Rollup merge of #129467 - dingxiangfei2009:smart-pointer-relax-pointee, r=compiler-errors

derive(SmartPointer): assume pointee from the single generic and better error messages Fix #129465 Actually RFC says that `#[pointee]` can be inferred when there is no ambiguity, or there is only one generic type parameter so to say. cc ```@Darksonn``` r? ```@compiler-errors```
2024-08-28 19:12:52 -07:00 · 2024-08-28 19:12:52 -07:00 · d2418cb888
commit d2418cb888
parent 9d5f794312 39148351bd
5 changed files with 108 additions and 44 deletions
--- a/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
@ -11,7 +11,6 @@
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{Span, Symbol};
-use smallvec::{smallvec, SmallVec};
 use thin_vec::{thin_vec, ThinVec};

 macro_rules! path {
@ -68,43 +67,63 @@ pub(crate) fn expand_deriving_smart_ptr(
    };

    // Convert generic parameters (from the struct) into generic args.
-    let mut pointee_param = None;
-    let mut multiple_pointee_diag: SmallVec<[_; 2]> = smallvec![];
-    let self_params = generics
+    let self_params: Vec<_> = generics
+        .params
+        .iter()
+        .map(|p| match p.kind {
+            GenericParamKind::Lifetime => GenericArg::Lifetime(cx.lifetime(p.span(), p.ident)),
+            GenericParamKind::Type { .. } => GenericArg::Type(cx.ty_ident(p.span(), p.ident)),
+            GenericParamKind::Const { .. } => GenericArg::Const(cx.const_ident(p.span(), p.ident)),
+        })
+        .collect();
+    let type_params: Vec<_> = generics
        .params
        .iter()
        .enumerate()
-        .map(|(idx, p)| match p.kind {
-            GenericParamKind::Lifetime => GenericArg::Lifetime(cx.lifetime(p.span(), p.ident)),
-            GenericParamKind::Type { .. } => {
-                if p.attrs().iter().any(|attr| attr.has_name(sym::pointee)) {
-                    if pointee_param.is_some() {
-                        multiple_pointee_diag.push(cx.dcx().struct_span_err(
-                            p.span(),
-                            "`SmartPointer` can only admit one type as pointee",
-                        ));
-                    } else {
-                        pointee_param = Some(idx);
-                    }
-                }
-                GenericArg::Type(cx.ty_ident(p.span(), p.ident))
+        .filter_map(|(idx, p)| {
+            if let GenericParamKind::Type { .. } = p.kind {
+                Some((idx, p.span(), p.attrs().iter().any(|attr| attr.has_name(sym::pointee))))
+            } else {
+                None
            }
-            GenericParamKind::Const { .. } => GenericArg::Const(cx.const_ident(p.span(), p.ident)),
        })
-        .collect::<Vec<_>>();
-    let Some(pointee_param_idx) = pointee_param else {
+        .collect();
+
+    let pointee_param_idx = if type_params.is_empty() {
+        // `#[derive(SmartPointer)]` requires at least one generic type on the target `struct`
        cx.dcx().struct_span_err(
            span,
-            "At least one generic type should be designated as `#[pointee]` in order to derive `SmartPointer` traits",
+            "`SmartPointer` can only be derived on `struct`s that are generic over at least one type",
        ).emit();
        return;
-    };
-    if !multiple_pointee_diag.is_empty() {
-        for diag in multiple_pointee_diag {
-            diag.emit();
+    } else if type_params.len() == 1 {
+        // Regardless of the only type param being designed as `#[pointee]` or not, we can just use it as such
+        type_params[0].0
+    } else {
+        let mut pointees = type_params
+            .iter()
+            .filter_map(|&(idx, span, is_pointee)| is_pointee.then_some((idx, span)))
+            .fuse();
+        match (pointees.next(), pointees.next()) {
+            (Some((idx, _span)), None) => idx,
+            (None, _) => {
+                cx.dcx().struct_span_err(
+                    span,
+                    "exactly one generic type parameter must be marked as #[pointee] to derive SmartPointer traits",
+                ).emit();
+                return;
+            }
+            (Some((_, one)), Some((_, another))) => {
+                cx.dcx()
+                    .struct_span_err(
+                        vec![one, another],
+                        "only one type parameter can be marked as `#[pointee]` when deriving SmartPointer traits",
+                    )
+                    .emit();
+                return;
+            }
        }
-        return;
-    }
+    };

