Auto merge of #134640 - matthiaskrgr:rollup-xlstm3o, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #134364 (Use E0665 for missing `#[default]` on enum and update doc)
 - #134601 (Support pretty-printing `dyn*` trait objects)
 - #134603 (Explain why a type is not eligible for `impl PointerLike`.)
 - #134618 (coroutine_clone: add comments)
 - #134630 (Use `&raw` for `ptr` primitive docs)
 - #134637 (Flatten effects directory now that it doesn't really test anything specific)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1204,8 +1204,10 @@ impl<'a> State<'a> {
             }
             ast::TyKind::Path(Some(qself), path) => self.print_qpath(path, qself, false),
             ast::TyKind::TraitObject(bounds, syntax) => {
-                if *syntax == ast::TraitObjectSyntax::Dyn {
-                    self.word_nbsp("dyn");
+                match syntax {
+                    ast::TraitObjectSyntax::Dyn => self.word_nbsp("dyn"),
+                    ast::TraitObjectSyntax::DynStar => self.word_nbsp("dyn*"),
+                    ast::TraitObjectSyntax::None => {}
                 }
                 self.print_type_bounds(bounds);
             }

compiler/rustc_builtin_macros/messages.ftl

@@ -249,9 +249,9 @@ builtin_macros_naked_functions_testing_attribute =
     .label = function marked with testing attribute here
     .naked_attribute = `#[naked]` is incompatible with testing attributes
 
-builtin_macros_no_default_variant = no default declared
-    .help = make a unit variant default by placing `#[default]` above it
-    .suggestion = make `{$ident}` default
+builtin_macros_no_default_variant = `#[derive(Default)]` on enum with no `#[default]`
+    .label = this enum needs a unit variant marked with `#[default]`
+    .suggestion = make this unit variant default by placing `#[default]` on it
 
 builtin_macros_non_abi = at least one abi must be provided as an argument to `clobber_abi`
 

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -42,7 +42,9 @@ pub(crate) fn expand_deriving_default(
                     StaticStruct(_, fields) => {
                         default_struct_substructure(cx, trait_span, substr, fields)
                     }
-                    StaticEnum(enum_def, _) => default_enum_substructure(cx, trait_span, enum_def),
+                    StaticEnum(enum_def, _) => {
+                        default_enum_substructure(cx, trait_span, enum_def, item.span())
+                    }
                     _ => cx.dcx().span_bug(trait_span, "method in `derive(Default)`"),
                 }
             })),
@@ -96,9 +98,10 @@ fn default_enum_substructure(
     cx: &ExtCtxt<'_>,
     trait_span: Span,
     enum_def: &EnumDef,
+    item_span: Span,
 ) -> BlockOrExpr {
     let expr = match try {
-        let default_variant = extract_default_variant(cx, enum_def, trait_span)?;
+        let default_variant = extract_default_variant(cx, enum_def, trait_span, item_span)?;
         validate_default_attribute(cx, default_variant)?;
         default_variant
     } {
@@ -146,6 +149,7 @@ fn extract_default_variant<'a>(
     cx: &ExtCtxt<'_>,
     enum_def: &'a EnumDef,
     trait_span: Span,
+    item_span: Span,
 ) -> Result<&'a rustc_ast::Variant, ErrorGuaranteed> {
     let default_variants: SmallVec<[_; 1]> = enum_def
         .variants
@@ -163,9 +167,10 @@ fn extract_default_variant<'a>(
                 .filter(|variant| !attr::contains_name(&variant.attrs, sym::non_exhaustive));
 
             let suggs = possible_defaults
-                .map(|v| errors::NoDefaultVariantSugg { span: v.span, ident: v.ident })
+                .map(|v| errors::NoDefaultVariantSugg { span: v.span.shrink_to_lo() })
                 .collect();
-            let guar = cx.dcx().emit_err(errors::NoDefaultVariant { span: trait_span, suggs });
+            let guar =
+                cx.dcx().emit_err(errors::NoDefaultVariant { span: trait_span, item_span, suggs });
 
             return Err(guar);
         }

compiler/rustc_builtin_macros/src/errors.rs

@@ -369,26 +369,21 @@ pub(crate) struct DerivePathArgsValue {
 }
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_no_default_variant)]
-#[help]
+#[diag(builtin_macros_no_default_variant, code = E0665)]
 pub(crate) struct NoDefaultVariant {
     #[primary_span]
     pub(crate) span: Span,
+    #[label]
+    pub(crate) item_span: Span,
     #[subdiagnostic]
     pub(crate) suggs: Vec<NoDefaultVariantSugg>,
 }
 
