[rustdoc-json] Suppress ?Sized bounds from rustdoc when Sized is implied.

obi1kenobi · obi1kenobi · commit 85e32ef70ed0 · 2025-08-20T03:33:39.000Z
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
@@ -548,12 +548,15 @@ fn clean_generic_param_def(
             } else {
                 None
             };
+            let param_ty = ty::ParamTy::for_def(def);
+            let allow_unsized = !param_ty.to_ty(cx.tcx).is_sized(cx.tcx, cx.typing_env());
             (
                 def.name,
                 GenericParamDefKind::Type {
                     bounds: ThinVec::new(), // These are filled in from the where-clauses.
                     default: default.map(Box::new),
                     synthetic,
+                    allow_unsized,
                 },
             )
         }
@@ -627,12 +630,38 @@ fn clean_generic_param<'tcx>(
             } else {
                 ThinVec::new()
             };
+
+            // If this ends up being slow, then optimize it by reading the local bounds
+            // (from all predicate origins) and check if a bound on `?Sized` is present.
+            // If there's no `?Sized` bound, then definitely `allow_unsized = false`.
+            let allow_unsized = {
+                let parent = cx.tcx.hir_ty_param_owner(param.def_id);
+                let index = cx
+                    .tcx
+                    .generics_of(parent)
+                    .param_def_id_to_index(cx.tcx, param.def_id.to_def_id());
+
+                if let Some(index) = index {
+                    let param_ty = ty::ParamTy::new(index, param.name.ident().name);
+                    !param_ty.to_ty(cx.tcx).is_sized(cx.tcx, cx.typing_env())
+                } else {
+                    // The type is introduced by a `for<T>` binder.
+                    // This is an unstable, incomplete feature
+                    // gated behind `#![feature(non_lifetime_binders)]`.
+                    //
+                    // When the details of `for<T>` are worked out and
+                    // the feature is closer to stabilization, add appropriate logic here.
+                    false
+                }
+            };
+
             (
                 param.name.ident().name,
                 GenericParamDefKind::Type {
                     bounds,
                     default: default.map(|t| clean_ty(t, cx)).map(Box::new),
                     synthetic,
+                    allow_unsized,
                 },
             )
         }
@@ -3210,6 +3239,7 @@ fn clean_bound_vars<'tcx>(
                         bounds: ThinVec::new(),
                         default: None,
                         synthetic: false,
+                        allow_unsized: false, // If `for<T>` could support `T: ?Sized`, fix this.
                     },
                 })
             }
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
@@ -1357,10 +1357,21 @@ impl WherePredicate {
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub(crate) enum GenericParamDefKind {
-    Lifetime { outlives: ThinVec<Lifetime> },
-    Type { bounds: ThinVec<GenericBound>, default: Option<Box<Type>>, synthetic: bool },
+    Lifetime {
+        outlives: ThinVec<Lifetime>,
+    },
+    Type {
+        bounds: ThinVec<GenericBound>,
+        default: Option<Box<Type>>,
+        synthetic: bool,
+        allow_unsized: bool,
+    },
     // Option<Box<String>> makes this type smaller than `Option<String>` would.
-    Const { ty: Box<Type>, default: Option<Box<String>>, synthetic: bool },
+    Const {
+        ty: Box<Type>,
+        default: Option<Box<String>>,
+        synthetic: bool,
+    },
 }
 
 impl GenericParamDefKind {
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
@@ -458,10 +458,11 @@ impl FromClean<clean::GenericParamDefKind> for GenericParamDefKind {
             Lifetime { outlives } => {
                 GenericParamDefKind::Lifetime { outlives: outlives.into_json(renderer) }
             }
-            Type { bounds, default, synthetic } => GenericParamDefKind::Type {
+            Type { bounds, default, synthetic, allow_unsized } => GenericParamDefKind::Type {
                 bounds: bounds.into_json(renderer),
                 default: default.into_json(renderer),
                 is_synthetic: *synthetic,
+                allow_unsized: *allow_unsized,
             },
             Const { ty, default, synthetic: _ } => GenericParamDefKind::Const {
                 type_: ty.into_json(renderer),
diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
@@ -37,8 +37,8 @@ pub type FxHashMap<K, V> = HashMap<K, V>; // re-export for use in src/librustdoc
 // will instead cause conflicts. See #94591 for more. (This paragraph and the "Latest feature" line
 // are deliberately not in a doc comment, because they need not be in public docs.)
 //
-// Latest feature: Add Attribute::MacroUse
-pub const FORMAT_VERSION: u32 = 55;
+// Latest feature: Add `allow_unsized` field to `GenericParamDefKind::Type`
+pub const FORMAT_VERSION: u32 = 56;
 
 /// The root of the emitted JSON blob.
 ///
@@ -977,6 +977,11 @@ pub enum GenericParamDefKind {
         /// is bound by `Trait`) is synthetic, because it was not originally in
         /// the Rust source text.
         is_synthetic: bool,
+        /// Whether this type parameter can be instantiated with an unsized type.
+        ///
+        /// This is `true` if the parameter has a `?Sized` bound without any
+        /// additional bounds that imply `Sized`.
+        allow_unsized: bool,
     },
 
