Merge pull request #20721 from ChayimFriedman2/fix-never

fix: Implement fallback properly

Author: ChayimFriedman2

Cargo.lock

@@ -170,6 +170,7 @@ tracing-subscriber = { version = "0.3.20", default-features = false, features =
 triomphe = { version = "0.1.14", default-features = false, features = ["std"] }
 url = "2.5.4"
 xshell = "0.2.7"
+petgraph = { version = "0.8.2", default-features = false }
 
 # We need to freeze the version of the crate, as the raw-api feature is considered unstable
 dashmap = { version = "=6.1.0", features = ["raw-api", "inline"] }

Cargo.toml

@@ -34,6 +34,7 @@ rustc_apfloat = "0.2.3"
 query-group.workspace = true
 salsa.workspace = true
 salsa-macros.workspace = true
+petgraph.workspace = true
 
 ra-ap-rustc_abi.workspace = true
 ra-ap-rustc_index.workspace = true

crates/hir-ty/Cargo.toml

@@ -327,7 +327,7 @@ pub(crate) fn eval_to_const(
     debruijn: DebruijnIndex,
 ) -> Const {
     let db = ctx.db;
-    let infer = ctx.clone().resolve_all();
+    let infer = ctx.fixme_resolve_all_clone();
     fn has_closure(body: &Body, expr: ExprId) -> bool {
         if matches!(body[expr], Expr::Closure { .. }) {
             return true;

crates/hir-ty/src/consteval.rs

@@ -36,12 +36,12 @@ fn check_fail(
     error: impl FnOnce(ConstEvalError) -> bool,
 ) {
     let (db, file_id) = TestDB::with_single_file(ra_fixture);
-    match eval_goal(&db, file_id) {
+    salsa::attach(&db, || match eval_goal(&db, file_id) {
         Ok(_) => panic!("Expected fail, but it succeeded"),
         Err(e) => {
-            assert!(error(simplify(e.clone())), "Actual error was: {}", pretty_print_err(e, db))
+            assert!(error(simplify(e.clone())), "Actual error was: {}", pretty_print_err(e, &db))
         }
-    }
+    })
 }
 
 #[track_caller]
@@ -79,36 +79,38 @@ fn check_answer(
     check: impl FnOnce(&[u8], &MemoryMap<'_>),
 ) {
     let (db, file_ids) = TestDB::with_many_files(ra_fixture);
-    let file_id = *file_ids.last().unwrap();
-    let r = match eval_goal(&db, file_id) {
-        Ok(t) => t,
-        Err(e) => {
-            let err = pretty_print_err(e, db);
-            panic!("Error in evaluating goal: {err}");
-        }
-    };
-    match &r.data(Interner).value {
-        chalk_ir::ConstValue::Concrete(c) => match &c.interned {
-            ConstScalar::Bytes(b, mm) => {
-                check(b, mm);
+    salsa::attach(&db, || {
+        let file_id = *file_ids.last().unwrap();
+        let r = match eval_goal(&db, file_id) {
+            Ok(t) => t,
+            Err(e) => {
+                let err = pretty_print_err(e, &db);
+                panic!("Error in evaluating goal: {err}");
             }
-            x => panic!("Expected number but found {x:?}"),
-        },
-        _ => panic!("result of const eval wasn't a concrete const"),
-    }
+        };
+        match &r.data(Interner).value {
+            chalk_ir::ConstValue::Concrete(c) => match &c.interned {
+                ConstScalar::Bytes(b, mm) => {
+                    check(b, mm);
+                }
+                x => panic!("Expected number but found {x:?}"),
+            },
+            _ => panic!("result of const eval wasn't a concrete const"),
+        }
+    });
 }
 