    // Create the type of `self`.
    let path = cx.path_all(span, false, vec![name_ident], self_params.clone());
--- a/tests/ui/deriving/deriving-smart-pointer-expanded.rs
+++ b/tests/ui/deriving/deriving-smart-pointer-expanded.rs
@ -20,3 +20,9 @@ pub struct MyPointer2<'a, Y, Z: MyTrait<T>, #[pointee] T: ?Sized + MyTrait<T>, X
    data: &'a mut T,
    x: core::marker::PhantomData<X>,
 }
+
+#[derive(SmartPointer)]
+#[repr(transparent)]
+struct MyPointerWithoutPointee<'a, T: ?Sized> {
+    ptr: &'a T,
+}
--- a/tests/ui/deriving/deriving-smart-pointer-expanded.stdout
+++ b/tests/ui/deriving/deriving-smart-pointer-expanded.stdout
@ -42,3 +42,18 @@ impl<'a, Y, Z: MyTrait<T> + MyTrait<__S>, T: ?Sized + MyTrait<T> +
    MyTrait<__S>> ::core::ops::CoerceUnsized<MyPointer2<'a, Y, Z, __S, X>> for
    MyPointer2<'a, Y, Z, T, X> where Y: MyTrait<T>, Y: MyTrait<__S> {
 }
+
+#[repr(transparent)]
+struct MyPointerWithoutPointee<'a, T: ?Sized> {
+    ptr: &'a T,
+}
+#[automatically_derived]
+impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
+    ::core::ops::DispatchFromDyn<MyPointerWithoutPointee<'a, __S>> for
+    MyPointerWithoutPointee<'a, T> {
+}
+#[automatically_derived]
+impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
+    ::core::ops::CoerceUnsized<MyPointerWithoutPointee<'a, __S>> for
+    MyPointerWithoutPointee<'a, T> {
+}
--- a/tests/ui/deriving/deriving-smart-pointer-neg.rs
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.rs
@ -9,13 +9,6 @@ enum NotStruct<'a, T: ?Sized> {
    Variant(&'a T),
 }

-#[derive(SmartPointer)]
-//~^ ERROR: At least one generic type should be designated as `#[pointee]` in order to derive `SmartPointer` traits
-#[repr(transparent)]
-struct NoPointee<'a, T: ?Sized> {
-    ptr: &'a T,
-}
-
 #[derive(SmartPointer)]
 //~^ ERROR: `SmartPointer` can only be derived on `struct`s with at least one field
 #[repr(transparent)]
@ -30,6 +23,23 @@ struct NoField<'a, #[pointee] T: ?Sized> {}
 //~^ ERROR: lifetime parameter `'a` is never used
 //~| ERROR: type parameter `T` is never used

+#[derive(SmartPointer)]
+//~^ ERROR: `SmartPointer` can only be derived on `struct`s that are generic over at least one type
+#[repr(transparent)]
+struct NoGeneric<'a>(&'a u8);
+
+#[derive(SmartPointer)]
+//~^ ERROR: exactly one generic type parameter must be marked as #[pointee] to derive SmartPointer traits
+#[repr(transparent)]
+struct AmbiguousPointee<'a, T1: ?Sized, T2: ?Sized> {
+    a: (&'a T1, &'a T2),
+}
+
+#[derive(SmartPointer)]
+#[repr(transparent)]
+struct TooManyPointees<'a, #[pointee] A: ?Sized, #[pointee] B: ?Sized>((&'a A, &'a B));
+//~^ ERROR: only one type parameter can be marked as `#[pointee]` when deriving SmartPointer traits
+
 #[derive(SmartPointer)]
 //~^ ERROR: `SmartPointer` can only be derived on `struct`s with `#[repr(transparent)]`
 struct NotTransparent<'a, #[pointee] T: ?Sized> {
--- a/tests/ui/deriving/deriving-smart-pointer-neg.stderr
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.stderr
@ -6,7 +6,7 @@ LL | #[derive(SmartPointer)]
   |
   = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)

