Diagnose private field accesses

crates/hir-ty/src/infer.rs

@@ -208,6 +208,7 @@ pub(crate) type InferResult<T> = Result<InferOk<T>, TypeError>;
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum InferenceDiagnostic {
     NoSuchField { expr: ExprId },
+    PrivateField { expr: ExprId, field: FieldId },
     BreakOutsideOfLoop { expr: ExprId, is_break: bool },
     MismatchedArgCount { call_expr: ExprId, expected: usize, found: usize },
 }

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

@@ -1,7 +1,6 @@
 //! Type inference for expressions.
 
 use std::{
-    collections::hash_map::Entry,
     iter::{repeat, repeat_with},
     mem,
 };
@@ -521,6 +520,7 @@ impl<'a> InferenceContext<'a> {
                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 
                 let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
+                let mut private_field = None;
                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
                     let (field_id, parameters) = match derefed_ty.kind(Interner) {
                         TyKind::Tuple(_, substs) => {
@@ -547,13 +547,8 @@ impl<'a> InferenceContext<'a> {
                     let is_visible = self.db.field_visibilities(field_id.parent)[field_id.local_id]
                         .is_visible_from(self.db.upcast(), self.resolver.module());
                     if !is_visible {
-                        // Write down the first field resolution even if it is not visible
-                        // This aids IDE features for private fields like goto def and in
-                        // case of autoderef finding an applicable field, this will be
-                        // overwritten in a following cycle
-                        if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
-                        {
-                            entry.insert(field_id);
+                        if private_field.is_none() {
+                            private_field = Some(field_id);
                         }
                         return None;
                     }
@@ -572,7 +567,17 @@ impl<'a> InferenceContext<'a> {
                         let ty = self.normalize_associated_types_in(ty);
                         ty
                     }
-                    _ => self.err_ty(),
+                    _ => {
+                        // Write down the first private field resolution if we found no field
+                        // This aids IDE features for private fields like goto def
+                        if let Some(field) = private_field {
+                            self.result.field_resolutions.insert(tgt_expr, field);
+                            self.result
+                                .diagnostics
+                                .push(InferenceDiagnostic::PrivateField { expr: tgt_expr, field });
+                        }
+                        self.err_ty()
+                    }
                 };
                 ty
             }

crates/hir/src/diagnostics.rs

@@ -10,7 +10,7 @@ use hir_def::path::ModPath;
 use hir_expand::{name::Name, HirFileId, InFile};
 use syntax::{ast, AstPtr, SyntaxNodePtr, TextRange};
 
-use crate::{MacroKind, Type};
+use crate::{Field, MacroKind, Type};
 
 macro_rules! diagnostics {
     ($($diag:ident,)*) => {
@@ -41,6 +41,7 @@ diagnostics![
     MissingMatchArms,
     MissingUnsafe,
     NoSuchField,
+    PrivateField,
     ReplaceFilterMapNextWithFindMap,
     TypeMismatch,
     UnimplementedBuiltinMacro,
@@ -121,6 +122,12 @@ pub struct NoSuchField {
     pub field: InFile<AstPtr<ast::RecordExprField>>,
 }
 
+#[derive(Debug)]
+pub struct PrivateField {
+    pub expr: InFile<AstPtr<ast::Expr>>,
+    pub field: Field,
+}
+
 #[derive(Debug)]
 pub struct BreakOutsideOfLoop {
     pub expr: InFile<AstPtr<ast::Expr>>,

crates/hir/src/lib.rs

@@ -85,7 +85,7 @@ pub use crate::{
     diagnostics::{
         AnyDiagnostic, BreakOutsideOfLoop, InactiveCode, IncorrectCase, InvalidDeriveTarget,
         MacroError, MalformedDerive, MismatchedArgCount, MissingFields, MissingMatchArms,
-        MissingUnsafe, NoSuchField, ReplaceFilterMapNextWithFindMap, TypeMismatch,
+        MissingUnsafe, NoSuchField, PrivateField, ReplaceFilterMapNextWithFindMap, TypeMismatch,
         UnimplementedBuiltinMacro, UnresolvedExternCrate, UnresolvedImport, UnresolvedMacroCall,
         UnresolvedModule, UnresolvedProcMacro,
     },
@@ -1353,6 +1353,11 @@ impl DefWithBody {
                         Err(SyntheticSyntax) => (),
                     }
                 }
+                &hir_ty::InferenceDiagnostic::PrivateField { expr, field } => {
+                    let expr = source_map.expr_syntax(expr).expect("unexpected synthetic");
+                    let field = field.into();
+                    acc.push(PrivateField { expr, field }.into())
+                }
             }
         }
         for (expr, mismatch) in infer.expr_type_mismatches() {

crates/ide-diagnostics/src/handlers/private_field.rs

@@ -0,0 +1,55 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: private-field
+//
+// This diagnostic is triggered if created structure does not have field provided in record.
+pub(crate) fn private_field(ctx: &DiagnosticsContext<'_>, d: &hir::PrivateField) -> Diagnostic {
+    // FIXME: add quickfix
+    Diagnostic::new(
+        "private-field",
+        format!(
+            "field `{}` of `{}` is private",
+            d.field.name(ctx.sema.db),
+            d.field.parent_def(ctx.sema.db).name(ctx.sema.db)
+        ),
+        ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn private_field() {
+        check_diagnostics(
+            r#"
+mod module { pub struct Struct { field: u32 } }
+fn main(s: module::Struct) {
+    s.field;
+  //^^^^^^^ error: field `field` of `Struct` is private
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn private_but_shadowed_in_deref() {
+        check_diagnostics(
+            r#"
+//- minicore: deref
+mod module {
+    pub struct Struct { field: Inner }
+    pub struct Inner { pub field: u32 }
+    impl core::ops::Deref for Struct {
+        type Target = Inner;
+        fn deref(&self) -> &Inner { &self.field }
+    }
+}
+fn main(s: module::Struct) {
+    s.field;
+}
+"#,
+        );
+    }
+}

crates/ide-diagnostics/src/lib.rs

@@ -37,6 +37,7 @@ mod handlers {
     pub(crate) mod missing_match_arms;
     pub(crate) mod missing_unsafe;
     pub(crate) mod no_such_field;
+    pub(crate) mod private_field;
     pub(crate) mod replace_filter_map_next_with_find_map;
     pub(crate) mod type_mismatch;
     pub(crate) mod unimplemented_builtin_macro;
@@ -254,6 +255,7 @@ pub fn diagnostics(
             AnyDiagnostic::MissingMatchArms(d) => handlers::missing_match_arms::missing_match_arms(&ctx, &d),
             AnyDiagnostic::MissingUnsafe(d) => handlers::missing_unsafe::missing_unsafe(&ctx, &d),
             AnyDiagnostic::NoSuchField(d) => handlers::no_such_field::no_such_field(&ctx, &d),
+            AnyDiagnostic::PrivateField(d) => handlers::private_field::private_field(&ctx, &d),
             AnyDiagnostic::ReplaceFilterMapNextWithFindMap(d) => handlers::replace_filter_map_next_with_find_map::replace_filter_map_next_with_find_map(&ctx, &d),
             AnyDiagnostic::TypeMismatch(d) => handlers::type_mismatch::type_mismatch(&ctx, &d),
             AnyDiagnostic::UnimplementedBuiltinMacro(d) => handlers::unimplemented_builtin_macro::unimplemented_builtin_macro(&ctx, &d),