, build_session_options, rustc_optgroups, BranchProtection, CFGuard, Cfg,
     DebugInfo, DumpMonoStatsFormat, ErrorOutputType, ExternEntry, ExternLocation, Externs,
     FunctionReturn, InliningThreshold, Input, InstrumentCoverage, InstrumentXRay,
-    LinkSelfContained, LinkerPluginLto, LocationDetail, LtoCli, MirSpanview, OomStrategy, Options,
-    OutFileName, OutputType, OutputTypes, PAuthKey, PacRet, Passes, Polonius,
-    ProcMacroExecutionStrategy, Strip, SwitchWithOptPath, SymbolManglingVersion, TraitSolver,
-    WasiExecModel,
+    LinkSelfContained, LinkerPluginLto, LocationDetail, LtoCli, MirSpanview, NextSolverConfig,
+    OomStrategy, Options, OutFileName, OutputType, OutputTypes, PAuthKey, PacRet, Passes, Polonius,
+    ProcMacroExecutionStrategy, Strip, SwitchWithOptPath, SymbolManglingVersion, WasiExecModel,
 };
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
@@ -781,6 +780,10 @@ fn test_unstable_options_tracking_hash() {
     tracked!(mir_opt_level, Some(4));
     tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, false);
+    tracked!(
+        next_solver,
+        Some(NextSolverConfig { coherence: true, globally: false, dump_tree: Default::default() })
+    );
     tracked!(no_generate_arange_section, true);
     tracked!(no_jump_tables, true);
     tracked!(no_link, true);
@@ -822,7 +825,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(thir_unsafeck, true);
     tracked!(tiny_const_eval_limit, true);
     tracked!(tls_model, Some(TlsModel::GeneralDynamic));
-    tracked!(trait_solver, TraitSolver::NextCoherence);
     tracked!(translate_remapped_path_to_local_path, false);
     tracked!(trap_unreachable, Some(false));
     tracked!(treat_err_as_bug, NonZeroUsize::new(1));

compiler/rustc_middle/src/traits/solve/cache.rs

@@ -5,7 +5,7 @@ use rustc_data_structures::sync::Lock;
 use rustc_query_system::cache::WithDepNode;
 use rustc_query_system::dep_graph::DepNodeIndex;
 use rustc_session::Limit;
-/// The trait solver cache used by `-Ztrait-solver=next`.
+/// The trait solver cache used by `-Znext-solver`.
 ///
 /// FIXME(@lcnr): link to some official documentation of how
 /// this works.

compiler/rustc_middle/src/ty/context.rs

@@ -2240,15 +2240,11 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn next_trait_solver_globally(self) -> bool {
-        self.sess.opts.unstable_opts.trait_solver == rustc_session::config::TraitSolver::Next
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally)
     }
 
     pub fn next_trait_solver_in_coherence(self) -> bool {
-        matches!(
-            self.sess.opts.unstable_opts.trait_solver,
-            rustc_session::config::TraitSolver::Next
-                | rustc_session::config::TraitSolver::NextCoherence
-        )
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.coherence)
     }
 
     pub fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -62,7 +62,7 @@ pub enum TreatParams {
     ///
     /// N.B. during deep rejection, this acts identically to `ForLookup`.
     ///
-    /// FIXME(-Ztrait-solver=next): Remove this variant and cleanup
+    /// FIXME(-Znext-solver): Remove this variant and cleanup
     /// the code.
     NextSolverLookup,
 }

compiler/rustc_session/src/config.rs

@@ -755,13 +755,14 @@ pub enum PrintKind {
 }
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
-pub enum TraitSolver {
-    /// Classic trait solver in `rustc_trait_selection::traits::select`
-    Classic,
-    /// Experimental trait solver in `rustc_trait_selection::solve`
-    Next,
-    /// Use the new trait solver during coherence
-    NextCoherence,
+pub struct NextSolverConfig {
+    /// Whether the new trait solver should be enabled in coherence.
+    pub coherence: bool,
+    /// Whether the new trait solver should be enabled everywhere.
+    /// This is only `true` if `coherence` is also enabled.
+    pub globally: bool,
+    /// Whether to dump proof trees after computing a proof tree.
+    pub dump_tree: DumpSolverProofTree,
 }
 