-fn pretty_print_err(e: ConstEvalError, db: TestDB) -> String {
+fn pretty_print_err(e: ConstEvalError, db: &TestDB) -> String {
     let mut err = String::new();
     let span_formatter = |file, range| format!("{file:?} {range:?}");
     let display_target =
-        DisplayTarget::from_crate(&db, *db.all_crates().last().expect("no crate graph present"));
+        DisplayTarget::from_crate(db, *db.all_crates().last().expect("no crate graph present"));
     match e {
         ConstEvalError::MirLowerError(e) => {
-            e.pretty_print(&mut err, &db, span_formatter, display_target)
+            e.pretty_print(&mut err, db, span_formatter, display_target)
         }
         ConstEvalError::MirEvalError(e) => {
-            e.pretty_print(&mut err, &db, span_formatter, display_target)
+            e.pretty_print(&mut err, db, span_formatter, display_target)
         }
     }
     .unwrap();

crates/hir-ty/src/consteval/tests.rs

@@ -222,7 +222,7 @@ pub(crate) fn const_eval_discriminant_variant(
 // and make this function private. See the fixme comment on `InferenceContext::resolve_all`.
 pub(crate) fn eval_to_const<'db>(expr: ExprId, ctx: &mut InferenceContext<'db>) -> Const<'db> {
     let interner = DbInterner::new_with(ctx.db, None, None);
-    let infer = ctx.clone().resolve_all();
+    let infer = ctx.fixme_resolve_all_clone();
     fn has_closure(body: &Body, expr: ExprId) -> bool {
         if matches!(body[expr], Expr::Closure { .. }) {
             return true;

crates/hir-ty/src/consteval_nextsolver.rs

@@ -19,6 +19,7 @@ pub(crate) mod closure;
 mod coerce;
 pub(crate) mod diagnostics;
 mod expr;
+mod fallback;
 mod mutability;
 mod pat;
 mod path;
@@ -53,16 +54,16 @@ use indexmap::IndexSet;
 use intern::sym;
 use la_arena::{ArenaMap, Entry};
 use rustc_hash::{FxHashMap, FxHashSet};
+use rustc_type_ir::inherent::Ty as _;
 use stdx::{always, never};
 use triomphe::Arc;
 
-use crate::db::InternedClosureId;
 use crate::{
     AliasEq, AliasTy, Binders, ClosureId, Const, DomainGoal, GenericArg, ImplTraitId, ImplTraitIdx,
     IncorrectGenericsLenKind, Interner, Lifetime, OpaqueTyId, ParamLoweringMode,
     PathLoweringDiagnostic, ProjectionTy, Substitution, TargetFeatures, TraitEnvironment, Ty,
     TyBuilder, TyExt,
-    db::HirDatabase,
+    db::{HirDatabase, InternedClosureId},
     fold_tys,
     generics::Generics,
     infer::{
@@ -75,6 +76,7 @@ use crate::{
     mir::MirSpan,
     next_solver::{
         self, DbInterner,
+        infer::{DefineOpaqueTypes, traits::ObligationCause},
         mapping::{ChalkToNextSolver, NextSolverToChalk},
     },
     static_lifetime, to_assoc_type_id,
@@ -138,6 +140,20 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer
 
     ctx.infer_mut_body();
 
+    ctx.type_inference_fallback();
+
+    // Comment from rustc:
+    // Even though coercion casts provide type hints, we check casts after fallback for
+    // backwards compatibility. This makes fallback a stronger type hint than a cast coercion.
+    let cast_checks = std::mem::take(&mut ctx.deferred_cast_checks);
+    for mut cast in cast_checks.into_iter() {
+        if let Err(diag) = cast.check(&mut ctx) {
+            ctx.diagnostics.push(diag);
+        }
+    }
+
+    ctx.table.select_obligations_where_possible();
+
     ctx.infer_closures();
 
     Arc::new(ctx.resolve_all())
@@ -165,7 +181,6 @@ pub(crate) fn normalize(db: &dyn HirDatabase, trait_env: Arc<TraitEnvironment<'_
 
     let ty_with_vars = table.normalize_associated_types_in(ty);
     table.select_obligations_where_possible();
-    table.propagate_diverging_flag();
     table.resolve_completely(ty_with_vars)
 }
 
