rustdoc: Use own logic to print #[repr(..)] attributes in JSON output.

src/librustdoc/clean/types.rs

@@ -768,12 +768,22 @@ impl Item {
             .iter()
             .filter_map(|attr| {
                 if is_json {
-                    if matches!(attr, hir::Attribute::Parsed(AttributeKind::Deprecation { .. })) {
-                        // rustdoc-json stores this in `Item::deprecation`, so we
-                        // don't want it it `Item::attrs`.
-                        None
-                    } else {
-                        Some(rustc_hir_pretty::attribute_to_string(&tcx, attr))
+                    match attr {
+                        hir::Attribute::Parsed(AttributeKind::Deprecation { .. }) => {
+                            // rustdoc-json stores this in `Item::deprecation`, so we
+                            // don't want it it `Item::attrs`.
+                            None
+                        }
+                        rustc_hir::Attribute::Parsed(rustc_attr_parsing::AttributeKind::Repr(
+                            ..,
+                        )) => {
+                            // We have separate pretty-printing logic for `#[repr(..)]` attributes.
+                            // For example, there are circumstances where `#[repr(transparent)]`
+                            // is applied but should not be publicly shown in rustdoc
+                            // because it isn't public API.
+                            None
+                        }
+                        _ => Some(rustc_hir_pretty::attribute_to_string(&tcx, attr)),
                     }
                 } else if ALLOWED_ATTRIBUTES.contains(&attr.name_or_empty()) {
                     Some(
@@ -789,8 +799,7 @@ impl Item {
             .collect();
 
         // Add #[repr(...)]
-        if !is_json
-            && let Some(def_id) = self.def_id()
+        if let Some(def_id) = self.def_id()
             && let ItemType::Struct | ItemType::Enum | ItemType::Union = self.type_()
         {
             let adt = tcx.adt_def(def_id);

src/rustdoc-json-types/lib.rs

@@ -30,7 +30,7 @@ pub type FxHashMap<K, V> = HashMap<K, V>; // re-export for use in src/librustdoc
 /// This integer is incremented with every breaking change to the API,
 /// and is returned along with the JSON blob as [`Crate::format_version`].
 /// Consuming code should assert that this value matches the format version(s) that it supports.
-pub const FORMAT_VERSION: u32 = 42;
+pub const FORMAT_VERSION: u32 = 43;
 
 /// The root of the emitted JSON blob.
 ///
@@ -120,9 +120,23 @@ pub struct Item {
     pub docs: Option<String>,
     /// This mapping resolves [intra-doc links](https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md) from the docstring to their IDs
     pub links: HashMap<String, Id>,
-    /// Stringified versions of parsed attributes on this item.
-    /// Essentially debug printed (e.g. `#[inline]` becomes something similar to `#[attr="Inline(Hint)"]`).
-    /// Equivalent to the hir pretty-printing of attributes.
+    /// Attributes on this item.
+    ///
+    /// Does not include `#[deprecated]` attributes: see the [`Self::deprecation`] field instead.
+    ///
+    /// Some attributes appear in pretty-printed Rust form, regardless of their formatting
+    /// in the original source code. For example:
+    /// - `#[non_exhaustive]` and `#[must_use]` are represented as themselves.
+    /// - `#[no_mangle]` and `#[export_name]` are also represented as themselves.
+    /// - `#[repr(C)]` and other reprs also appear as themselves,
+    ///   though potentially with a different order: e.g. `repr(i8, C)` may become `repr(C, i8)`.
+    ///   Multiple repr attributes on the same item may be combined into an equivalent single attr.
+    ///
+    /// Other attributes may appear debug-printed. For example:
+    /// - `#[inline]` becomes something similar to `#[attr="Inline(Hint)"]`.
+    ///
+    /// As an internal implementation detail subject to change, this debug-printing format
+    /// is currently equivalent to the HIR pretty-printing of parsed attributes.
     pub attrs: Vec<String>,
     /// Information about the item’s deprecation, if present.
     pub deprecation: Option<Deprecation>,

tests/rustdoc-json/attrs/repr_align.rs

@@ -1,6 +1,6 @@
 #![no_std]
 
-//@ is "$.index[?(@.name=='Aligned')].attrs" '["#[attr = Repr([ReprAlign(Align(4 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='Aligned')].attrs" '["#[repr(align(4))]"]'
 #[repr(align(4))]
 pub struct Aligned {
     a: i8,

tests/rustdoc-json/attrs/repr_c.rs

@@ -1,16 +1,16 @@
 #![no_std]
 
-//@ is "$.index[?(@.name=='ReprCStruct')].attrs" '["#[attr = Repr([ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReprCStruct')].attrs" '["#[repr(C)]"]'
 #[repr(C)]
 pub struct ReprCStruct(pub i64);
 
-//@ is "$.index[?(@.name=='ReprCEnum')].attrs" '["#[attr = Repr([ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReprCEnum')].attrs" '["#[repr(C)]"]'
 #[repr(C)]
 pub enum ReprCEnum {
     First,
 }
 
-//@ is "$.index[?(@.name=='ReprCUnion')].attrs" '["#[attr = Repr([ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReprCUnion')].attrs" '["#[repr(C)]"]'
 #[repr(C)]
 pub union ReprCUnion {
     pub left: i64,

tests/rustdoc-json/attrs/repr_combination.rs

@@ -1,77 +1,78 @@
 #![no_std]
 
 // Combinations of `#[repr(..)]` attributes.
+// Rustdoc JSON emits normalized output, regardless of the original source.
 
