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Add map support #1562

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107 changes: 101 additions & 6 deletions crates/c/src/lib.rs
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@alexcrichton alexcrichton Mar 16, 2026

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Similar to other languages, I don't think this should be added without tests. Unlike other languages, though, I can review this, so mind adding some tests using the C bits?

Original file line number Diff line number Diff line change
Expand Up @@ -1088,7 +1088,7 @@ fn is_prim_type_id(resolve: &Resolve, id: TypeId) -> bool {
| TypeDefKind::Stream(_)
| TypeDefKind::Unknown => false,
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(key, value) => is_prim_type(resolve, key) && is_prim_type(resolve, value),
}
}

Expand Down Expand Up @@ -1174,7 +1174,12 @@ pub fn push_ty_name(resolve: &Resolve, ty: &Type, src: &mut String) {
}
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(key, value) => {
src.push_str("map_");
push_ty_name(resolve, key, src);
src.push_str("_");
push_ty_name(resolve, value, src);
}
}
}
}
Expand Down Expand Up @@ -1383,12 +1388,12 @@ impl Return {
TypeDefKind::Tuple(_)
| TypeDefKind::Record(_)
| TypeDefKind::List(_)
| TypeDefKind::Map(_, _)
| TypeDefKind::Variant(_) => {}

TypeDefKind::Resource => todo!("return_single for resource"),
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
}

self.retptrs.push(*orig_ty);
Expand Down Expand Up @@ -1735,6 +1740,23 @@ void __wasm_export_{ns}_{snake}_dtor({ns}_{snake}_t* arg) {{
self.finish_typedef_struct(id);
}

fn type_map(&mut self, id: TypeId, _name: &str, key: &Type, value: &Type, docs: &Docs) {
self.src.h_defs("\n");
self.docs(docs, SourceType::HDefs);
let map_ty = self.r#gen.type_name(&Type::Id(id));
let entry_ty = format!("{map_ty}_entry_t");
uwriteln!(self.src.h_defs, "typedef struct {entry_ty} {{");
self.print_ty(SourceType::HDefs, key);
self.src.h_defs(" key;\n");
self.print_ty(SourceType::HDefs, value);
self.src.h_defs(" value;\n");
uwriteln!(self.src.h_defs, "}} {entry_ty};");
self.start_typedef_struct(id);
uwriteln!(self.src.h_defs, "{entry_ty} *ptr;");
self.src.h_defs("size_t len;\n");
self.finish_typedef_struct(id);
}

fn type_fixed_length_list(
&mut self,
_id: TypeId,
Expand Down Expand Up @@ -1844,6 +1866,24 @@ impl<'a> wit_bindgen_core::AnonymousTypeGenerator<'a> for InterfaceGenerator<'a>
self.print_typedef_target(id);
}

fn anonymous_type_map(&mut self, id: TypeId, key: &Type, value: &Type, _docs: &Docs) {
let map_ty = self.r#gen.type_name(&Type::Id(id));
let entry_ty = format!("{map_ty}_entry_t");
uwriteln!(self.src.h_defs, "\ntypedef struct {entry_ty} {{");
self.print_ty(SourceType::HDefs, key);
self.src.h_defs(" key;\n");
self.print_ty(SourceType::HDefs, value);
self.src.h_defs(" value;\n");
uwriteln!(self.src.h_defs, "}} {entry_ty};");
self.src.h_defs("\ntypedef ");
self.src.h_defs("struct {\n");
uwriteln!(self.src.h_defs, "{entry_ty} *ptr;");
self.src.h_defs("size_t len;\n");
self.src.h_defs("}");
self.src.h_defs(" ");
self.print_typedef_target(id);
}

fn anonymous_type_future(&mut self, id: TypeId, _ty: &Option<Type>, _docs: &Docs) {
self.src.h_defs("\ntypedef uint32_t ");
self.print_typedef_target(id);
Expand Down Expand Up @@ -2005,6 +2045,21 @@ impl InterfaceGenerator<'_> {
uwriteln!(self.src.c_helpers, "}}");
}

