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Allow spreading records in type constructors for const values #5061

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5d39a71
Implement record spreading in const values
abs0luty Oct 31, 2025
2864ed1
Merge branch 'main' into spreading-in-const-records
abs0luty Nov 10, 2025
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8 changes: 8 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -51,6 +51,14 @@
containing scientific notation or trailing zeros (i.e. `100` and `1e2`).
([ptdewey](https://github.com/ptdewey))

- Record update syntax now works with spreading records in type constructors
for const values:
```gleam
const a = Foo(1, 2)
const b = Foo(..a, 3)
```
([Adi Salimgereyev](https://github.com/abs0luty))

### Build tool

- The help text displayed by `gleam dev --help`, `gleam test --help`, and
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22 changes: 17 additions & 5 deletions compiler-core/src/ast/constant.rs
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Expand Up @@ -40,6 +40,7 @@ pub enum Constant<T, RecordTag> {
module: Option<(EcoString, SrcSpan)>,
name: EcoString,
arguments: Vec<CallArg<Self>>,
spread: Option<Box<Self>>,
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@lpil lpil Nov 10, 2025

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For non-constant expressions record updates have their own AST node, is there a reason not to do that here? It would mean that the overrides have to be labelled, which is nice to enforce.

tag: RecordTag,
type_: T,
field_map: Option<FieldMap>,
Expand Down Expand Up @@ -104,9 +105,12 @@ impl TypedConstant {
.iter()
.find_map(|element| element.find_node(byte_index))
.unwrap_or(Located::Constant(self)),
Constant::Record { arguments, .. } => arguments
Constant::Record {
arguments, spread, ..
} => arguments
.iter()
.find_map(|argument| argument.find_node(byte_index))
.or_else(|| spread.as_ref().and_then(|s| s.find_node(byte_index)))
.unwrap_or(Located::Constant(self)),
Constant::BitArray { segments, .. } => segments
.iter()
Expand Down Expand Up @@ -156,10 +160,18 @@ impl TypedConstant {
.map(|element| element.referenced_variables())
.fold(im::hashset![], im::HashSet::union),

Constant::Record { arguments, .. } => arguments
.iter()
.map(|argument| argument.value.referenced_variables())
.fold(im::hashset![], im::HashSet::union),
Constant::Record {
arguments, spread, ..
} => {
let arg_vars = arguments
.iter()
.map(|argument| argument.value.referenced_variables())
.fold(im::hashset![], im::HashSet::union);
match spread {
Some(spread) => arg_vars.union(spread.referenced_variables()),
None => arg_vars,
}
}

Constant::BitArray { segments, .. } => segments
.iter()
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8 changes: 7 additions & 1 deletion compiler-core/src/ast_folder.rs
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Expand Up @@ -972,11 +972,12 @@ pub trait UntypedConstantFolder {
module,
name,
arguments,
spread,
tag: (),
type_: (),
field_map: _,
record_constructor: _,
} => self.fold_constant_record(location, module, name, arguments),
} => self.fold_constant_record(location, module, name, arguments, spread),

Constant::BitArray { location, segments } => {
self.fold_constant_bit_array(location, segments)
Expand Down Expand Up @@ -1059,12 +1060,14 @@ pub trait UntypedConstantFolder {
module: Option<(EcoString, SrcSpan)>,
name: EcoString,
arguments: Vec<CallArg<UntypedConstant>>,
spread: Option<Box<UntypedConstant>>,
) -> UntypedConstant {
Constant::Record {
location,
module,
name,
arguments,
spread,
tag: (),
type_: (),
field_map: None,
Expand Down Expand Up @@ -1146,6 +1149,7 @@ pub trait UntypedConstantFolder {
module,
name,
arguments,
spread,
tag,
type_,
field_map,
Expand All @@ -1158,11 +1162,13 @@ pub trait UntypedConstantFolder {
argument
})
.collect();
let spread = spread.map(|s| Box::new(self.fold_constant(*s)));
Constant::Record {
location,
module,
name,
arguments,
spread,
tag,
type_,
field_map,
Expand Down
5 changes: 3 additions & 2 deletions compiler-core/src/erlang.rs
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Expand Up @@ -1542,11 +1542,12 @@ fn const_inline<'a>(literal: &'a TypedConstant, env: &mut Env<'a>) -> Document<'
},

