feat: add trait_impl_reduntant_assoc_item diagnostic

crates/hir/src/diagnostics.rs

@@ -55,6 +55,7 @@ fn from(d: $diag) -> AnyDiagnostic {
     ReplaceFilterMapNextWithFindMap,
     TraitImplIncorrectSafety,
     TraitImplMissingAssocItems,
+    TraitImplReduntantAssocItems,
     TraitImplOrphan,
     TypedHole,
     TypeMismatch,
@@ -310,3 +311,10 @@ pub struct TraitImplMissingAssocItems {
     pub impl_: AstPtr<ast::Impl>,
     pub missing: Vec<(Name, AssocItem)>,
 }
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TraitImplReduntantAssocItems {
+    pub file_id: HirFileId,
+    pub impl_: AstPtr<ast::Impl>,
+    pub reduntant: Vec<(Name, AssocItem)>,
+}

crates/hir/src/lib.rs

@@ -693,6 +693,25 @@ pub fn diagnostics(self, db: &dyn HirDatabase, acc: &mut Vec<AnyDiagnostic>) {
                     },
                 ));
 
+                let reduntant: Vec<_> = impl_assoc_items_scratch.iter()
+                .filter(|(id, name)| {
+                    !required_items.clone().any(|(impl_name, impl_item)| {
+                        discriminant(impl_item) == discriminant(id) && impl_name == name
+                    })
+                })
+                .map(|(item, name)| (name.clone(), AssocItem::from(*item)))
+                .collect();
+                if !reduntant.is_empty() {
+                    acc.push(
+                        TraitImplReduntantAssocItems {
+                            impl_: ast_id_map.get(node.ast_id()),
+                            file_id,
+                            reduntant,
+                        }
+                        .into(),
+                    )
+                }
+
                 let missing: Vec<_> = required_items
                     .filter(|(name, id)| {
                         !impl_assoc_items_scratch.iter().any(|(impl_item, impl_name)| {

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

@@ -0,0 +1,56 @@
+use hir::InFile;
+use itertools::Itertools;
+use syntax::{ast, AstNode};
+
+use crate::{adjusted_display_range, Diagnostic, DiagnosticCode, DiagnosticsContext};
+
+// Diagnostic: trait-impl-reduntant-assoc_item
+//
+// Diagnoses reduntant trait items in a trait impl.
+pub(crate) fn trait_impl_reduntant_assoc_item(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::TraitImplReduntantAssocItems,
+) -> Diagnostic {
+    let reduntant = d.reduntant.iter().format_with(", ", |(name, item), f| {
+        f(&match *item {
+            hir::AssocItem::Function(_) => "`fn ",
+            hir::AssocItem::Const(_) => "`const ",
+            hir::AssocItem::TypeAlias(_) => "`type ",
+        })?;
+        f(&name.display(ctx.sema.db))?;
+        f(&"`")
+    });
+    Diagnostic::new(
+        DiagnosticCode::RustcHardError("E0407"),
+        format!("{reduntant} is not a member of trait"),
+        adjusted_display_range::<ast::Impl>(
+            ctx,
+            InFile { file_id: d.file_id, value: d.impl_.syntax_node_ptr() },
+            &|impl_| impl_.trait_().map(|t| t.syntax().text_range()),
+        ),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn trait_with_default_value() {
+        check_diagnostics(
+            r#"
+trait Marker {
+    fn boo();
+}
+struct Foo;
+impl Marker for Foo {
+   //^^^^^^ error: `type T`, `const FLAG`, `fn bar` is not a member of trait
+    type T = i32;
+    const FLAG: bool = false;
+    fn bar() {}
+    fn boo() {}
+}
+            "#,
+        )
+    }
+}

crates/ide-diagnostics/src/lib.rs

@@ -47,6 +47,7 @@ mod handlers {
     pub(crate) mod trait_impl_orphan;
     pub(crate) mod trait_impl_incorrect_safety;
     pub(crate) mod trait_impl_missing_assoc_item;
+    pub(crate) mod trait_impl_reduntant_assoc_item;
     pub(crate) mod typed_hole;
     pub(crate) mod type_mismatch;
     pub(crate) mod unimplemented_builtin_macro;
@@ -364,6 +365,7 @@ pub fn diagnostics(
             AnyDiagnostic::ReplaceFilterMapNextWithFindMap(d) => handlers::replace_filter_map_next_with_find_map::replace_filter_map_next_with_find_map(&ctx, &d),
             AnyDiagnostic::TraitImplIncorrectSafety(d) => handlers::trait_impl_incorrect_safety::trait_impl_incorrect_safety(&ctx, &d),
             AnyDiagnostic::TraitImplMissingAssocItems(d) => handlers::trait_impl_missing_assoc_item::trait_impl_missing_assoc_item(&ctx, &d),
+            AnyDiagnostic::TraitImplReduntantAssocItems(d) => handlers::trait_impl_reduntant_assoc_item::trait_impl_reduntant_assoc_item(&ctx, &d),
             AnyDiagnostic::TraitImplOrphan(d) => handlers::trait_impl_orphan::trait_impl_orphan(&ctx, &d),
             AnyDiagnostic::TypedHole(d) => handlers::typed_hole::typed_hole(&ctx, &d),
             AnyDiagnostic::TypeMismatch(d) => handlers::type_mismatch::type_mismatch(&ctx, &d),