TypeDefKind::Map(key, value) => {
self.src.c_helpers("size_t map_len = ptr->len;\n");
uwriteln!(self.src.c_helpers, "if (map_len > 0) {{");
let map_ty = self.r#gen.type_name(&Type::Id(id));
let entry_ty = format!("{map_ty}_entry_t");
uwriteln!(self.src.c_helpers, "{entry_ty} *map_ptr = ptr->ptr;");
self.src
.c_helpers("for (size_t i = 0; i < map_len; i++) {\n");
self.free(key, "&map_ptr[i].key");
self.free(value, "&map_ptr[i].value");
self.src.c_helpers("}\n");
uwriteln!(self.src.c_helpers, "free(map_ptr);");
uwriteln!(self.src.c_helpers, "}}");
}

TypeDefKind::Variant(v) => {
self.src.c_helpers("switch ((int32_t) ptr->tag) {\n");
for (i, case) in v.cases.iter().enumerate() {
Expand Down Expand Up @@ -2045,7 +2100,6 @@ impl InterfaceGenerator<'_> {
}
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
}
if c_helpers_body_start == self.src.c_helpers.len() {
self.src.c_helpers.as_mut_string().truncate(c_helpers_start);
Expand Down Expand Up @@ -2739,7 +2793,9 @@ void {name}_return({return_ty}) {{

TypeDefKind::Unknown => false,
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(key, value) => {
self.contains_droppable_borrow(key) || self.contains_droppable_borrow(value)
}
}
} else {
false
Expand Down Expand Up @@ -3609,6 +3665,11 @@ impl Bindgen for FunctionBindgen<'_, '_> {
results.push(format!("(uint8_t *) ({}).ptr", operands[0]));
results.push(format!("({}).len", operands[0]));
}
Instruction::MapLower { .. } => {
let _body = self.blocks.pop().unwrap();
results.push(format!("(uint8_t *) ({}).ptr", operands[0]));
results.push(format!("({}).len", operands[0]));
}

Instruction::ListLift { element, ty, .. } => {
self.assert_no_droppable_borrows("list", &Type::Id(*ty));
Expand All @@ -3621,7 +3682,19 @@ impl Bindgen for FunctionBindgen<'_, '_> {
list_name, elem_name, operands[0], operands[1]
));
}
Instruction::MapLift { ty, .. } => {
let _body = self.blocks.pop().unwrap();
self.assert_no_droppable_borrows("map", &Type::Id(*ty));
let map_name = self.r#gen.r#gen.type_name(&Type::Id(*ty));
let entry_name = format!("{map_name}_entry_t");
results.push(format!(
"({}) {{ ({}*)({}), ({}) }}",
map_name, entry_name, operands[0], operands[1]
));
}
Instruction::IterElem { .. } => results.push("e".to_string()),
Instruction::IterMapKey { .. } => results.push("map_key".to_string()),
Instruction::IterMapValue { .. } => results.push("map_value".to_string()),
Instruction::IterBasePointer => results.push("base".to_string()),

Instruction::CallWasm { sig, .. } => {
Expand Down Expand Up @@ -3956,6 +4029,28 @@ impl Bindgen for FunctionBindgen<'_, '_> {
uwriteln!(self.src, "free({ptr});");
uwriteln!(self.src, "}}");
}
Instruction::GuestDeallocateMap { key, value } => {
let (body, results) = self.blocks.pop().unwrap();
assert!(results.is_empty());
let len = self.locals.tmp("len");
uwriteln!(self.src, "size_t {len} = {};", operands[1]);
uwriteln!(self.src, "if ({len} > 0) {{");
let ptr = self.locals.tmp("ptr");
uwriteln!(self.src, "uint8_t *{ptr} = {};", operands[0]);
let i = self.locals.tmp("i");
uwriteln!(self.src, "for (size_t {i} = 0; {i} < {len}; {i}++) {{");
let size = self.r#gen.r#gen.sizes.record([*key, *value]).size;
uwriteln!(
self.src,
"uint8_t *base = {ptr} + {i} * {};",
size.format(POINTER_SIZE_EXPRESSION)
);
uwriteln!(self.src, "(void) base;");
uwrite!(self.src, "{body}");
uwriteln!(self.src, "}}");
uwriteln!(self.src, "free({ptr});");
uwriteln!(self.src, "}}");
}