-error: At least one generic type should be designated as `#[pointee]` in order to derive `SmartPointer` traits
+error: `SmartPointer` can only be derived on `struct`s with at least one field
  --> $DIR/deriving-smart-pointer-neg.rs:12:10
   |
 LL | #[derive(SmartPointer)]
@ -22,7 +22,7 @@ LL | #[derive(SmartPointer)]
   |
   = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)

-error: `SmartPointer` can only be derived on `struct`s with at least one field
+error: `SmartPointer` can only be derived on `struct`s that are generic over at least one type
  --> $DIR/deriving-smart-pointer-neg.rs:26:10
   |
 LL | #[derive(SmartPointer)]
@ -30,8 +30,22 @@ LL | #[derive(SmartPointer)]
   |
   = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)

+error: exactly one generic type parameter must be marked as #[pointee] to derive SmartPointer traits
+  --> $DIR/deriving-smart-pointer-neg.rs:31:10
+   |
+LL | #[derive(SmartPointer)]
+   |          ^^^^^^^^^^^^
+   |
+   = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: only one type parameter can be marked as `#[pointee]` when deriving SmartPointer traits
+  --> $DIR/deriving-smart-pointer-neg.rs:40:39
+   |
+LL | struct TooManyPointees<'a, #[pointee] A: ?Sized, #[pointee] B: ?Sized>((&'a A, &'a B));
+   |                                       ^                     ^
+
 error: `SmartPointer` can only be derived on `struct`s with `#[repr(transparent)]`
-  --> $DIR/deriving-smart-pointer-neg.rs:33:10
+  --> $DIR/deriving-smart-pointer-neg.rs:43:10
   |
 LL | #[derive(SmartPointer)]
   |          ^^^^^^^^^^^^
@ -39,13 +53,13 @@ LL | #[derive(SmartPointer)]
   = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)

 error: `derive(SmartPointer)` requires T to be marked `?Sized`
-  --> $DIR/deriving-smart-pointer-neg.rs:41:36
+  --> $DIR/deriving-smart-pointer-neg.rs:51:36
   |
 LL | struct NoMaybeSized<'a, #[pointee] T> {
   |                                    ^

 error[E0392]: lifetime parameter `'a` is never used
-  --> $DIR/deriving-smart-pointer-neg.rs:22:16
+  --> $DIR/deriving-smart-pointer-neg.rs:15:16
   |
 LL | struct NoField<'a, #[pointee] T: ?Sized> {}
   |                ^^ unused lifetime parameter
@ -53,7 +67,7 @@ LL | struct NoField<'a, #[pointee] T: ?Sized> {}
   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`

 error[E0392]: type parameter `T` is never used
-  --> $DIR/deriving-smart-pointer-neg.rs:22:31
+  --> $DIR/deriving-smart-pointer-neg.rs:15:31
   |
 LL | struct NoField<'a, #[pointee] T: ?Sized> {}
   |                               ^ unused type parameter
@ -61,7 +75,7 @@ LL | struct NoField<'a, #[pointee] T: ?Sized> {}
   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`

 error[E0392]: lifetime parameter `'a` is never used
-  --> $DIR/deriving-smart-pointer-neg.rs:29:20
+  --> $DIR/deriving-smart-pointer-neg.rs:22:20
   |
 LL | struct NoFieldUnit<'a, #[pointee] T: ?Sized>();
   |                    ^^ unused lifetime parameter
@ -69,13 +83,13 @@ LL | struct NoFieldUnit<'a, #[pointee] T: ?Sized>();
   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`

 error[E0392]: type parameter `T` is never used
-  --> $DIR/deriving-smart-pointer-neg.rs:29:35
+  --> $DIR/deriving-smart-pointer-neg.rs:22:35
   |
 LL | struct NoFieldUnit<'a, #[pointee] T: ?Sized>();
   |                                   ^ unused type parameter
   |
   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`

-error: aborting due to 10 previous errors
+error: aborting due to 12 previous errors

 For more information about this error, try `rustc --explain E0392`.