Rollup of 16 pull requests

Cargo.lock

@@ -6213,9 +6213,9 @@ dependencies = [
 
 [[package]]
 name = "wasi-preview1-component-adapter-provider"
-version = "44.0.2"
+version = "46.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2211ca2d69a88055eefb06bad741dde3180c9d4020f7e42fea72caba83f9c10c"
+checksum = "1b6c48003fe59c201c97a7786ff55feabe6b6f83b598aa9ff5bcc4f94d940bf3"
 
 [[package]]
 name = "wasip2"
@@ -6282,9 +6282,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-component-ld"
-version = "0.5.25"
+version = "0.5.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ee72c06c556db23aca2d29e1e183d96efdffa7110b24915629a5091de600a894"
+checksum = "51a12709376d4ce64f472699500db3b0e5902cc2bef16fb6ca3098bfdac032fa"
 dependencies = [
  "anyhow",
  "clap",
@@ -6293,12 +6293,12 @@ dependencies = [
  "libc",
  "tempfile",
  "wasi-preview1-component-adapter-provider",
- "wasmparser 0.252.0",
+ "wasmparser 0.253.0",
  "wat",
  "windows-sys 0.61.2",
  "winsplit",
- "wit-component 0.252.0",
- "wit-parser 0.252.0",
+ "wit-component 0.253.0",
+ "wit-parser 0.253.0",
 ]
 
 [[package]]
@@ -6330,12 +6330,12 @@ dependencies = [
 
 [[package]]
 name = "wasm-encoder"
-version = "0.252.0"
+version = "0.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8185ae345fa5687c054626ff9a50e7089797a343d9904d1dc9820eb4c4d3196f"
+checksum = "59972d6cd272259de647b7c1f1912e45e289c75ffd4be04e10695507cd7e1b59"
 dependencies = [
  "leb128fmt",
- "wasmparser 0.252.0",
+ "wasmparser 0.253.0",
 ]
 
 [[package]]
@@ -6352,14 +6352,14 @@ dependencies = [
 
 [[package]]
 name = "wasm-metadata"
-version = "0.252.0"
+version = "0.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2b7e08e02a3cd55bf778009d4cd6faae50da011f293644daf78a531a32d6d142"
+checksum = "b3f45816ef616806f48498bcd831377de578c4fa51db0c83ab8ceb78cc13523b"
 dependencies = [
  "anyhow",
  "indexmap",
- "wasm-encoder 0.252.0",
- "wasmparser 0.252.0",
+ "wasm-encoder 0.253.0",
+ "wasmparser 0.253.0",
 ]
 
 [[package]]
@@ -6396,9 +6396,9 @@ dependencies = [
 
 [[package]]
 name = "wasmparser"
-version = "0.252.0"
+version = "0.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d3eb099dcadcde5be9eef55e3a337128efd4e44b4c93122487e4d2e4e1c6627c"
+checksum = "19db11f87d2486580e1e8b6f494c54df7e0566b87d0b599db843c24019667339"
 dependencies = [
  "bitflags",
  "hashbrown 0.17.0",
@@ -6409,22 +6409,22 @@ dependencies = [
 
 [[package]]
 name = "wast"
-version = "252.0.0"
+version = "253.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "942a3449d6a593fccc111a6241c8df52bda168af30e40bf9580d4394d7374c65"
+checksum = "d3264542f8965c5d84fb1085d924bfba9a6314bb228eff13a2de14d7627664d0"
 dependencies = [
  "bumpalo",
  "leb128fmt",
  "memchr",
  "unicode-width 0.2.2",
- "wasm-encoder 0.252.0",
+ "wasm-encoder 0.253.0",
 ]
 
 [[package]]
 name = "wat"
-version = "1.252.0"
+version = "1.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c72a4ba7088f7bac94cf516e49882bdf97068904a563768cf249efc839ec42cb"
+checksum = "4bfc5ce906144200c972ec617470aa35bd847472e170b26dde3e80541c674055"
 dependencies = [
  "wast",
 ]
@@ -6872,9 +6872,9 @@ dependencies = [
 
 [[package]]
 name = "wit-component"
-version = "0.252.0"
+version = "0.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "76db0662b590f45d33d0e363fa13539a5a1eecd35d5a12fe208c335461c1053d"
+checksum = "dbbd2500ac3488489ee8c6e59b79d7e47e6da5bfb019efd35d5dca57b78af624"
 dependencies = [
  "anyhow",
  "bitflags",
@@ -6883,10 +6883,10 @@ dependencies = [
  "serde",
  "serde_derive",
  "serde_json",
- "wasm-encoder 0.252.0",
- "wasm-metadata 0.252.0",
- "wasmparser 0.252.0",
- "wit-parser 0.252.0",
+ "wasm-encoder 0.253.0",
+ "wasm-metadata 0.253.0",
+ "wasmparser 0.253.0",
+ "wit-parser 0.253.0",
 ]
 
