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alexcrichton merged 2 commits into from
May 22, 2026
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refactor: Remove inline wasm ABI pointer shifts #1616

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ef1cbff
fix: remove inline wasm ABI pointer shifts
peter-jerry-ye May 22, 2026
e3e3193
docs: note MoonBit ABI layout change
peter-jerry-ye May 22, 2026
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13 changes: 13 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -410,6 +410,19 @@ This can be useful having one project that exports multiple worlds.
When using `wit-bindgen moonbit`, you may use `--derive-show` or `--derive-eq` to derive `Show` or `Eq` traits for all types.
You may also use `--derive-error`, which will make types containing `Error` as error types in MoonBit.

#### MoonBit ABI compatibility

The MoonBit generator emits inline wasm helpers for strings, bytes, and arrays.
MoonBit changed the ABI layout for these values so the data pointer no longer
needs the old 8-byte offset. This is a breaking change for generated MoonBit
bindings that use inline wasm, but it is not something the MoonBit compiler can
detect at the type level.

Regenerate MoonBit bindings with a `wit-bindgen` version that matches the
MoonBit toolchain ABI layout. If old generated bindings or an older MoonBit
toolchain are mixed with new bindings, components may still compile but fail at
runtime with corrupted strings/bytes or traps.

You will find the files to be modified with the name `**/stub.mbt`.
To avoid touching the files during regeneration (including `moon.pkg.json` or `moon.mod.json`) you may use `--ignore-stub`.

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68 changes: 34 additions & 34 deletions crates/moonbit/src/ffi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -98,101 +98,101 @@ pub(crate) const STR2PTR: &str = r#"
///|
#owned(str)
extern "wasm" fn mbt_ffi_str2ptr(str : String) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const PTR2STR: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2str(ptr : Int, len : Int) -> String =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array16
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const BYTES2PTR: &str = r#"
///|
#owned(bytes)
extern "wasm" fn mbt_ffi_bytes2ptr(bytes : FixedArray[Byte]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const PTR2BYTES: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2bytes(ptr : Int, len : Int) -> FixedArray[Byte] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array8
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const UINT_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_uint_array2ptr(array : FixedArray[UInt]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const UINT64_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_uint64_array2ptr(array : FixedArray[UInt64]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const INT_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_int_array2ptr(array : FixedArray[Int]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const INT64_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_int64_array2ptr(array : FixedArray[Int64]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const FLOAT_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_float_array2ptr(array : FixedArray[Float]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const DOUBLE_ARRAY2PTR: &str = r#"
///|
#owned(array)
extern "wasm" fn mbt_ffi_double_array2ptr(array : FixedArray[Double]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)
"#;

pub(crate) const PTR2UINT_ARRAY: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2uint_array(ptr : Int, len : Int) -> FixedArray[UInt] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const PTR2INT_ARRAY: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2int_array(ptr : Int, len : Int) -> FixedArray[Int] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const PTR2FLOAT_ARRAY: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2float_array(ptr : Int, len : Int) -> FixedArray[Float] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const PTR2UINT64_ARRAY: &str = r#"
Expand All @@ -201,19 +201,19 @@ extern "wasm" fn mbt_ffi_ptr2uint64_array(
ptr : Int,
len : Int,
) -> FixedArray[UInt64] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const PTR2INT64_ARRAY: &str = r#"
///|
extern "wasm" fn mbt_ffi_ptr2int64_array(ptr : Int, len : Int) -> FixedArray[Int64] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const PTR2DOUBLE_ARRAY: &str = r#"
Expand All @@ -222,10 +222,10 @@ extern "wasm" fn mbt_ffi_ptr2double_array(
ptr : Int,
len : Int,
) -> FixedArray[Double] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)
"#;