 #[derive(Default, Debug, Copy, Clone, Hash, PartialEq, Eq)]
@@ -3220,10 +3221,10 @@ pub(crate) mod dep_tracking {
     use super::{
         BranchProtection, CFGuard, CFProtection, CrateType, DebugInfo, DebugInfoCompression,
         ErrorOutputType, FunctionReturn, InliningThreshold, InstrumentCoverage, InstrumentXRay,
-        LinkerPluginLto, LocationDetail, LtoCli, OomStrategy, OptLevel, OutFileName, OutputType,
-        OutputTypes, Polonius, RemapPathScopeComponents, ResolveDocLinks, SourceFileHashAlgorithm,
-        SplitDwarfKind, SwitchWithOptPath, SymbolManglingVersion, TraitSolver, TrimmedDefPaths,
-        WasiExecModel,
+        LinkerPluginLto, LocationDetail, LtoCli, NextSolverConfig, OomStrategy, OptLevel,
+        OutFileName, OutputType, OutputTypes, Polonius, RemapPathScopeComponents, ResolveDocLinks,
+        SourceFileHashAlgorithm, SplitDwarfKind, SwitchWithOptPath, SymbolManglingVersion,
+        TrimmedDefPaths, WasiExecModel,
     };
     use crate::lint;
     use crate::utils::NativeLib;
@@ -3326,7 +3327,7 @@ pub(crate) mod dep_tracking {
         BranchProtection,
         OomStrategy,
         LanguageIdentifier,
-        TraitSolver,
+        NextSolverConfig,
         Polonius,
         InliningThreshold,
         FunctionReturn,

compiler/rustc_session/src/options.rs

@@ -396,8 +396,7 @@ mod desc {
     pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
     pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
-    pub const parse_trait_solver: &str =
-        "one of the supported solver modes (`classic`, `next`, or `next-coherence`)";
+    pub const parse_next_solver_config: &str = "a comma separated list of solver configurations: `globally` (default), `coherence`, `dump-tree`, `dump-tree-on-error";
     pub const parse_lto: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted";
     pub const parse_linker_plugin_lto: &str =
@@ -429,7 +428,6 @@ mod desc {
         "a `,` separated combination of `bti`, `b-key`, `pac-ret`, or `leaf`";
     pub const parse_proc_macro_execution_strategy: &str =
         "one of supported execution strategies (`same-thread`, or `cross-thread`)";
-    pub const parse_dump_solver_proof_tree: &str = "one of: `always`, `on-request`, `on-error`";
     pub const parse_remap_path_scope: &str = "comma separated list of scopes: `macro`, `diagnostics`, `unsplit-debuginfo`, `split-debuginfo`, `split-debuginfo-path`, `object`, `all`";
     pub const parse_inlining_threshold: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), or a non-negative number";
@@ -1032,15 +1030,48 @@ mod parse {
         }
     }
 
-    pub(crate) fn parse_trait_solver(slot: &mut TraitSolver, v: Option<&str>) -> bool {
-        match v {
-            Some("classic") => *slot = TraitSolver::Classic,
-            Some("next") => *slot = TraitSolver::Next,
-            Some("next-coherence") => *slot = TraitSolver::NextCoherence,
-            // default trait solver is subject to change..
-            Some("default") => *slot = TraitSolver::Classic,
-            _ => return false,
+    pub(crate) fn parse_next_solver_config(
+        slot: &mut Option<NextSolverConfig>,
+        v: Option<&str>,
+    ) -> bool {
+        if let Some(config) = v {
+            let mut coherence = false;
+            let mut globally = true;
+            let mut dump_tree = None;
+            for c in config.split(',') {
+                match c {
+                    "globally" => globally = true,
+                    "coherence" => {
+                        globally = false;
+                        coherence = true;
+                    }
+                    "dump-tree" => {
+                        if dump_tree.replace(DumpSolverProofTree::Always).is_some() {
+                            return false;
+                        }
+                    }
+                    "dump-tree-on-error" => {
+                        if dump_tree.replace(DumpSolverProofTree::OnError).is_some() {
+                            return false;
+                        }
+                    }
+                    _ => return false,
+                }
+            }
+
+            *slot = Some(NextSolverConfig {
+                coherence: coherence || globally,
+                globally,
+                dump_tree: dump_tree.unwrap_or_default(),
+            });
+        } else {
+            *slot = Some(NextSolverConfig {
+                coherence: true,
+                globally: true,
+                dump_tree: Default::default(),
+            });
         }
+
         true
     }
 