-//@ is "$.index[?(@.name=='ReprCI8')].attrs" '["#[attr = Repr([ReprC, ReprInt(SignedInt(I8))])]\n"]'
+//@ is "$.index[?(@.name=='ReprCI8')].attrs" '["#[repr(C, i8)]"]'
 #[repr(C, i8)]
 pub enum ReprCI8 {
     First,
 }
 
-//@ is "$.index[?(@.name=='SeparateReprCI16')].attrs" '["#[attr = Repr([ReprC, ReprInt(SignedInt(I16))])]\n"]'
+//@ is "$.index[?(@.name=='SeparateReprCI16')].attrs" '["#[repr(C, i16)]"]'
 #[repr(C)]
 #[repr(i16)]
 pub enum SeparateReprCI16 {
     First,
 }
 
-//@ is "$.index[?(@.name=='ReversedReprCUsize')].attrs" '["#[attr = Repr([ReprInt(UnsignedInt(Usize)), ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReversedReprCUsize')].attrs" '["#[repr(C, usize)]"]'
 #[repr(usize, C)]
 pub enum ReversedReprCUsize {
     First,
 }
 
-//@ is "$.index[?(@.name=='ReprCPacked')].attrs" '["#[attr = Repr([ReprC, ReprPacked(Align(1 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='ReprCPacked')].attrs" '["#[repr(C, packed(1))]"]'
 #[repr(C, packed)]
 pub struct ReprCPacked {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='SeparateReprCPacked')].attrs" '["#[attr = Repr([ReprC, ReprPacked(Align(2 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='SeparateReprCPacked')].attrs" '["#[repr(C, packed(2))]"]'
 #[repr(C)]
 #[repr(packed(2))]
 pub struct SeparateReprCPacked {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='ReversedReprCPacked')].attrs" '["#[attr = Repr([ReprPacked(Align(2 bytes)), ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReversedReprCPacked')].attrs" '["#[repr(C, packed(2))]"]'
 #[repr(packed(2), C)]
 pub struct ReversedReprCPacked {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='ReprCAlign')].attrs" '["#[attr = Repr([ReprC, ReprAlign(Align(16 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='ReprCAlign')].attrs" '["#[repr(C, align(16))]"]'
 #[repr(C, align(16))]
 pub struct ReprCAlign {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='SeparateReprCAlign')].attrs" '["#[attr = Repr([ReprC, ReprAlign(Align(2 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='SeparateReprCAlign')].attrs" '["#[repr(C, align(2))]"]'
 #[repr(C)]
 #[repr(align(2))]
 pub struct SeparateReprCAlign {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='ReversedReprCAlign')].attrs" '["#[attr = Repr([ReprAlign(Align(2 bytes)), ReprC])]\n"]'
+//@ is "$.index[?(@.name=='ReversedReprCAlign')].attrs" '["#[repr(C, align(2))]"]'
 #[repr(align(2), C)]
 pub struct ReversedReprCAlign {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='AlignedExplicitRepr')].attrs" '["#[attr = Repr([ReprC, ReprAlign(Align(16 bytes)), ReprInt(SignedInt(Isize))])]\n"]'
+//@ is "$.index[?(@.name=='AlignedExplicitRepr')].attrs" '["#[repr(C, align(16), isize)]"]'
 #[repr(C, align(16), isize)]
 pub enum AlignedExplicitRepr {
     First,
 }
 
-//@ is "$.index[?(@.name=='ReorderedAlignedExplicitRepr')].attrs" '["#[attr = Repr([ReprInt(SignedInt(Isize)), ReprC, ReprAlign(Align(16 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='ReorderedAlignedExplicitRepr')].attrs" '["#[repr(C, align(16), isize)]"]'
 #[repr(isize, C, align(16))]
 pub enum ReorderedAlignedExplicitRepr {
     First,

tests/rustdoc-json/attrs/repr_int_enum.rs

@@ -1,18 +1,18 @@
 #![no_std]
 
-//@ is "$.index[?(@.name=='I8')].attrs" '["#[attr = Repr([ReprInt(SignedInt(I8))])]\n"]'
+//@ is "$.index[?(@.name=='I8')].attrs" '["#[repr(i8)]"]'
 #[repr(i8)]
 pub enum I8 {
     First,
 }
 
-//@ is "$.index[?(@.name=='I32')].attrs" '["#[attr = Repr([ReprInt(SignedInt(I32))])]\n"]'
+//@ is "$.index[?(@.name=='I32')].attrs" '["#[repr(i32)]"]'
 #[repr(i32)]
 pub enum I32 {
     First,
 }
 
