Auto merge of rust-lang#16055 - Veykril:field-fallback-method, r=Veykril

Fallback to method resolution on unresolved field access with matching method name

Allows typing out a method name without having to add calling parentheses to do IDE things on it. The inverse of this we already have.

Author: bors

crates/hir-ty/src/infer/expr.rs

@@ -579,7 +579,7 @@ impl InferenceContext<'_> {
                 }
                 ty
             }
-            Expr::Field { expr, name } => self.infer_field_access(tgt_expr, *expr, name),
+            Expr::Field { expr, name } => self.infer_field_access(tgt_expr, *expr, name, expected),
             Expr::Await { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
@@ -1456,7 +1456,13 @@ impl InferenceContext<'_> {
         })
     }
 
-    fn infer_field_access(&mut self, tgt_expr: ExprId, receiver: ExprId, name: &Name) -> Ty {
+    fn infer_field_access(
+        &mut self,
+        tgt_expr: ExprId,
+        receiver: ExprId,
+        name: &Name,
+        expected: &Expectation,
+    ) -> Ty {
         let receiver_ty = self.infer_expr_inner(receiver, &Expectation::none());
 
         if name.is_missing() {
@@ -1482,28 +1488,42 @@ impl InferenceContext<'_> {
                 ty
             }
             None => {
-                // no field found,
-                let method_with_same_name_exists = {
-                    self.get_traits_in_scope();
-
-                    let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
-                    method_resolution::lookup_method(
-                        self.db,
-                        &canonicalized_receiver.value,
-                        self.table.trait_env.clone(),
-                        self.get_traits_in_scope().as_ref().left_or_else(|&it| it),
-                        VisibleFromModule::Filter(self.resolver.module()),
-                        name,
-                    )
-                    .is_some()
-                };
+                // no field found, lets attempt to resolve it like a function so that IDE things
+                // work out while people are typing
+                let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
+                let resolved = method_resolution::lookup_method(
+                    self.db,
+                    &canonicalized_receiver.value,
+                    self.table.trait_env.clone(),
+                    self.get_traits_in_scope().as_ref().left_or_else(|&it| it),
+                    VisibleFromModule::Filter(self.resolver.module()),
+                    name,
+                );
                 self.result.diagnostics.push(InferenceDiagnostic::UnresolvedField {
                     expr: tgt_expr,
-                    receiver: receiver_ty,
+                    receiver: receiver_ty.clone(),
                     name: name.clone(),
-                    method_with_same_name_exists,
+                    method_with_same_name_exists: resolved.is_some(),
                 });
-                self.err_ty()
+                match resolved {
+                    Some((adjust, func, _)) => {
+                        let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
+                        let generics = generics(self.db.upcast(), func.into());
+                        let substs = self.substs_for_method_call(generics, None);
+                        self.write_expr_adj(receiver, adjustments);
+                        self.write_method_resolution(tgt_expr, func, substs.clone());
+
+                        self.check_method_call(
+                            tgt_expr,
+                            &[],
+                            self.db.value_ty(func.into()),
+                            substs,
+                            ty,
+                            expected,
+                        )
+                    }
+                    None => self.err_ty(),
+                }
             }
         }
     }
@@ -1517,7 +1537,7 @@ impl InferenceContext<'_> {
         generic_args: Option<&GenericArgs>,
         expected: &Expectation,
     ) -> Ty {
-        let receiver_ty = self.infer_expr(receiver, &Expectation::none());
+        let receiver_ty = self.infer_expr_inner(receiver, &Expectation::none());
         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 
         let resolved = method_resolution::lookup_method(
@@ -1568,23 +1588,32 @@ impl InferenceContext<'_> {
                 )
             }
         };
+        self.check_method_call(tgt_expr, args, method_ty, substs, receiver_ty, expected)
+    }
+
+    fn check_method_call(
+        &mut self,
+        tgt_expr: ExprId,
+        args: &[ExprId],
+        method_ty: Binders<Ty>,
+        substs: Substitution,
+        receiver_ty: Ty,
+        expected: &Expectation,
+    ) -> Ty {
         let method_ty = method_ty.substitute(Interner, &substs);
         self.register_obligations_for_call(&method_ty);
-        let (formal_receiver_ty, param_tys, ret_ty, is_varargs) =
+        let ((formal_receiver_ty, param_tys), ret_ty, is_varargs) =
             match method_ty.callable_sig(self.db) {
-                Some(sig) => {
+                Some(sig) => (
                     if !sig.params().is_empty() {
-                        (
-                            sig.params()[0].clone(),
-                            sig.params()[1..].to_vec(),
-                            sig.ret().clone(),
-                            sig.is_varargs,
-                        )
+                        (sig.params()[0].clone(), sig.params()[1..].to_vec())
                     } else {
-                        (self.err_ty(), Vec::new(), sig.ret().clone(), sig.is_varargs)
-                    }
-                }
-                None => (self.err_ty(), Vec::new(), self.err_ty(), true),
+                        (self.err_ty(), Vec::new())
+                    },
+                    sig.ret().clone(),
+                    sig.is_varargs,
+                ),
+                None => ((self.err_ty(), Vec::new()), self.err_ty(), true),
             };
         self.unify(&formal_receiver_ty, &receiver_ty);
 