@@ -1305,19 +1336,6 @@ mod parse {
         true
     }
 
-    pub(crate) fn parse_dump_solver_proof_tree(
-        slot: &mut DumpSolverProofTree,
-        v: Option<&str>,
-    ) -> bool {
-        match v {
-            None | Some("always") => *slot = DumpSolverProofTree::Always,
-            Some("never") => *slot = DumpSolverProofTree::Never,
-            Some("on-error") => *slot = DumpSolverProofTree::OnError,
-            _ => return false,
-        };
-        true
-    }
-
     pub(crate) fn parse_inlining_threshold(slot: &mut InliningThreshold, v: Option<&str>) -> bool {
         match v {
             Some("always" | "yes") => {
@@ -1591,9 +1609,6 @@ options! {
         "output statistics about monomorphization collection"),
     dump_mono_stats_format: DumpMonoStatsFormat = (DumpMonoStatsFormat::Markdown, parse_dump_mono_stats, [UNTRACKED],
         "the format to use for -Z dump-mono-stats (`markdown` (default) or `json`)"),
-    dump_solver_proof_tree: DumpSolverProofTree = (DumpSolverProofTree::Never, parse_dump_solver_proof_tree, [UNTRACKED],
-        "dump a proof tree for every goal evaluated by the new trait solver. If the flag is specified without any options after it
-        then it defaults to `always`. If the flag is not specified at all it defaults to `on-request`."),
     dwarf_version: Option<u32> = (None, parse_opt_number, [TRACKED],
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     dylib_lto: bool = (false, parse_bool, [UNTRACKED],
@@ -1722,6 +1737,8 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
+    next_solver: Option<NextSolverConfig> = (None, parse_next_solver_config, [TRACKED],
+        "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
         "dump facts from NLL analysis into side files (default: no)"),
     nll_facts_dir: String = ("nll-facts".to_string(), parse_string, [UNTRACKED],
@@ -1922,8 +1939,6 @@ written to standard error output)"),
         "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::Classic, parse_trait_solver, [TRACKED],
-        "specify the trait solver mode used by rustc (default: classic)"),
     // 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/solve/eval_ctxt/mod.rs

@@ -200,9 +200,10 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         let result = f(&mut ecx);
 
         let tree = ecx.inspect.finalize();
-        if let (Some(tree), DumpSolverProofTree::Always) =
-            (&tree, infcx.tcx.sess.opts.unstable_opts.dump_solver_proof_tree)
-        {
+        if let (Some(tree), DumpSolverProofTree::Always) = (
+            &tree,
+            infcx.tcx.sess.opts.unstable_opts.next_solver.map(|c| c.dump_tree).unwrap_or_default(),
+        ) {
             let mut lock = std::io::stdout().lock();
             let _ = lock.write_fmt(format_args!("{tree:?}\n"));
             let _ = lock.flush();
@@ -377,7 +378,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         //
         // This assert was removed as it did not hold for goals constraining
         // an inference variable to a recursive alias, e.g. in
-        // tests/ui/traits/new-solver/overflow/recursive-self-normalization.rs.
+        // tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs.
         //
         // Once we have decided on how to handle trait-system-refactor-initiative#75,
         // we should re-add an assert here.
@@ -421,7 +422,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                     self.compute_const_evaluatable_goal(Goal { param_env, predicate: ct })
                 }
                 ty::PredicateKind::ConstEquate(_, _) => {
-                    bug!("ConstEquate should not be emitted when `-Ztrait-solver=next` is active")
+                    bug!("ConstEquate should not be emitted when `-Znext-solver` is active")
                 }
                 ty::PredicateKind::NormalizesTo(predicate) => {
                     self.compute_normalizes_to_goal(Goal { param_env, predicate })

compiler/rustc_trait_selection/src/solve/inspect/build.rs

@@ -265,7 +265,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
             GenerateProofTree::Never => ProofTreeBuilder::new_noop(),
             GenerateProofTree::IfEnabled => {
                 let opts = &tcx.sess.opts.unstable_opts;
-                match opts.dump_solver_proof_tree {
+                match opts.next_solver.map(|c| c.dump_tree).unwrap_or_default() {
                     DumpSolverProofTree::Always => ProofTreeBuilder::new_root(),
                     // `OnError` is handled by reevaluating goals in error
                     // reporting with `GenerateProofTree::Yes`.