Improve detection of generics on lang items

compiler/rustc_error_codes/src/error_codes/E0152.md

@@ -6,7 +6,7 @@ Erroneous code example:
 #![feature(lang_items)]
 
 #[lang = "owned_box"]
-struct Foo; // error: duplicate lang item found: `owned_box`
+struct Foo<T>(T); // error: duplicate lang item found: `owned_box`
 ```
 
 Lang items are already implemented in the standard library. Unless you are

compiler/rustc_passes/src/lang_items.rs

@@ -17,7 +17,7 @@ use rustc_errors::{pluralize, struct_span_err};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
-use rustc_hir::lang_items::{extract, ITEM_REFS};
+use rustc_hir::lang_items::{extract, GenericRequirement, ITEM_REFS};
 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
 use rustc_span::Span;
 
@@ -182,121 +182,69 @@ impl LanguageItemCollector<'tcx> {
     }
 
     // Like collect_item() above, but also checks whether the lang item is declared
-    // with the right number of generic arguments if it is a trait.
+    // with the right number of generic arguments.
     fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
         let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
         let lang_item = LangItem::from_u32(item_index as u32).unwrap();
         let name = lang_item.name();
 
-        self.collect_item(item_index, item_def_id);
-
         // Now check whether the lang_item has the expected number of generic
-        // arguments if it is a trait. Generally speaking, binary and indexing
-        // operations have one (for the RHS/index), unary operations have none,
-        // and the rest also have none except for the closure traits (one for
-        // the argument list), generators (one for the resume argument),
-        // ordering/equality relations (one for the RHS), and various conversion
-        // traits.
-
-        let expected_num = match lang_item {
-            // Binary operations
-            LangItem::Add
-            | LangItem::Sub
-            | LangItem::Mul
-            | LangItem::Div
-            | LangItem::Rem
-            | LangItem::BitXor
-            | LangItem::BitAnd
-            | LangItem::BitOr
-            | LangItem::Shl
-            | LangItem::Shr
-            | LangItem::AddAssign
-            | LangItem::SubAssign
-            | LangItem::MulAssign
-            | LangItem::DivAssign
-            | LangItem::RemAssign
-            | LangItem::BitXorAssign
-            | LangItem::BitAndAssign
-            | LangItem::BitOrAssign
-            | LangItem::ShlAssign
-            | LangItem::ShrAssign
-            | LangItem::Index
-            | LangItem::IndexMut
-
-            // Miscellaneous
-            | LangItem::Unsize
-            | LangItem::CoerceUnsized
-            | LangItem::DispatchFromDyn
-            | LangItem::Fn
-            | LangItem::FnMut
-            | LangItem::FnOnce
-            | LangItem::Generator
-            | LangItem::PartialEq
-            | LangItem::PartialOrd
-                => Some(1),
-
-            // Unary operations
-            LangItem::Neg
-            | LangItem::Not
-
-            // Miscellaneous
-            | LangItem::Deref
-            | LangItem::DerefMut
-            | LangItem::Sized
-            | LangItem::StructuralPeq
-            | LangItem::StructuralTeq
-            | LangItem::Copy
-            | LangItem::Clone
-            | LangItem::Sync
-            | LangItem::DiscriminantKind
-            | LangItem::PointeeTrait
-            | LangItem::Freeze
-            | LangItem::Drop
-            | LangItem::Receiver
-            | LangItem::Future
-            | LangItem::Unpin
-            | LangItem::Termination
-            | LangItem::Try
-                => Some(0),
+        // arguments. Generally speaking, binary and indexing operations have
+        // one (for the RHS/index), unary operations have none, the closure
+        // traits have one for the argument list, generators have one for the
+        // resume argument, and ordering/equality relations have one for the RHS
+        // Some other types like Box and various functions like drop_in_place
+        // have minimum requirements.
 
-            // Not a trait
-            _ => None,
-        };
+        if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) = self.tcx.hir().get(hir_id)
+        {
+            let (actual_num, generics_span) = match kind.generics() {
+                Some(generics) => (generics.params.len(), generics.span),
+                None => (0, *item_span),
+            };
 
-        if let Some(expected_num) = expected_num {
-            let (actual_num, generics_span) = match self.tcx.hir().get(hir_id) {
-                hir::Node::Item(hir::Item {
-                    kind: hir::ItemKind::Trait(_, _, generics, ..),
-                    ..
-                }) => (generics.params.len(), generics.span),
-                _ => bug!("op/index/deref lang item target is not a trait: {:?}", lang_item),
+            let required = match lang_item.required_generics() {
+                GenericRequirement::Exact(num) if num != actual_num => {
+                    Some((format!("{}", num), pluralize!(num)))
+                }
+                GenericRequirement::Minimum(num) if actual_num < num => {
+                    Some((format!("at least {}", num), pluralize!(num)))
+                }
+                // If the number matches, or there is no requirement, handle it normally
+                _ => None,
             };
 
-            if expected_num != actual_num {
+            if let Some((range_str, pluralized)) = required {
                 // We are issuing E0718 "incorrect target" here, because while the