@@ -686,6 +701,25 @@ impl Index<BindingId> for InferenceResult {
     }
 }
 
+#[derive(Debug, Clone)]
+struct InternedStandardTypesNextSolver<'db> {
+    unit: crate::next_solver::Ty<'db>,
+    never: crate::next_solver::Ty<'db>,
+    i32: crate::next_solver::Ty<'db>,
+    f64: crate::next_solver::Ty<'db>,
+}
+
+impl<'db> InternedStandardTypesNextSolver<'db> {
+    fn new(interner: DbInterner<'db>) -> Self {
+        Self {
+            unit: crate::next_solver::Ty::new_unit(interner),
+            never: crate::next_solver::Ty::new(interner, crate::next_solver::TyKind::Never),
+            i32: crate::next_solver::Ty::new_int(interner, rustc_type_ir::IntTy::I32),
+            f64: crate::next_solver::Ty::new_float(interner, rustc_type_ir::FloatTy::F64),
+        }
+    }
+}
+
 /// The inference context contains all information needed during type inference.
 #[derive(Clone, Debug)]
 pub(crate) struct InferenceContext<'db> {
@@ -718,6 +752,7 @@ pub(crate) struct InferenceContext<'db> {
     resume_yield_tys: Option<(Ty, Ty)>,
     diverges: Diverges,
     breakables: Vec<BreakableContext<'db>>,
+    types: InternedStandardTypesNextSolver<'db>,
 
     /// Whether we are inside the pattern of a destructuring assignment.
     inside_assignment: bool,
@@ -798,11 +833,13 @@ impl<'db> InferenceContext<'db> {
         resolver: Resolver<'db>,
     ) -> Self {
         let trait_env = db.trait_environment_for_body(owner);
+        let table = unify::InferenceTable::new(db, trait_env);
         InferenceContext {
+            types: InternedStandardTypesNextSolver::new(table.interner),
             target_features: OnceCell::new(),
             generics: OnceCell::new(),
             result: InferenceResult::default(),
-            table: unify::InferenceTable::new(db, trait_env),
+            table,
             tuple_field_accesses_rev: Default::default(),
             return_ty: TyKind::Error.intern(Interner), // set in collect_* calls
             resume_yield_tys: None,
@@ -865,24 +902,33 @@ impl<'db> InferenceContext<'db> {
         self.result.has_errors = true;
     }
 
-    // FIXME: This function should be private in module. It is currently only used in the consteval, since we need
-    // `InferenceResult` in the middle of inference. See the fixme comment in `consteval::eval_to_const`. If you
-    // used this function for another workaround, mention it here. If you really need this function and believe that
-    // there is no problem in it being `pub(crate)`, remove this comment.
-    pub(crate) fn resolve_all(mut self) -> InferenceResult {
-        self.table.select_obligations_where_possible();
-        self.table.fallback_if_possible();
+    /// Clones `self` and calls `resolve_all()` on it.
+    // FIXME: Remove this.
+    pub(crate) fn fixme_resolve_all_clone(&self) -> InferenceResult {
+        let mut ctx = self.clone();
+
+        ctx.type_inference_fallback();
 
         // Comment from rustc:
         // Even though coercion casts provide type hints, we check casts after fallback for
         // backwards compatibility. This makes fallback a stronger type hint than a cast coercion.
-        let cast_checks = std::mem::take(&mut self.deferred_cast_checks);
+        let cast_checks = std::mem::take(&mut ctx.deferred_cast_checks);
         for mut cast in cast_checks.into_iter() {
-            if let Err(diag) = cast.check(&mut self) {
-                self.diagnostics.push(diag);
+            if let Err(diag) = cast.check(&mut ctx) {
+                ctx.diagnostics.push(diag);
             }
         }
 