Instruction::Flush { amt } => {
results.extend(operands.iter().take(*amt).cloned());
Expand Down Expand Up @@ -4109,7 +4204,7 @@ pub fn is_arg_by_pointer(resolve: &Resolve, ty: &Type) -> bool {
TypeDefKind::Resource => todo!("is_arg_by_pointer for resource"),
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(..) => true,
},
Type::String => true,
_ => false,
Expand Down
103 changes: 96 additions & 7 deletions crates/core/src/abi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -310,6 +310,28 @@ def_instruction! {
ty: TypeId,
} : [2] => [1],

/// Lowers a map into a canonical pointer/length pair.
///
/// This operation pops a map value from the stack and pushes pointer
/// and length. A block is popped from the block stack to lower one
/// key/value entry into linear memory.
MapLower {
key: &'a Type,
value: &'a Type,
realloc: Option<&'a str>,
} : [1] => [2],

/// Lifts a canonical pointer/length pair into a map.
///
/// This operation consumes pointer and length from the stack. A block
/// is popped from the block stack and must produce key/value for one
/// map entry.
MapLift {
key: &'a Type,
value: &'a Type,
ty: TypeId,
} : [2] => [1],

/// Pops all fields for a fixed list off the stack and then composes them
/// into an array.
FixedLengthListLift {
Expand Down Expand Up @@ -349,6 +371,14 @@ def_instruction! {
/// This is only used inside of blocks related to lowering lists.
IterElem { element: &'a Type } : [0] => [1],

/// Pushes an operand onto the stack representing the current map key
/// for each map iteration.
IterMapKey { key: &'a Type } : [0] => [1],

/// Pushes an operand onto the stack representing the current map value
/// for each map iteration.
IterMapValue { value: &'a Type } : [0] => [1],

/// Pushes an operand onto the stack representing the base pointer of
/// the next element in a list.
///
Expand Down Expand Up @@ -581,6 +611,17 @@ def_instruction! {
element: &'a Type,
} : [2] => [0],

/// Used exclusively for guest-code generation this indicates that a
/// map is being deallocated. The ptr/length are on the stack and are
/// popped off and used to deallocate the map entry buffer.
///
/// This variant also pops a block off the block stack to be used as
/// the body of the deallocation loop over map entries.
GuestDeallocateMap {
key: &'a Type,
value: &'a Type,
} : [2] => [0],

/// Used exclusively for guest-code generation this indicates that
/// a variant is being deallocated. The integer discriminant is popped
/// off the stack as well as `blocks` number of blocks popped from the
Expand Down Expand Up @@ -875,7 +916,7 @@ fn needs_deallocate(resolve: &Resolve, ty: &Type, what: Deallocate) -> bool {
TypeDefKind::Future(_) | TypeDefKind::Stream(_) => what.handles(),
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(t, _) => needs_deallocate(resolve, t, what),
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(_, _) => true,
},

Type::Bool
Expand Down Expand Up @@ -1618,7 +1659,25 @@ impl<'a, B: Bindgen> Generator<'a, B> {
self.lower(ty);
}
}
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(key, value) => {
let realloc = self.list_realloc();
let value_offset = self.bindgen.sizes().field_offsets([key, value])[1].0;
self.push_block();
self.emit(&IterMapKey { key });
self.emit(&IterBasePointer);
let key_addr = self.stack.pop().unwrap();
self.write_to_memory(key, key_addr, Default::default());
self.emit(&IterMapValue { value });
self.emit(&IterBasePointer);
let value_addr = self.stack.pop().unwrap();
self.write_to_memory(value, value_addr, value_offset);
self.finish_block(0);
self.emit(&MapLower {
key,
value,
realloc,
});
}
},
}
}
Expand Down Expand Up @@ -1819,7 +1878,16 @@ impl<'a, B: Bindgen> Generator<'a, B> {
id,
});
}
TypeDefKind::Map(..) => todo!(),
TypeDefKind::Map(key, value) => {
let value_offset = self.bindgen.sizes().field_offsets([key, value])[1].0;
self.push_block();
self.emit(&IterBasePointer);
let entry_addr = self.stack.pop().unwrap();
self.read_from_memory(key, entry_addr.clone(), Default::default());
self.read_from_memory(value, entry_addr, value_offset);
self.finish_block(2);
self.emit(&MapLift { key, value, ty: id });
}
},
}
}
Expand Down Expand Up @@ -1907,6 +1975,7 @@ impl<'a, B: Bindgen> Generator<'a, B> {
Type::Id(id) => match &self.resolve.types[id].kind {
TypeDefKind::Type(t) => self.write_to_memory(t, addr, offset),
TypeDefKind::List(_) => self.write_list_to_memory(ty, addr, offset),
TypeDefKind::Map(_, _) => self.write_list_to_memory(ty, addr, offset),
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@alexcrichton alexcrichton Mar 16, 2026

