Destructuring assign (#703)

src/eval/func.rs

@@ -445,7 +445,9 @@ impl<'a> CapturesVisitor<'a> {
                     match param {
                         ast::Param::Pos(ident) => self.bind(ident),
                         ast::Param::Named(named) => self.bind(named.name()),
-                        ast::Param::Sink(Some(ident)) => self.bind(ident),
+                        ast::Param::Sink(spread) => {
+                            self.bind(spread.name().unwrap_or_default())
+                        }
                         _ => {}
                     }
                 }

src/eval/mod.rs

@@ -456,6 +456,7 @@ impl Eval for ast::Expr {
             Self::Unary(v) => v.eval(vm),
             Self::Binary(v) => v.eval(vm),
             Self::Let(v) => v.eval(vm),
+            Self::DestructAssign(v) => v.eval(vm),
             Self::Set(_) => bail!(forbidden("set")),
             Self::Show(_) => bail!(forbidden("show")),
             Self::Conditional(v) => v.eval(vm),
@@ -1212,8 +1213,8 @@ impl Eval for ast::Closure {
                 ast::Param::Named(named) => {
                     params.push(Param::Named(named.name(), named.expr().eval(vm)?));
                 }
-                ast::Param::Sink(name) => params.push(Param::Sink(name)),
-                ast::Param::Placeholder => params.push(Param::Placeholder),
+                ast::Param::Sink(spread) => params.push(Param::Sink(spread.name())),
+                ast::Param::Placeholder(_) => params.push(Param::Placeholder),
             }
         }
 
@@ -1231,97 +1232,141 @@ impl Eval for ast::Closure {
 }
 
 impl ast::Pattern {
-    // Destruct the given value into the pattern.
-    #[tracing::instrument(skip_all)]
-    pub fn define(&self, vm: &mut Vm, value: Value) -> SourceResult<Value> {
-        match self {
-            ast::Pattern::Ident(ident) => {
-                vm.define(ident.clone(), value);
-                Ok(Value::None)
-            }
-            ast::Pattern::Placeholder => Ok(Value::None),
-            ast::Pattern::Destructuring(destruct) => {
-                match value {
-                    Value::Array(value) => {
-                        let mut i = 0;
-                        for p in destruct.bindings() {
-                            match p {
-                                ast::DestructuringKind::Ident(ident) => {
-                                    let Ok(v) = value.at(i) else {
-                                        bail!(ident.span(), "not enough elements to destructure");
-                                    };
-                                    vm.define(ident.clone(), v.clone());
-                                    i += 1;
-                                }
-                                ast::DestructuringKind::Sink(ident) => {
-                                    (1 + value.len() as usize).checked_sub(destruct.bindings().count()).and_then(|sink_size| {
-                                        let Ok(sink) = value.slice(i, Some(i + sink_size as i64)) else {
-                                            return None;
-                                        };
-                                        if let Some(ident) = ident {
-                                            vm.define(ident, sink);
-                                        }
-                                        i += sink_size as i64;
-                                        Some(())
-                                    }).ok_or("not enough elements to destructure").at(self.span())?;
-                                }
-                                ast::DestructuringKind::Named(key, _) => {
-                                    bail!(
-                                        key.span(),
-                                        "cannot destructure named elements from an array"
-                                    )
-                                }
-                                ast::DestructuringKind::Placeholder => i += 1,
-                            }
-                        }
-                        if i < value.len() {
-                            bail!(self.span(), "too many elements to destructure");
-                        }
-                    }
-                    Value::Dict(value) => {
-                        let mut sink = None;
-                        let mut used = HashSet::new();
-                        for p in destruct.bindings() {
-                            match p {
-                                ast::DestructuringKind::Ident(ident) => {
-                                    let Ok(v) = value.at(&ident) else {
-                                        bail!(ident.span(), "destructuring key not found in dictionary");
-                                    };
-                                    vm.define(ident.clone(), v.clone());
-                                    used.insert(ident.clone().take());
-                                }
-                                ast::DestructuringKind::Sink(ident) => {
-                                    sink = ident.clone()
-                                }
-                                ast::DestructuringKind::Named(key, ident) => {
-                                    let Ok(v) = value.at(&key) else {
-                                        bail!(ident.span(), "destructuring key not found in dictionary");
-                                    };
-                                    vm.define(ident.clone(), v.clone());
-                                    used.insert(key.clone().take());
-                                }
-                                ast::DestructuringKind::Placeholder => {}
-                            }
-                        }
+    fn destruct_array<T>(
+        &self,
+        vm: &mut Vm,
+        value: Array,
+        f: T,
+        destruct: &ast::Destructuring,
+    ) -> SourceResult<Value>
+    where
+        T: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<Value>,
+    {
+        let mut i = 0;
+        for p in destruct.bindings() {
+            match p {
+                ast::DestructuringKind::Normal(expr) => {
+                    let Ok(v) = value.at(i) else {
+                        bail!(expr.span(), "not enough elements to destructure");
+                    };
+                    f(vm, expr, v.clone())?;
+                    i += 1;
+                }
+                ast::DestructuringKind::Sink(spread) => {
+                    let sink_size = (1 + value.len() as usize)
+                        .checked_sub(destruct.bindings().count());
+                    let sink =
+                        sink_size.and_then(|s| value.slice(i, Some(i + s as i64)).ok());
 