 #[derive(Subdiagnostic)]
-#[suggestion(
-    builtin_macros_suggestion,
-    code = "#[default] {ident}",
-    applicability = "maybe-incorrect",
-    style = "tool-only"
-)]
+#[suggestion(builtin_macros_suggestion, code = "#[default] ", applicability = "maybe-incorrect")]
 pub(crate) struct NoDefaultVariantSugg {
     #[primary_span]
     pub(crate) span: Span,
-    pub(crate) ident: Ident,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_error_codes/src/error_codes/E0665.md

@@ -1,10 +1,9 @@
-#### Note: this error code is no longer emitted by the compiler.
-
-The `Default` trait was derived on an enum.
+The `Default` trait was derived on an enum without specifying the default
+variant.
 
 Erroneous code example:
 
-```compile_fail
+```compile_fail,E0665
 #[derive(Default)]
 enum Food {
     Sweet,
@@ -16,18 +15,30 @@ The `Default` cannot be derived on an enum for the simple reason that the
 compiler doesn't know which value to pick by default whereas it can for a
 struct as long as all its fields implement the `Default` trait as well.
 
-If you still want to implement `Default` on your enum, you'll have to do it "by
-hand":
+For the case where the desired default variant has no payload, you can
+annotate it with `#[default]` to derive it:
 
 ```
+#[derive(Default)]
 enum Food {
+    #[default]
     Sweet,
     Salty,
 }
+```
+
+In the case where the default variant does have a payload, you will have to
+implement `Default` on your enum manually:
+
+```
+enum Food {
+    Sweet(i32),
+    Salty,
+}
 
 impl Default for Food {
     fn default() -> Food {
-        Food::Sweet
+        Food::Sweet(1)
     }
 }
 ```

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -673,37 +673,6 @@ fn visit_implementation_of_pointer_like(checker: &Checker<'_>) -> Result<(), Err
     let impl_span = tcx.def_span(checker.impl_def_id);
     let self_ty = tcx.impl_trait_ref(checker.impl_def_id).unwrap().instantiate_identity().self_ty();
 
-    // If an ADT is repr(transparent)...
-    if let ty::Adt(def, args) = *self_ty.kind()
-        && def.repr().transparent()
-    {
-        // FIXME(compiler-errors): This should and could be deduplicated into a query.
-        // Find the nontrivial field.
-        let adt_typing_env = ty::TypingEnv::non_body_analysis(tcx, def.did());
-        let nontrivial_field = def.all_fields().find(|field_def| {
-            let field_ty = tcx.type_of(field_def.did).instantiate_identity();
-            !tcx.layout_of(adt_typing_env.as_query_input(field_ty))
-                .is_ok_and(|layout| layout.layout.is_1zst())
-        });
-
-        if let Some(nontrivial_field) = nontrivial_field {
-            // Check that the nontrivial field implements `PointerLike`.
-            let nontrivial_field = nontrivial_field.ty(tcx, args);
-            let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
-            let ocx = ObligationCtxt::new(&infcx);
-            ocx.register_bound(
-                ObligationCause::misc(impl_span, checker.impl_def_id),
-                param_env,
-                nontrivial_field,
-                tcx.lang_items().pointer_like().unwrap(),
-            );
-            // FIXME(dyn-star): We should regionck this implementation.
-            if ocx.select_all_or_error().is_empty() {
-                return Ok(());
-            }
-        }
-    }
-
     let is_permitted_primitive = match *self_ty.kind() {
         ty::Adt(def, _) => def.is_box(),
         ty::Uint(..) | ty::Int(..) | ty::RawPtr(..) | ty::Ref(..) | ty::FnPtr(..) => true,
@@ -717,12 +686,81 @@ fn visit_implementation_of_pointer_like(checker: &Checker<'_>) -> Result<(), Err
         return Ok(());
     }
 