     /// Denotes a constant parameter.
diff --git a/src/tools/jsondoclint/src/validator.rs b/src/tools/jsondoclint/src/validator.rs
@@ -332,7 +332,12 @@ impl<'a> Validator<'a> {
     fn check_generic_param_def(&mut self, gpd: &'a GenericParamDef) {
         match &gpd.kind {
             rustdoc_json_types::GenericParamDefKind::Lifetime { outlives: _ } => {}
-            rustdoc_json_types::GenericParamDefKind::Type { bounds, default, is_synthetic: _ } => {
+            rustdoc_json_types::GenericParamDefKind::Type {
+                bounds,
+                default,
+                is_synthetic: _,
+                allow_unsized: _,
+            } => {
                 bounds.iter().for_each(|b| self.check_generic_bound(b));
                 if let Some(ty) = default {
                     self.check_type(ty);
diff --git a/tests/rustdoc-json/allow_unsized.rs b/tests/rustdoc-json/allow_unsized.rs
@@ -0,0 +1,139 @@
+#![crate_name = "allow_unsized"]
+
+use std::fmt::Debug;
+use std::marker::PhantomData;
+
+pub trait CustomSized: Sized {}
+impl CustomSized for u8 {}
+
+// Generic functions
+//@ is "$.index[?(@.name=='func_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn func_custom<T: ?Sized + CustomSized>() {}
+
+//@ is "$.index[?(@.name=='func_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn func_custom_where_denies<T: ?Sized>()
+where
+    T: CustomSized,
+{
+}
+
+//@ is "$.index[?(@.name=='func_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn func_custom_where_allows<T: CustomSized>()
+where
+    T: ?Sized,
+{
+}
+
+//@ is "$.index[?(@.name=='func_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn func_custom_where_both<T>()
+where
+    T: ?Sized + CustomSized,
+{
+}
+
+//@ is "$.index[?(@.name=='func_unsized')].inner.function.generics.params[0].kind.type.allow_unsized" true
+pub fn func_unsized<T: ?Sized>() {}
+
+//@ is "$.index[?(@.name=='func_clone')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn func_clone<T: ?Sized + Clone>() {}
+
+//@ is "$.index[?(@.name=='func_debug')].inner.function.generics.params[0].kind.type.allow_unsized" true
+pub fn func_debug<T: ?Sized + Debug>() {}
+
+// Generic structs
+//@ is "$.index[?(@.name=='StructCustom')].inner.struct.generics.params[0].kind.type.allow_unsized" false
+pub struct StructCustom<T: ?Sized + CustomSized>(PhantomData<T>);
+
+//@ is "$.index[?(@.name=='StructUnsized')].inner.struct.generics.params[0].kind.type.allow_unsized" true
+pub struct StructUnsized<T: ?Sized>(PhantomData<T>);
+
+//@ is "$.index[?(@.name=='StructClone')].inner.struct.generics.params[0].kind.type.allow_unsized" false
+pub struct StructClone<T: ?Sized + Clone>(PhantomData<T>);
+
+//@ is "$.index[?(@.name=='StructDebug')].inner.struct.generics.params[0].kind.type.allow_unsized" true
+pub struct StructDebug<T: ?Sized + Debug>(PhantomData<T>);
+
+// Struct with `?Sized` bound, and impl blocks that add additional bounds
+//@ is "$.index[?(@.name=='Wrapper')].inner.struct.generics.params[0].kind.type.allow_unsized" true
+pub struct Wrapper<T: ?Sized>(PhantomData<T>);
+
+//@ is "$.index[?(@.docs=='impl custom')].inner.impl.generics.params[0].kind.type.allow_unsized" false
+/// impl custom
+impl<T: ?Sized + CustomSized> Wrapper<T> {
+    pub fn impl_custom() {}
+}
+
+//@ is "$.index[?(@.docs=='impl clone')].inner.impl.generics.params[0].kind.type.allow_unsized" false
+/// impl clone
+impl<T: ?Sized + Clone> Wrapper<T> {
+    pub fn impl_clone() {}
+}
+
+//@ is "$.index[?(@.docs=='impl debug')].inner.impl.generics.params[0].kind.type.allow_unsized" true
+/// impl debug
+impl<T: ?Sized + Debug> Wrapper<T> {
+    pub fn impl_debug() {}
+}
+
+impl<T: ?Sized> Wrapper<T> {
+    //@ is "$.index[?(@.name=='assoc_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+    pub fn assoc_custom<U: ?Sized + CustomSized>(&self) {}
+
+    //@ is "$.index[?(@.name=='assoc_unsized')].inner.function.generics.params[0].kind.type.allow_unsized" true
+    pub fn assoc_unsized<U: ?Sized>(&self) {}
+
+    //@ is "$.index[?(@.name=='assoc_clone')].inner.function.generics.params[0].kind.type.allow_unsized" false
+    pub fn assoc_clone<U: ?Sized + Clone>(&self) {}
+
+    //@ is "$.index[?(@.name=='assoc_debug')].inner.function.generics.params[0].kind.type.allow_unsized" true
+    pub fn assoc_debug<U: ?Sized + Debug>(&self) {}
+}
+
+// Traits with generic parameters
+//@ is "$.index[?(@.name=='TraitCustom')].inner.trait.generics.params[0].kind.type.allow_unsized" false
+pub trait TraitCustom<T: ?Sized + CustomSized> {}
+
+//@ is "$.index[?(@.name=='TraitUnsized')].inner.trait.generics.params[0].kind.type.allow_unsized" true
+pub trait TraitUnsized<T: ?Sized> {}
+
+//@ is "$.index[?(@.name=='TraitClone')].inner.trait.generics.params[0].kind.type.allow_unsized" false
+pub trait TraitClone<T: ?Sized + Clone> {}
+
+//@ is "$.index[?(@.name=='TraitDebug')].inner.trait.generics.params[0].kind.type.allow_unsized" true
+pub trait TraitDebug<T: ?Sized + Debug> {}
+
+pub trait TraitMethods {
+    //@ is "$.index[?(@.name=='method_custom')].inner.function.generics.params[0].kind.type.allow_unsized" false
+    fn method_custom<T: ?Sized + CustomSized>();
+
+    //@ is "$.index[?(@.name=='method_unsized')].inner.function.generics.params[0].kind.type.allow_unsized" true
+    fn method_unsized<T: ?Sized>();
+
+    //@ is "$.index[?(@.name=='method_clone')].inner.function.generics.params[0].kind.type.allow_unsized" false
+    fn method_clone<T: ?Sized + Clone>();
+
+    //@ is "$.index[?(@.name=='method_debug')].inner.function.generics.params[0].kind.type.allow_unsized" true
+    fn method_debug<T: ?Sized + Debug>();
+}
+
+// `where` clauses on trait functions, which only affect `T` for that function
+//@ is "$.index[?(@.name=='OuterDebug')].inner.trait.generics.params[0].kind.type.allow_unsized" true
+pub trait OuterDebug<T: ?Sized> {
+    fn foo()
+    where
+        T: Debug;
+}
+
+//@ is "$.index[?(@.name=='OuterClone')].inner.trait.generics.params[0].kind.type.allow_unsized" true
+pub trait OuterClone<T: ?Sized> {
+    fn foo()
+    where
+        T: Clone;
+}
+
+// Synthetic generic parameters
+//@ is "$.index[?(@.name=='synth_clone')].inner.function.generics.params[0].kind.type.allow_unsized" false
+pub fn synth_clone(_: impl Clone + ?Sized) {}
+
+//@ is "$.index[?(@.name=='synth_debug')].inner.function.generics.params[0].kind.type.allow_unsized" true
+pub fn synth_debug(_: impl Debug + ?Sized) {}
diff --git a/tests/rustdoc-json/fns/generic_args.rs b/tests/rustdoc-json/fns/generic_args.rs
@@ -27,7 +27,7 @@ pub fn impl_trait(f: impl Foo) {}
 