crates/hir/src/semantics.rs

@@ -17,7 +17,7 @@ use hir_def::{
     nameres::MacroSubNs,
     resolver::{self, HasResolver, Resolver, TypeNs},
     type_ref::Mutability,
-    AsMacroCall, DefWithBodyId, FieldId, FunctionId, MacroId, TraitId, VariantId,
+    AsMacroCall, DefWithBodyId, FunctionId, MacroId, TraitId, VariantId,
 };
 use hir_expand::{
     db::ExpandDatabase, files::InRealFile, name::AsName, ExpansionInfo, InMacroFile, MacroCallId,
@@ -198,20 +198,6 @@ impl<'db, DB: HirDatabase> Semantics<'db, DB> {
         self.imp.descend_node_at_offset(node, offset).filter_map(|mut it| it.find_map(N::cast))
     }
 
-    pub fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<Function> {
-        self.imp.resolve_method_call(call).map(Function::from)
-    }
-
-    /// Attempts to resolve this call expression as a method call falling back to resolving it as a field.
-    pub fn resolve_method_call_field_fallback(
-        &self,
-        call: &ast::MethodCallExpr,
-    ) -> Option<Either<Function, Field>> {
-        self.imp
-            .resolve_method_call_fallback(call)
-            .map(|it| it.map_left(Function::from).map_right(Field::from))
-    }
-
     pub fn resolve_await_to_poll(&self, await_expr: &ast::AwaitExpr) -> Option<Function> {
         self.imp.resolve_await_to_poll(await_expr).map(Function::from)
     }
@@ -1048,14 +1034,15 @@ impl<'db> SemanticsImpl<'db> {
         self.analyze(pat.syntax())?.binding_mode_of_pat(self.db, pat)
     }
 
-    fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<FunctionId> {
+    pub fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<Function> {
         self.analyze(call.syntax())?.resolve_method_call(self.db, call)
     }
 
-    fn resolve_method_call_fallback(
+    /// Attempts to resolve this call expression as a method call falling back to resolving it as a field.
+    pub fn resolve_method_call_fallback(
         &self,
         call: &ast::MethodCallExpr,
-    ) -> Option<Either<FunctionId, FieldId>> {
+    ) -> Option<Either<Function, Field>> {
         self.analyze(call.syntax())?.resolve_method_call_fallback(self.db, call)
     }
 
@@ -1087,6 +1074,13 @@ impl<'db> SemanticsImpl<'db> {
         self.analyze(field.syntax())?.resolve_field(self.db, field)
     }
 
+    pub fn resolve_field_fallback(
+        &self,
+        field: &ast::FieldExpr,
+    ) -> Option<Either<Field, Function>> {
+        self.analyze(field.syntax())?.resolve_field_fallback(self.db, field)
+    }
+
     pub fn resolve_record_field(
         &self,
         field: &ast::RecordExprField,
@@ -1298,7 +1292,7 @@ impl<'db> SemanticsImpl<'db> {
                     return None;
                 }
 
-                let func = self.resolve_method_call(method_call_expr).map(Function::from)?;
+                let func = self.resolve_method_call(method_call_expr)?;
                 let res = match func.self_param(self.db)?.access(self.db) {
                     Access::Shared | Access::Exclusive => true,
                     Access::Owned => false,

crates/hir/src/source_analyzer.rs

@@ -280,25 +280,49 @@ impl SourceAnalyzer {
         &self,
         db: &dyn HirDatabase,
         call: &ast::MethodCallExpr,
-    ) -> Option<FunctionId> {
+    ) -> Option<Function> {
         let expr_id = self.expr_id(db, &call.clone().into())?;
         let (f_in_trait, substs) = self.infer.as_ref()?.method_resolution(expr_id)?;
 