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Similar to below, can this have a comment for why write_list_to_memory works?


TypeDefKind::Future(_) | TypeDefKind::Stream(_) | TypeDefKind::Handle(_) => {
self.lower_and_emit(ty, addr, &I32Store { offset })
Expand Down Expand Up @@ -2016,7 +2085,6 @@ impl<'a, B: Bindgen> Generator<'a, B> {
id,
});
}
TypeDefKind::Map(..) => todo!(),
},
}
}
Expand Down Expand Up @@ -2115,6 +2183,7 @@ impl<'a, B: Bindgen> Generator<'a, B> {
TypeDefKind::Type(t) => self.read_from_memory(t, addr, offset),

TypeDefKind::List(_) => self.read_list_from_memory(ty, addr, offset),
TypeDefKind::Map(_, _) => self.read_list_from_memory(ty, addr, offset),
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@alexcrichton alexcrichton Mar 16, 2026

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Can this have a comment for why read_list_from_memory works?


TypeDefKind::Future(_) | TypeDefKind::Stream(_) | TypeDefKind::Handle(_) => {
self.emit_and_lift(ty, addr, &I32Load { offset })
Expand Down Expand Up @@ -2216,7 +2285,6 @@ impl<'a, B: Bindgen> Generator<'a, B> {
id,
});
}
TypeDefKind::Map(..) => todo!(),
},
}
}
Expand Down Expand Up @@ -2339,6 +2407,18 @@ impl<'a, B: Bindgen> Generator<'a, B> {
self.emit(&Instruction::GuestDeallocateList { element });
}

TypeDefKind::Map(key, value) => {
let value_offset = self.bindgen.sizes().field_offsets([key, value])[1].0;
self.push_block();
self.emit(&IterBasePointer);
let entry_addr = self.stack.pop().unwrap();
self.deallocate_indirect(key, entry_addr.clone(), Default::default(), what);
self.deallocate_indirect(value, entry_addr, value_offset, what);
self.finish_block(0);

self.emit(&Instruction::GuestDeallocateMap { key, value });
}

TypeDefKind::Handle(Handle::Own(_))
| TypeDefKind::Future(_)
| TypeDefKind::Stream(_)
Expand Down Expand Up @@ -2405,7 +2485,6 @@ impl<'a, B: Bindgen> Generator<'a, B> {
TypeDefKind::Unknown => unreachable!(),

TypeDefKind::FixedLengthList(..) => todo!(),
TypeDefKind::Map(..) => todo!(),
},
}
}
Expand Down Expand Up @@ -2464,6 +2543,17 @@ impl<'a, B: Bindgen> Generator<'a, B> {
self.deallocate(ty, what);
}

TypeDefKind::Map(_, _) => {
self.stack.push(addr.clone());
self.emit(&Instruction::PointerLoad { offset });
self.stack.push(addr);
self.emit(&Instruction::LengthLoad {
offset: offset + self.bindgen.sizes().align(ty).into(),
});

self.deallocate(ty, what);
}

TypeDefKind::Handle(Handle::Own(_))
| TypeDefKind::Future(_)
| TypeDefKind::Stream(_)
Expand Down Expand Up @@ -2527,7 +2617,6 @@ impl<'a, B: Bindgen> Generator<'a, B> {
TypeDefKind::Stream(_) => unreachable!(),
TypeDefKind::Unknown => unreachable!(),
TypeDefKind::FixedLengthList(_, _) => {}
TypeDefKind::Map(..) => todo!(),
},
}
}
Expand Down
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