-//@ is "$.index[?(@.name=='Usize')].attrs" '["#[attr = Repr([ReprInt(UnsignedInt(Usize))])]\n"]'
+//@ is "$.index[?(@.name=='Usize')].attrs" '["#[repr(usize)]"]'
 #[repr(usize)]
 pub enum Usize {
     First,

tests/rustdoc-json/attrs/repr_packed.rs

@@ -1,16 +1,16 @@
 #![no_std]
 
 // Note the normalization:
-// `#[repr(packed)]` in has the implict "1" in rustdoc JSON.
-
-//@ is "$.index[?(@.name=='Packed')].attrs" '["#[attr = Repr([ReprPacked(Align(1 bytes))])]\n"]'
+// `#[repr(packed)]` in source becomes `#[repr(packed(1))]` in rustdoc JSON.
+//
+//@ is "$.index[?(@.name=='Packed')].attrs" '["#[repr(packed(1))]"]'
 #[repr(packed)]
 pub struct Packed {
     a: i8,
     b: i64,
 }
 
-//@ is "$.index[?(@.name=='PackedAligned')].attrs" '["#[attr = Repr([ReprPacked(Align(4 bytes))])]\n"]'
+//@ is "$.index[?(@.name=='PackedAligned')].attrs" '["#[repr(packed(4))]"]'
 #[repr(packed(4))]
 pub struct PackedAligned {
     a: i8,

tests/rustdoc-json/attrs/repr_transparent.rs

@@ -1,22 +1,37 @@
 #![no_std]
 
-// Rustdoc JSON currently includes `#[repr(transparent)]`
-// even if the transparency is not part of the public API
+// Rustdoc JSON *only* includes `#[repr(transparent)]`
+// if the transparency is public API:
+// - if a non-1-ZST field exists, it has to be public
+// - otherwise, all fields are 1-ZST and at least one of them is public
 //
-// https://doc.rust-lang.org/nomicon/other-reprs.html#reprtransparent
+// More info: https://doc.rust-lang.org/nomicon/other-reprs.html#reprtransparent
 
-//@ is "$.index[?(@.name=='Transparent')].attrs" '["#[attr = Repr([ReprTransparent])]\n"]'
+// Here, the non-1-ZST field is public.
+// We expect `#[repr(transparent)]` in the attributes.
+//
+//@ is "$.index[?(@.name=='Transparent')].attrs" '["#[repr(transparent)]"]'
 #[repr(transparent)]
 pub struct Transparent(pub i64);
 
-//@ is "$.index[?(@.name=='TransparentNonPub')].attrs" '["#[attr = Repr([ReprTransparent])]\n"]'
+// Here the non-1-ZST field isn't public, so the attribute isn't included.
+//
+//@ has "$.index[?(@.name=='TransparentNonPub')]"
+//@ is "$.index[?(@.name=='TransparentNonPub')].attrs" '[]'
 #[repr(transparent)]
 pub struct TransparentNonPub(i64);
 
-//@ is "$.index[?(@.name=='AllZst')].attrs" '["#[attr = Repr([ReprTransparent])]\n"]'
+// Only 1-ZST fields here, and one of them is public.
+// We expect `#[repr(transparent)]` in the attributes.
+//
+//@ is "$.index[?(@.name=='AllZst')].attrs" '["#[repr(transparent)]"]'
 #[repr(transparent)]
 pub struct AllZst<'a>(pub core::marker::PhantomData<&'a ()>, ());
 
-//@ is "$.index[?(@.name=='AllZstNotPublic')].attrs" '["#[attr = Repr([ReprTransparent])]\n"]'
+// Only 1-ZST fields here but none of them are public.
+// The attribute isn't included.
+//
+//@ has "$.index[?(@.name=='AllZstNotPublic')]"
+//@ is "$.index[?(@.name=='AllZstNotPublic')].attrs" '[]'
 #[repr(transparent)]
 pub struct AllZstNotPublic<'a>(core::marker::PhantomData<&'a ()>, ());

tests/rustdoc-json/enums/discriminant/struct.rs

@@ -1,5 +1,5 @@
 #[repr(i32)]
-//@ is "$.index[?(@.name=='Foo')].attrs" '["#[attr = Repr([ReprInt(SignedInt(I32))])]\n"]'
+//@ is "$.index[?(@.name=='Foo')].attrs" '["#[repr(i32)]"]'
 pub enum Foo {
     //@ is    "$.index[?(@.name=='Struct')].inner.variant.discriminant" null
     //@ count "$.index[?(@.name=='Struct')].inner.variant.kind.struct.fields[*]" 0

tests/rustdoc-json/enums/discriminant/tuple.rs

@@ -1,5 +1,5 @@
 #[repr(u32)]
-//@ is "$.index[?(@.name=='Foo')].attrs" '["#[attr = Repr([ReprInt(UnsignedInt(U32))])]\n"]'
+//@ is "$.index[?(@.name=='Foo')].attrs" '["#[repr(u32)]"]'
 pub enum Foo {
     //@ is    "$.index[?(@.name=='Tuple')].inner.variant.discriminant" null
     //@ count "$.index[?(@.name=='Tuple')].inner.variant.kind.tuple[*]" 0