+        ctx.table.select_obligations_where_possible();
+
+        ctx.resolve_all()
+    }
+
+    // FIXME: This function should be private in module. It is currently only used in the consteval, since we need
+    // `InferenceResult` in the middle of inference. See the fixme comment in `consteval::eval_to_const`. If you
+    // used this function for another workaround, mention it here. If you really need this function and believe that
+    // there is no problem in it being `pub(crate)`, remove this comment.
+    pub(crate) fn resolve_all(self) -> InferenceResult {
         let InferenceContext {
             mut table, mut result, tuple_field_accesses_rev, diagnostics, ..
         } = self;
@@ -914,11 +960,6 @@ impl<'db> InferenceContext<'db> {
             diagnostics: _,
         } = &mut result;
 
-        // FIXME resolve obligations as well (use Guidance if necessary)
-        table.select_obligations_where_possible();
-
-        // make sure diverging type variables are marked as such
-        table.propagate_diverging_flag();
         for ty in type_of_expr.values_mut() {
             *ty = table.resolve_completely(ty.clone());
             *has_errors = *has_errors || ty.contains_unknown();
@@ -1673,6 +1714,22 @@ impl<'db> InferenceContext<'db> {
         self.resolve_associated_type_with_params(inner_ty, assoc_ty, &[])
     }
 
+    fn demand_eqtype(
+        &mut self,
+        expected: crate::next_solver::Ty<'db>,
+        actual: crate::next_solver::Ty<'db>,
+    ) {
+        let result = self
+            .table
+            .infer_ctxt
+            .at(&ObligationCause::new(), self.table.trait_env.env)
+            .eq(DefineOpaqueTypes::Yes, expected, actual)
+            .map(|infer_ok| self.table.register_infer_ok(infer_ok));
+        if let Err(_err) = result {
+            // FIXME: Emit diagnostic.
+        }
+    }
+
     fn resolve_associated_type_with_params(
         &mut self,
         inner_ty: Ty,

crates/hir-ty/src/infer.rs

@@ -210,9 +210,8 @@ impl<'a, 'b, 'db> Coerce<'a, 'b, 'db> {
         // Coercing from `!` to any type is allowed:
         if a.is_never() {
             // If we're coercing into an inference var, mark it as possibly diverging.
-            // FIXME: rustc does this differently.
-            if let TyKind::Infer(rustc_type_ir::TyVar(b)) = b.kind() {
-                self.table.set_diverging(b.as_u32().into(), chalk_ir::TyVariableKind::General);
+            if b.is_infer() {
+                self.table.set_diverging(b);
             }
 
             if self.coerce_never {
@@ -1613,16 +1612,21 @@ fn coerce<'db>(
             chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner),
         } == Some(iv))
     };
-    let fallback = |iv, kind, default, binder| match kind {
-        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv)
-            .map_or(default, |i| crate::BoundVar::new(binder, i).to_ty(Interner).cast(Interner)),
-        chalk_ir::VariableKind::Lifetime => find_var(iv).map_or(default, |i| {
-            crate::BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)
-        }),
-        chalk_ir::VariableKind::Const(ty) => find_var(iv).map_or(default, |i| {
-            crate::BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)
-        }),
+    let fallback = |iv, kind, binder| match kind {
+        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv).map_or_else(
+            || chalk_ir::TyKind::Error.intern(Interner).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_ty(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Lifetime => find_var(iv).map_or_else(
+            || crate::LifetimeData::Error.intern(Interner).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Const(ty) => find_var(iv).map_or_else(
+            || crate::unknown_const(ty.clone()).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_const(Interner, ty.clone()).cast(Interner),
+        ),
     };
     // FIXME also map the types in the adjustments
+    // FIXME: We don't fallback correctly since this is done on `InferenceContext` and we only have `InferenceTable`.
     Ok((adjustments, table.resolve_with_fallback(ty.to_chalk(table.interner), &fallback)))
 }