+    let why_disqualified = match *self_ty.kind() {
+        // If an ADT is repr(transparent)
+        ty::Adt(self_ty_def, args) => {
+            if self_ty_def.repr().transparent() {
+                // FIXME(compiler-errors): This should and could be deduplicated into a query.
+                // Find the nontrivial field.
+                let adt_typing_env = ty::TypingEnv::non_body_analysis(tcx, self_ty_def.did());
+                let nontrivial_field = self_ty_def.all_fields().find(|field_def| {
+                    let field_ty = tcx.type_of(field_def.did).instantiate_identity();
+                    !tcx.layout_of(adt_typing_env.as_query_input(field_ty))
+                        .is_ok_and(|layout| layout.layout.is_1zst())
+                });
+
+                if let Some(nontrivial_field) = nontrivial_field {
+                    // Check that the nontrivial field implements `PointerLike`.
+                    let nontrivial_field_ty = nontrivial_field.ty(tcx, args);
+                    let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
+                    let ocx = ObligationCtxt::new(&infcx);
+                    ocx.register_bound(
+                        ObligationCause::misc(impl_span, checker.impl_def_id),
+                        param_env,
+                        nontrivial_field_ty,
+                        tcx.lang_items().pointer_like().unwrap(),
+                    );
+                    // FIXME(dyn-star): We should regionck this implementation.
+                    if ocx.select_all_or_error().is_empty() {
+                        return Ok(());
+                    } else {
+                        format!(
+                            "the field `{field_name}` of {descr} `{self_ty}` \
+                    does not implement `PointerLike`",
+                            field_name = nontrivial_field.name,
+                            descr = self_ty_def.descr()
+                        )
+                    }
+                } else {
+                    format!(
+                        "the {descr} `{self_ty}` is `repr(transparent)`, \
+                but does not have a non-trivial field (it is zero-sized)",
+                        descr = self_ty_def.descr()
+                    )
+                }
+            } else if self_ty_def.is_box() {
+                // If we got here, then the `layout.is_pointer_like()` check failed
+                // and this box is not a thin pointer.
+
+                String::from("boxes of dynamically-sized types are too large to be `PointerLike`")
+            } else {
+                format!(
+                    "the {descr} `{self_ty}` is not `repr(transparent)`",
+                    descr = self_ty_def.descr()
+                )
+            }
+        }
+        ty::Ref(..) => {
+            // If we got here, then the `layout.is_pointer_like()` check failed
+            // and this reference is not a thin pointer.
+            String::from("references to dynamically-sized types are too large to be `PointerLike`")
+        }
+        ty::Dynamic(..) | ty::Foreign(..) => {
+            String::from("types of dynamic or unknown size may not implement `PointerLike`")
+        }
+        _ => {
+            // This is a white lie; it is true everywhere outside the standard library.
+            format!("only user-defined sized types are eligible for `impl PointerLike`")
+        }
+    };
+
     Err(tcx
         .dcx()
         .struct_span_err(
             impl_span,
             "implementation must be applied to type that has the same ABI as a pointer, \
             or is `repr(transparent)` and whose field is `PointerLike`",
         )
+        .with_note(why_disqualified)
         .emit())
 }

compiler/rustc_hir_pretty/src/lib.rs

@@ -402,8 +402,10 @@ impl<'a> State<'a> {
             }
             hir::TyKind::Path(ref qpath) => self.print_qpath(qpath, false),
             hir::TyKind::TraitObject(bounds, lifetime, syntax) => {
-                if syntax == ast::TraitObjectSyntax::Dyn {
-                    self.word_space("dyn");
+                match syntax {
+                    ast::TraitObjectSyntax::Dyn => self.word_nbsp("dyn"),
+                    ast::TraitObjectSyntax::DynStar => self.word_nbsp("dyn*"),
+                    ast::TraitObjectSyntax::None => {}
                 }
                 let mut first = true;
                 for bound in bounds {

compiler/rustc_middle/src/mir/syntax.rs

@@ -821,6 +821,11 @@ pub enum TerminatorKind<'tcx> {
     /// continues at the `resume` basic block, with the second argument written to the `resume_arg`
     /// place. If the coroutine is dropped before then, the `drop` basic block is invoked.
     ///
+    /// Note that coroutines can be (unstably) cloned under certain conditions, which means that
+    /// this terminator can **return multiple times**! MIR optimizations that reorder code into
+    /// different basic blocks needs to be aware of that.
+    /// See <https://github.com/rust-lang/rust/issues/95360>.
+    ///
     /// Not permitted in bodies that are not coroutine bodies, or after coroutine lowering.
     ///
     /// **Needs clarification**: What about the evaluation order of the `resume_arg` and `value`?