                 // item kind of the target is correct, the target is still wrong
                 // because of the wrong number of generic arguments.
                 struct_span_err!(
                     self.tcx.sess,
                     span,
                     E0718,
-                    "`{}` language item must be applied to a trait with {} generic argument{}",
+                    "`{}` language item must be applied to a {} with {} generic argument{}",
                     name,
-                    expected_num,
-                    pluralize!(expected_num)
+                    kind.descr(),
+                    range_str,
+                    pluralized,
                 )
                 .span_label(
                     generics_span,
                     format!(
-                        "this trait has {} generic argument{}, not {}",
+                        "this {} has {} generic argument{}",
+                        kind.descr(),
                         actual_num,
                         pluralize!(actual_num),
-                        expected_num
                     ),
                 )
                 .emit();
+
+                // return early to not collect the lang item
+                return;
             }
         }
+
+        self.collect_item(item_index, item_def_id);
     }
 }
 

src/test/ui/error-codes/E0152.rs

@@ -2,7 +2,7 @@
 #![feature(lang_items)]
 
 #[lang = "owned_box"]
-struct Foo; //~ ERROR E0152
+struct Foo<T>(T); //~ ERROR E0152
 
 fn main() {
 }

src/test/ui/error-codes/E0152.stderr

@@ -1,8 +1,8 @@
 error[E0152]: found duplicate lang item `owned_box`
   --> $DIR/E0152.rs:5:1
    |
-LL | struct Foo;
-   | ^^^^^^^^^^^
+LL | struct Foo<T>(T);
+   | ^^^^^^^^^^^^^^^^^
    |
    = note: the lang item is first defined in crate `alloc` (which `std` depends on)
    = note: first definition in `alloc` loaded from SYSROOT/liballoc-*.rlib

src/test/ui/lang-items/lang-item-correct-generics.rs

@@ -0,0 +1,28 @@
+// build-pass
+
+#![feature(lang_items,no_core)]
+#![no_core]
+#![crate_type="lib"]
+
+#[lang = "sized"]
+trait MySized {}
+
+#[lang = "copy"]
+trait MyCopy {}
+
+#[lang = "drop"]
+trait MyDrop<T> {}
+
+struct S;
+
+impl<T> MyDrop<T> for S {}
+
+#[lang = "i32"]
+impl<'a> i32 {
+    fn foo() {}
+}
+
+fn bar() {
+    i32::foo();
+    S;
+}

src/test/ui/lang-items/lang-item-generic-requirements.rs

@@ -0,0 +1,44 @@
+// Checks whether declaring a lang item with the wrong number
+// of generic arguments crashes the compiler (issue #83893, #87573, and part of #9307).
+
+#![feature(lang_items, no_core)]
+#![no_core]
+#![crate_type = "lib"]
+
+#[lang = "sized"]
+trait MySized {}
+
+#[lang = "add"]
+trait MyAdd<'a, T> {}
+//~^^ ERROR: `add` language item must be applied to a trait with 1 generic argument [E0718]
+
+#[lang = "drop_in_place"]
+//~^ ERROR `drop_in_place` language item must be applied to a function with at least 1 generic
+fn my_ptr_drop() {}
+
+#[lang = "index"]
+trait MyIndex<'a, T> {}
+//~^^ ERROR: `index` language item must be applied to a trait with 1 generic argument [E0718]
+
+#[lang = "phantom_data"]
+//~^ ERROR `phantom_data` language item must be applied to a struct with 1 generic argument
+struct MyPhantomData<T, U>;
+//~^ ERROR parameter `T` is never used
+//~| ERROR parameter `U` is never used
+
+fn ice() {
+    // Use add
+    let r = 5;
+    let a = 6;
+    r + a;
+
+    // Use drop in place
+    my_ptr_drop();
+
+    // Use index
+    let arr = [0; 5];
+    let _ = arr[2];
+
+    // Use phantomdata
+    let _ = MyPhantomData::<(), i32>;
+}

src/test/ui/lang-items/lang-item-generic-requirements.stderr

@@ -0,0 +1,56 @@
+error[E0718]: `add` language item must be applied to a trait with 1 generic argument
+  --> $DIR/lang-item-generic-requirements.rs:11:1
+   |
+LL | #[lang = "add"]
+   | ^^^^^^^^^^^^^^^
+LL | trait MyAdd<'a, T> {}
+   |            ------- this trait has 2 generic arguments
+
+error[E0718]: `drop_in_place` language item must be applied to a function with at least 1 generic argument
+  --> $DIR/lang-item-generic-requirements.rs:15:1
+   |
+LL | #[lang = "drop_in_place"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | fn my_ptr_drop() {}
+   |               - this function has 0 generic arguments
+
+error[E0718]: `index` language item must be applied to a trait with 1 generic argument
+  --> $DIR/lang-item-generic-requirements.rs:19:1
+   |
+LL | #[lang = "index"]
+   | ^^^^^^^^^^^^^^^^^
+LL | trait MyIndex<'a, T> {}
+   |              ------- this trait has 2 generic arguments
+
+error[E0718]: `phantom_data` language item must be applied to a struct with 1 generic argument
+  --> $DIR/lang-item-generic-requirements.rs:23:1
+   |
+LL | #[lang = "phantom_data"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | struct MyPhantomData<T, U>;
+   |                     ------ this struct has 2 generic arguments
+
+error[E0392]: parameter `T` is never used
+  --> $DIR/lang-item-generic-requirements.rs:25:22
+   |
+LL | struct MyPhantomData<T, U>;
+   |                      ^ unused parameter
+   |
+   = help: consider removing `T` or referring to it in a field
+   = help: if you intended `T` to be a const parameter, use `const T: usize` instead
+
+error[E0392]: parameter `U` is never used
+  --> $DIR/lang-item-generic-requirements.rs:25:25
+   |
+LL | struct MyPhantomData<T, U>;
+   |                         ^ unused parameter
+   |
+   = help: consider removing `U` or referring to it in a field
+   = help: if you intended `U` to be a const parameter, use `const U: usize` instead
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0392, E0718.
+For more information about an error, try `rustc --explain E0392`.