-        Some(self.resolve_impl_method_or_trait_def(db, f_in_trait, substs))
+        Some(self.resolve_impl_method_or_trait_def(db, f_in_trait, substs).into())
     }
 
     pub(crate) fn resolve_method_call_fallback(
         &self,
         db: &dyn HirDatabase,
         call: &ast::MethodCallExpr,
-    ) -> Option<Either<FunctionId, FieldId>> {
+    ) -> Option<Either<Function, Field>> {
         let expr_id = self.expr_id(db, &call.clone().into())?;
         let inference_result = self.infer.as_ref()?;
         match inference_result.method_resolution(expr_id) {
-            Some((f_in_trait, substs)) => {
-                Some(Either::Left(self.resolve_impl_method_or_trait_def(db, f_in_trait, substs)))
-            }
-            None => inference_result.field_resolution(expr_id).map(Either::Right),
+            Some((f_in_trait, substs)) => Some(Either::Left(
+                self.resolve_impl_method_or_trait_def(db, f_in_trait, substs).into(),
+            )),
+            None => inference_result.field_resolution(expr_id).map(Into::into).map(Either::Right),
+        }
+    }
+
+    pub(crate) fn resolve_field(
+        &self,
+        db: &dyn HirDatabase,
+        field: &ast::FieldExpr,
+    ) -> Option<Field> {
+        let expr_id = self.expr_id(db, &field.clone().into())?;
+        self.infer.as_ref()?.field_resolution(expr_id).map(|it| it.into())
+    }
+
+    pub(crate) fn resolve_field_fallback(
+        &self,
+        db: &dyn HirDatabase,
+        field: &ast::FieldExpr,
+    ) -> Option<Either<Field, Function>> {
+        let expr_id = self.expr_id(db, &field.clone().into())?;
+        let inference_result = self.infer.as_ref()?;
+        match inference_result.field_resolution(expr_id) {
+            Some(field) => Some(Either::Left(field.into())),
+            None => inference_result.method_resolution(expr_id).map(|(f, substs)| {
+                Either::Right(self.resolve_impl_method_or_trait_def(db, f, substs).into())
+            }),
         }
     }
 
@@ -417,15 +441,6 @@ impl SourceAnalyzer {
         Some(self.resolve_impl_method_or_trait_def(db, op_fn, substs))
     }
 
-    pub(crate) fn resolve_field(
-        &self,
-        db: &dyn HirDatabase,
-        field: &ast::FieldExpr,
-    ) -> Option<Field> {
-        let expr_id = self.expr_id(db, &field.clone().into())?;
-        self.infer.as_ref()?.field_resolution(expr_id).map(|it| it.into())
-    }
-
     pub(crate) fn resolve_record_field(
         &self,
         db: &dyn HirDatabase,

crates/ide-db/src/defs.rs

@@ -492,17 +492,20 @@ impl NameRefClass {
         match_ast! {
             match parent {
                 ast::MethodCallExpr(method_call) => {
-                    sema.resolve_method_call_field_fallback(&method_call)
+                    sema.resolve_method_call_fallback(&method_call)
                         .map(|it| {
                             it.map_left(Definition::Function)
                                 .map_right(Definition::Field)
                                 .either(NameRefClass::Definition, NameRefClass::Definition)
                         })
                 },
                 ast::FieldExpr(field_expr) => {
-                    sema.resolve_field(&field_expr)
-                        .map(Definition::Field)
-                        .map(NameRefClass::Definition)
+                    sema.resolve_field_fallback(&field_expr)
+                    .map(|it| {
+                        it.map_left(Definition::Field)
+                            .map_right(Definition::Function)
+                            .either(NameRefClass::Definition, NameRefClass::Definition)
+                    })
                 },
                 ast::RecordPatField(record_pat_field) => {
                     sema.resolve_record_pat_field(&record_pat_field)

crates/ide/src/hover/tests.rs

@@ -6698,3 +6698,30 @@ foo!(r"{$0aaaaa}");
         "#]],
     );
 }
+
+#[test]
+fn method_call_without_parens() {
+    check(
+        r#"
+struct S;
+impl S {
+    fn foo<T>(&self, t: T) {}
+}
+
+fn main() {
+    S.foo$0;
+}
+"#,
+        expect![[r#"
+            *foo*
+
+            ```rust
+            test::S
+            ```
+
+            ```rust
+            fn foo<T>(&self, t: T)
+            ```
+        "#]],
+    );
+}