library/core/src/primitive_docs.rs

@@ -563,11 +563,11 @@ impl () {}
 /// Note that here the call to [`drop`] is for clarity - it indicates
 /// that we are done with the given value and it should be destroyed.
 ///
-/// ## 3. Create it using `ptr::addr_of!`
+/// ## 3. Create it using `&raw`
 ///
-/// Instead of coercing a reference to a raw pointer, you can use the macros
-/// [`ptr::addr_of!`] (for `*const T`) and [`ptr::addr_of_mut!`] (for `*mut T`).
-/// These macros allow you to create raw pointers to fields to which you cannot
+/// Instead of coercing a reference to a raw pointer, you can use the raw borrow
+/// operators `&raw const` (for `*const T`) and `&raw mut` (for `*mut T`).
+/// These operators allow you to create raw pointers to fields to which you cannot
 /// create a reference (without causing undefined behavior), such as an
 /// unaligned field. This might be necessary if packed structs or uninitialized
 /// memory is involved.
@@ -580,7 +580,7 @@ impl () {}
 ///     unaligned: u32,
 /// }
 /// let s = S::default();
-/// let p = std::ptr::addr_of!(s.unaligned); // not allowed with coercion
+/// let p = &raw const s.unaligned; // not allowed with coercion
 /// ```
 ///
 /// ## 4. Get it from C.

tests/ui-fulldeps/pprust-parenthesis-insertion.rs

@@ -135,10 +135,6 @@ static EXPRS: &[&str] = &[
     "(0.).to_string()",
     "0. .. 1.",
     */
-    /*
-    // FIXME: pretty-printer loses the dyn*. `i as Trait`
-    "i as dyn* Trait",
-    */
 ];
 
 // Flatten the content of parenthesis nodes into their parent node. For example

tests/ui/coroutine/clone-impl-static.rs

@@ -1,6 +1,8 @@
 //@compile-flags: --diagnostic-width=300
 // gate-test-coroutine_clone
 // Verifies that static coroutines cannot be cloned/copied.
+// This is important: the cloned coroutine would reference state of the original
+// coroutine, leading to semantic nonsense.
 
 #![feature(coroutines, coroutine_clone, stmt_expr_attributes)]
 

tests/ui/coroutine/clone-impl-static.stderr

@@ -1,27 +1,27 @@
-error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}: Copy` is not satisfied
-  --> $DIR/clone-impl-static.rs:12:16
+error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}: Copy` is not satisfied
+  --> $DIR/clone-impl-static.rs:14:16
    |
 LL |     check_copy(&gen);
-   |     ---------- ^^^^ the trait `Copy` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}`
+   |     ---------- ^^^^ the trait `Copy` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}`
    |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `check_copy`
-  --> $DIR/clone-impl-static.rs:18:18
+  --> $DIR/clone-impl-static.rs:20:18
    |
 LL | fn check_copy<T: Copy>(_x: &T) {}
    |                  ^^^^ required by this bound in `check_copy`
 
-error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}: Clone` is not satisfied
-  --> $DIR/clone-impl-static.rs:14:17
+error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}: Clone` is not satisfied
+  --> $DIR/clone-impl-static.rs:16:17
    |
 LL |     check_clone(&gen);
-   |     ----------- ^^^^ the trait `Clone` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}`
+   |     ----------- ^^^^ the trait `Clone` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}`
    |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `check_clone`
-  --> $DIR/clone-impl-static.rs:19:19
+  --> $DIR/clone-impl-static.rs:21:19
    |
 LL | fn check_clone<T: Clone>(_x: &T) {}
    |                   ^^^^^ required by this bound in `check_clone`