 [[package]]
@@ -6909,9 +6909,9 @@ dependencies = [
 
 [[package]]
 name = "wit-parser"
-version = "0.252.0"
+version = "0.253.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4266bea110371c620ccf3201c5023676046bc4556e5c7cfb5d500bda5ebc162d"
+checksum = "4d997b8e5920fcbeec742b58e583325d6419a6aca617ae8075c406a61c65ba8a"
 dependencies = [
  "anyhow",
  "hashbrown 0.17.0",
@@ -6923,7 +6923,7 @@ dependencies = [
  "serde_derive",
  "serde_json",
  "unicode-ident",
- "wasmparser 0.252.0",
+ "wasmparser 0.253.0",
 ]
 
 [[package]]

compiler/rustc_abi/src/callconv.rs

@@ -89,7 +89,7 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
                 unreachable!("`homogeneous_aggregate` should not be called for scalable vectors")
             }
 
-            BackendRepr::ScalarPair(..) | BackendRepr::Memory { sized: true } => {
+            BackendRepr::ScalarPair { .. } | BackendRepr::Memory { sized: true } => {
                 // Helper for computing `homogeneous_aggregate`, allowing a custom
                 // starting offset (used below for handling variants).
                 let from_fields_at =

compiler/rustc_abi/src/layout.rs

@@ -476,7 +476,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             Err(AbiMismatch) | Ok(None) => BackendRepr::Memory { sized: true },
             Ok(Some((repr, _))) => match repr {
                 // Mismatched alignment (e.g. union is #[repr(packed)]): disable opt
-                BackendRepr::Scalar(_) | BackendRepr::ScalarPair(_, _)
+                BackendRepr::Scalar(_) | BackendRepr::ScalarPair { .. }
                     if repr.scalar_platform_align(dl).unwrap() != align =>
                 {
                     BackendRepr::Memory { sized: true }
@@ -489,7 +489,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 }
                 // the alignment tests passed and we can use this
                 BackendRepr::Scalar(..)
-                | BackendRepr::ScalarPair(..)
+                | BackendRepr::ScalarPair { .. }
                 | BackendRepr::SimdVector { .. }
                 | BackendRepr::SimdScalableVector { .. }
                 | BackendRepr::Memory { .. } => repr,
@@ -558,7 +558,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             };
             match &mut st.backend_repr {
                 BackendRepr::Scalar(scalar) => hide_niches(scalar),
-                BackendRepr::ScalarPair(a, b) => {
+                BackendRepr::ScalarPair { a, b, b_offset: _ } => {
                     hide_niches(a);
                     hide_niches(b);
                 }
@@ -701,13 +701,21 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                     // When the total alignment and size match, we can use the
                     // same ABI as the scalar variant with the reserved niche.
                     BackendRepr::Scalar(_) => BackendRepr::Scalar(niche_scalar),
-                    BackendRepr::ScalarPair(first, second) => {
+                    BackendRepr::ScalarPair { a: first, b: second, b_offset } => {
                         // Only the niche is guaranteed to be initialised,
                         // so use union layouts for the other primitive.
                         if niche_offset == Size::ZERO {
-                            BackendRepr::ScalarPair(niche_scalar, second.to_union())
+                            BackendRepr::ScalarPair {
+                                a: niche_scalar,
+                                b: second.to_union(),
+                                b_offset,
+                            }
                         } else {
-                            BackendRepr::ScalarPair(first.to_union(), niche_scalar)
+                            BackendRepr::ScalarPair {
+                                a: first.to_union(),
+                                b: niche_scalar,
+                                b_offset,
+                            }
                         }
                     }
                     _ => BackendRepr::Memory { sized: true },
@@ -1037,7 +1045,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         // If we pick a "clever" (by-value) ABI, we might have to adjust the ABI of the
         // variants to ensure they are consistent. This is because a downcast is
         // semantically a NOP, and thus should not affect layout.
-        if matches!(abi, BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..)) {
+        if matches!(abi, BackendRepr::Scalar(..) | BackendRepr::ScalarPair { .. }) {
             for variant in &mut layout_variants {
                 // We only do this for variants with fields; the others are not accessed anyway.
                 // Also do not overwrite any already existing "clever" ABIs.
@@ -1354,7 +1362,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                             }
                             // But scalar pairs are Rust-specific and get
                             // treated as aggregates by C ABIs anyway.
-                            BackendRepr::ScalarPair(..) => {
+                            BackendRepr::ScalarPair { .. } => {
                                 abi = field.backend_repr;
                             }
                             _ => {}

compiler/rustc_abi/src/layout/simple.rs

@@ -110,7 +110,7 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
                 offsets: [Size::ZERO, b_offset].into(),
                 in_memory_order: [FieldIdx::new(0), FieldIdx::new(1)].into(),
             },
-            backend_repr: BackendRepr::ScalarPair(a, b),
+            backend_repr: BackendRepr::ScalarPair { a, b, b_offset },
             largest_niche,
             uninhabited: false,
             align: AbiAlign::new(align),