Constant::Record { tag, arguments, .. } => {
let arguments = arguments
// Spreads are fully expanded during type checking, so we just handle arguments
let arguments_doc = arguments
.iter()
.map(|argument| const_inline(&argument.value, env));
let tag = atom_string(to_snake_case(tag));
tuple(std::iter::once(tag).chain(arguments))
tuple(std::iter::once(tag).chain(arguments_doc))
}

Constant::Var {
Expand Down
2 changes: 2 additions & 0 deletions compiler-core/src/javascript/expression.rs
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Expand Up @@ -1839,6 +1839,7 @@ impl<'module, 'a> Generator<'module, 'a> {
return record_constructor(type_.clone(), None, name, arity, self.tracker);
}

// Spreads are fully expanded during type checking, so we just handle arguments
let field_values = arguments
.iter()
.map(|argument| self.constant_expression(context, &argument.value))
Expand Down Expand Up @@ -2253,6 +2254,7 @@ impl<'module, 'a> Generator<'module, 'a> {
return record_constructor(type_.clone(), None, name, arity, self.tracker);
}

// Spreads are fully expanded during type checking, so we just handle arguments
let field_values = arguments
.iter()
.map(|argument| self.guard_constant_expression(&argument.value))
Expand Down
1 change: 1 addition & 0 deletions compiler-core/src/metadata/module_decoder.rs
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Expand Up @@ -437,6 +437,7 @@ impl ModuleDecoder {
module: Default::default(),
name: Default::default(),
arguments,
spread: None,
tag,
type_,
field_map: None,
Expand Down
1 change: 1 addition & 0 deletions compiler-core/src/metadata/tests.rs
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Expand Up @@ -1164,6 +1164,7 @@ fn constant_record() {
},
},
],
spread: None,
tag: "thetag".into(),
type_: type_::int(),
field_map: None,
Expand Down
38 changes: 35 additions & 3 deletions compiler-core/src/parse.rs
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Expand Up @@ -3310,23 +3310,54 @@ where
) -> Result<Option<UntypedConstant>, ParseError> {
match self.maybe_one(&Token::LeftParen) {
Some((par_s, _)) => {
let arguments =
Parser::series_of(self, &Parser::parse_const_record_arg, Some(&Token::Comma))?;
// Check for spread syntax: Record(..base, ...)
let spread = match self.maybe_one(&Token::DotDot) {
Some(_) => {
// Parse the spread target constant
let spread_value = self.parse_const_value()?;
match spread_value {
Some(value) => Some(Box::new(value)),
None => {
return parse_error(
ParseErrorType::UnexpectedEof,
SrcSpan::new(par_s, par_s + 2),
);
}
}
}
None => None,
};

// Parse remaining arguments after the spread (if any)
let mut arguments = vec![];
if (spread.is_some() && self.maybe_one(&Token::Comma).is_some()) || spread.is_none()
{
arguments = Parser::series_of(
self,
&Parser::parse_const_record_arg,
Some(&Token::Comma),
)?;
}

let (_, par_e) = self.expect_one_following_series(
&Token::RightParen,
"a constant record argument",
)?;
if arguments.is_empty() {

// Validate that we have either arguments or a spread
if arguments.is_empty() && spread.is_none() {
return parse_error(
ParseErrorType::ConstantRecordConstructorNoArguments,
SrcSpan::new(par_s, par_e),
);
}

Ok(Some(Constant::Record {
location: SrcSpan { start, end: par_e },
module,
name,
arguments,
spread,
tag: (),
type_: (),
field_map: None,
Expand All @@ -3338,6 +3369,7 @@ where
module,
name,
arguments: vec![],
spread: None,
tag: (),
type_: (),
field_map: None,
Expand Down
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