pub(crate) const MALLOC: &str = r#"
Expand All @@ -234,13 +234,13 @@ extern "wasm" fn mbt_ffi_malloc(size : Int) -> Int =
#|(func (param i32) (result i32) (local i32)
#| local.get 0 i32.const 4 i32.add call $moonbit.gc.malloc
#| local.tee 1 i32.const 0 call $moonbit.init_array8
#| local.get 1 i32.const 8 i32.add)
#| local.get 1)
"#;

pub(crate) const FREE: &str = r#"
///|
extern "wasm" fn mbt_ffi_free(position : Int) =
#|(func (param i32) local.get 0 i32.const 8 i32.sub call $moonbit.decref)
#|(func (param i32) local.get 0 call $moonbit.decref)
"#;

pub(crate) const CABI_REALLOC: &str = r#"
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68 changes: 34 additions & 34 deletions crates/moonbit/src/ffi/ffi.mbt
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Expand Up @@ -77,11 +77,11 @@ pub extern "wasm" fn malloc(size : Int) -> Int =
#|(func (param i32) (result i32) (local i32)
#| local.get 0 i32.const 4 i32.add call $moonbit.gc.malloc
#| local.tee 1 i32.const 0 call $moonbit.init_array8
#| local.get 1 i32.const 8 i32.add)
#| local.get 1)

///|
pub extern "wasm" fn free(position : Int) =
#|(func (param i32) local.get 0 i32.const 8 i32.sub call $moonbit.decref)
#|(func (param i32) local.get 0 call $moonbit.decref)

///|
extern "wasm" fn copy(dest : Int, src : Int, len : Int) =
Expand All @@ -90,104 +90,104 @@ extern "wasm" fn copy(dest : Int, src : Int, len : Int) =
///|
#owned(str)
pub extern "wasm" fn str2ptr(str : String) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
pub extern "wasm" fn ptr2str(ptr : Int, len : Int) -> String =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array16
#| local.get 2)
#| local.get 0)

///|
#owned(bytes)
pub extern "wasm" fn bytes2ptr(bytes : FixedArray[Byte]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
pub extern "wasm" fn ptr2bytes(ptr : Int, len : Int) -> FixedArray[Byte] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array8
#| local.get 2)
#| local.get 0)

///|
#owned(array)
pub extern "wasm" fn uint_array2ptr(array : FixedArray[UInt]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
#owned(array)
pub extern "wasm" fn uint64_array2ptr(array : FixedArray[UInt64]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
#owned(array)
pub extern "wasm" fn int_array2ptr(array : FixedArray[Int]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
#owned(array)
pub extern "wasm" fn int64_array2ptr(array : FixedArray[Int64]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
#owned(array)
pub extern "wasm" fn float_array2ptr(array : FixedArray[Float]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
#owned(array)
pub extern "wasm" fn double_array2ptr(array : FixedArray[Double]) -> Int =
#|(func (param i32) (result i32) local.get 0 i32.const 8 i32.add)
#|(func (param i32) (result i32) local.get 0)

///|
pub extern "wasm" fn ptr2uint_array(ptr : Int, len : Int) -> FixedArray[UInt] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)

///|
pub extern "wasm" fn ptr2int_array(ptr : Int, len : Int) -> FixedArray[Int] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)

///|
pub extern "wasm" fn ptr2float_array(ptr : Int, len : Int) -> FixedArray[Float] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array32
#| local.get 2)
#| local.get 0)

///|
pub extern "wasm" fn ptr2uint64_array(
ptr : Int,
len : Int,
) -> FixedArray[UInt64] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)

///|
pub extern "wasm" fn ptr2int64_array(ptr : Int, len : Int) -> FixedArray[Int64] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)

///|
pub extern "wasm" fn ptr2double_array(
ptr : Int,
len : Int,
) -> FixedArray[Double] =
#|(func (param i32) (param i32) (result i32) (local i32)
#| local.get 0 i32.const 8 i32.sub local.tee 2
#|(func (param i32) (param i32) (result i32)
#| local.get 0
#| local.get 1 call $moonbit.init_array64
#| local.get 2)
#| local.get 0)

///|
pub fn cabi_realloc(
Expand Down
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