compiler/rustc_abi/src/lib.rs

@@ -1796,14 +1796,18 @@ impl IntoDiagArg for NumScalableVectors {
 pub enum BackendRepr {
     Scalar(Scalar),
     /// The data contained in this type can be entirely represented by two scalars.
-    /// The two scalars are listed in *memory* order, so the first is at offset zero
-    /// and the second at a non-zero offset.
+    /// The two scalars are listed in *memory* order, so `a` is at offset zero
+    /// and `b` is at non-zero offset `b_offset`.
     /// These need not be `FieldIdx(0)` and `FieldIdx(1)`.
     ///
-    /// As of June 2026 the offset to the second scalar is the size of the first
-    /// scalar rounded up to the platform alignment of the second scalar.
+    /// As of June 2026 the `b_offset` is always the size of the `a`
+    /// scalar rounded up to the platform alignment of the `b` scalar.
     /// That may soon change, however; see MCP#1007.
-    ScalarPair(Scalar, Scalar),
+    ScalarPair {
+        a: Scalar,
+        b: Scalar,
+        b_offset: Size,
+    },
     SimdScalableVector {
         element: Scalar,
         count: u64,
@@ -1826,7 +1830,7 @@ impl BackendRepr {
     pub fn is_unsized(&self) -> bool {
         match *self {
             BackendRepr::Scalar(_)
-            | BackendRepr::ScalarPair(..)
+            | BackendRepr::ScalarPair { .. }
             // FIXME(rustc_scalable_vector): Scalable vectors are `Sized` while the
             // `sized_hierarchy` feature is not yet fully implemented. After `sized_hierarchy` is
             // fully implemented, scalable vectors will remain `Sized`, they just won't be
@@ -1875,7 +1879,7 @@ impl BackendRepr {
     pub fn scalar_platform_align<C: HasDataLayout>(&self, cx: &C) -> Option<Align> {
         match *self {
             BackendRepr::Scalar(s) => Some(s.default_align(cx).abi),
-            BackendRepr::ScalarPair(s1, s2) => {
+            BackendRepr::ScalarPair { a: s1, b: s2, b_offset: _ } => {
                 Some(s1.default_align(cx).max(s2.default_align(cx)).abi)
             }
             // The align of a Vector can vary in surprising ways
@@ -1893,8 +1897,7 @@ impl BackendRepr {
             // No padding in scalars.
             BackendRepr::Scalar(s) => Some(s.size(cx)),
             // May have some padding between the pair.
-            BackendRepr::ScalarPair(s1, s2) => {
-                let field2_offset = s1.size(cx).align_to(s2.default_align(cx).abi);
+            BackendRepr::ScalarPair { a: _, b: s2, b_offset: field2_offset } => {
                 let size = (field2_offset + s2.size(cx)).align_to(
                     self.scalar_platform_align(cx)
                         // We absolutely must have an answer here or everything is FUBAR.
@@ -1913,8 +1916,8 @@ impl BackendRepr {
     pub fn to_union(&self) -> Self {
         match *self {
             BackendRepr::Scalar(s) => BackendRepr::Scalar(s.to_union()),
-            BackendRepr::ScalarPair(s1, s2) => {
-                BackendRepr::ScalarPair(s1.to_union(), s2.to_union())
+            BackendRepr::ScalarPair { a: s1, b: s2, b_offset } => {
+                BackendRepr::ScalarPair { a: s1.to_union(), b: s2.to_union(), b_offset }
             }
             BackendRepr::SimdVector { element, count } => {
                 BackendRepr::SimdVector { element: element.to_union(), count }
@@ -1939,8 +1942,13 @@ impl BackendRepr {
                 BackendRepr::SimdVector { element: element_l, count: count_l },
                 BackendRepr::SimdVector { element: element_r, count: count_r },
             ) => element_l.primitive() == element_r.primitive() && count_l == count_r,
-            (BackendRepr::ScalarPair(l1, l2), BackendRepr::ScalarPair(r1, r2)) => {
-                l1.primitive() == r1.primitive() && l2.primitive() == r2.primitive()
+            (
+                BackendRepr::ScalarPair { a: l1, b: l2, b_offset: l_offset },
+                BackendRepr::ScalarPair { a: r1, b: r2, b_offset: r_offset },
+            ) => {
+                l1.primitive() == r1.primitive()
+                    && l2.primitive() == r2.primitive()
+                    && l_offset == r_offset
             }
             // Everything else must be strictly identical.
             _ => self == other,
@@ -2180,7 +2188,7 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
             BackendRepr::Scalar(_)
             | BackendRepr::SimdVector { .. }
             | BackendRepr::SimdScalableVector { .. } => false,
-            BackendRepr::ScalarPair(..) | BackendRepr::Memory { .. } => true,
+            BackendRepr::ScalarPair { .. } | BackendRepr::Memory { .. } => true,
         }
     }
 
@@ -2294,7 +2302,7 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
     pub fn is_zst(&self) -> bool {
         match self.backend_repr {
             BackendRepr::Scalar(_)
-            | BackendRepr::ScalarPair(..)
+            | BackendRepr::ScalarPair { .. }
             | BackendRepr::SimdScalableVector { .. }
             | BackendRepr::SimdVector { .. } => false,
             BackendRepr::Memory { sized } => sized && self.size.bytes() == 0,