 //@ count "$.index[?(@.name=='where_clase')].inner.function.generics.params[*]" 3
 //@ is "$.index[?(@.name=='where_clase')].inner.function.generics.params[0].name" '"F"'
-//@ is "$.index[?(@.name=='where_clase')].inner.function.generics.params[0].kind" '{"type": {"bounds": [], "default": null, "is_synthetic": false}}'
+//@ is "$.index[?(@.name=='where_clase')].inner.function.generics.params[0].kind" '{"type": {"bounds": [], "default": null, "is_synthetic": false, "allow_unsized": false}}'
 //@ count "$.index[?(@.name=='where_clase')].inner.function.sig.inputs[*]" 3
 //@ is "$.index[?(@.name=='where_clase')].inner.function.sig.inputs[0][0]" '"f"'
 //@ is "$.index[?(@.name=='where_clase')].inner.function.sig.inputs[0][1].generic" '"F"'
diff --git a/tests/rustdoc-json/non_lifetime_binders.rs b/tests/rustdoc-json/non_lifetime_binders.rs
@@ -9,7 +9,7 @@ pub struct Wrapper<T_>(std::marker::PhantomData<T_>);
 //@ is "$.index[?(@.name=='foo')].inner.function.generics.where_predicates[0].bound_predicate.generic_params[0].name" \"\'a\"
 //@ is "$.index[?(@.name=='foo')].inner.function.generics.where_predicates[0].bound_predicate.generic_params[0].kind" '{ "lifetime": { "outlives": [] } }'
 //@ is "$.index[?(@.name=='foo')].inner.function.generics.where_predicates[0].bound_predicate.generic_params[1].name" \"T\"
-//@ is "$.index[?(@.name=='foo')].inner.function.generics.where_predicates[0].bound_predicate.generic_params[1].kind" '{ "type": { "bounds": [], "default": null, "is_synthetic": false } }'
+//@ is "$.index[?(@.name=='foo')].inner.function.generics.where_predicates[0].bound_predicate.generic_params[1].kind" '{ "type": { "bounds": [], "default": null, "is_synthetic": false, "allow_unsized": false } }'
 pub fn foo()
 where
     for<'a, T> &'a Wrapper<T>: Trait,