-                        if let Some(ident) = sink {
-                            let mut sink = Dict::new();
-                            for (key, value) in value {
-                                if !used.contains(key.as_str()) {
-                                    sink.insert(key, value);
-                                }
-                            }
-                            vm.define(ident, Value::Dict(sink));
+                    if let (Some(sink_size), Some(sink)) = (sink_size, sink) {
+                        if let Some(expr) = spread.expr() {
+                            f(vm, expr, Value::Array(sink.clone()))?;
                         }
-                    }
-                    _ => {
-                        bail!(self.span(), "cannot destructure {}", value.type_name());
+                        i += sink_size as i64;
+                    } else {
+                        bail!(self.span(), "not enough elements to destructure")
                     }
                 }
-
-                Ok(Value::None)
+                ast::DestructuringKind::Named(named) => {
+                    bail!(named.span(), "cannot destructure named elements from an array")
+                }
+                ast::DestructuringKind::Placeholder(_) => i += 1,
             }
         }
+        if i < value.len() {
+            bail!(self.span(), "too many elements to destructure");
+        }
+
+        Ok(Value::None)
+    }
+
+    fn destruct_dict<T>(
+        &self,
+        vm: &mut Vm,
+        value: Dict,
+        f: T,
+        destruct: &ast::Destructuring,
+    ) -> SourceResult<Value>
+    where
+        T: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<Value>,
+    {
+        let mut sink = None;
+        let mut used = HashSet::new();
+        for p in destruct.bindings() {
+            match p {
+                ast::DestructuringKind::Normal(ast::Expr::Ident(ident)) => {
+                    let Ok(v) = value.at(&ident) else {
+                                        bail!(ident.span(), "destructuring key not found in dictionary");
+                                    };
+                    f(vm, ast::Expr::Ident(ident.clone()), v.clone())?;
+                    used.insert(ident.take());
+                }
+                ast::DestructuringKind::Sink(spread) => sink = spread.expr(),
+                ast::DestructuringKind::Named(named) => {
+                    let Ok(v) = value.at(named.name().as_str()) else {
+                                        bail!(named.name().span(), "destructuring key not found in dictionary");
+                                    };
+                    f(vm, named.expr(), v.clone())?;
+                    used.insert(named.name().take());
+                }
+                ast::DestructuringKind::Placeholder(_) => {}
+                ast::DestructuringKind::Normal(expr) => {
+                    bail!(expr.span(), "expected key, found expression");
+                }
+            }
+        }
+
+        if let Some(expr) = sink {
+            let mut sink = Dict::new();
+            for (key, value) in value {
+                if !used.contains(key.as_str()) {
+                    sink.insert(key, value);
+                }
+            }
+            f(vm, expr, Value::Dict(sink))?;
+        }
+
+        Ok(Value::None)
+    }
+
+    /// Destruct the given value into the pattern and apply the function to each binding.
+    #[tracing::instrument(skip_all)]
+    fn apply<T>(&self, vm: &mut Vm, value: Value, f: T) -> SourceResult<Value>
+    where
+        T: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<Value>,
+    {
+        match self {
+            ast::Pattern::Normal(expr) => {
+                f(vm, expr.clone(), value)?;
+                Ok(Value::None)
+            }
+            ast::Pattern::Placeholder(_) => Ok(Value::None),
+            ast::Pattern::Destructuring(destruct) => match value {
+                Value::Array(value) => self.destruct_array(vm, value, f, destruct),
+                Value::Dict(value) => self.destruct_dict(vm, value, f, destruct),
+                _ => bail!(self.span(), "cannot destructure {}", value.type_name()),
+            },
+        }
+    }
+
+    /// Destruct the value into the pattern by binding.
+    pub fn define(&self, vm: &mut Vm, value: Value) -> SourceResult<Value> {
+        self.apply(vm, value, |vm, expr, value| match expr {
+            ast::Expr::Ident(ident) => {
+                vm.define(ident, value);
+                Ok(Value::None)
+            }
+            _ => unreachable!(),
+        })
+    }
+
+    /// Destruct the value into the pattern by assignment.
+    pub fn assign(&self, vm: &mut Vm, value: Value) -> SourceResult<Value> {
+        self.apply(vm, value, |vm, expr, value| {
+            let location = expr.access(vm)?;
+            *location = value;
+            Ok(Value::None)
+        })
     }
 }
 
@@ -1345,6 +1390,16 @@ impl Eval for ast::LetBinding {
     }
 }
 
+impl Eval for ast::DestructAssignment {
+    type Output = Value;
+
+    fn eval(&self, vm: &mut Vm) -> SourceResult<Self::Output> {
+        let value = self.value().eval(vm)?;
+        self.pattern().assign(vm, value)?;
+        Ok(Value::None)
+    }
+}
+
 impl Eval for ast::SetRule {
     type Output = Styles;
 
@@ -1514,7 +1569,7 @@ impl Eval for ast::ForLoop {
         let pattern = self.pattern();
 
         match (&pattern, iter.clone()) {
-            (ast::Pattern::Ident(_), Value::Str(string)) => {
+            (ast::Pattern::Normal(_), Value::Str(string)) => {
                 // Iterate over graphemes of string.
                 iter!(for pattern in string.as_str().graphemes(true));
             }
@@ -1526,7 +1581,7 @@ impl Eval for ast::ForLoop {
                 // Iterate over values of array.
                 iter!(for pattern in array);
             }
-            (ast::Pattern::Ident(_), _) => {
+            (ast::Pattern::Normal(_), _) => {
                 bail!(self.iter().span(), "cannot loop over {}", iter.type_name());
             }
             (_, _) => {

src/ide/highlight.rs

@@ -246,6 +246,7 @@ pub fn highlight(node: &LinkedNode) -> Option<Tag> {
         SyntaxKind::LoopContinue => None,
         SyntaxKind::FuncReturn => None,
         SyntaxKind::Destructuring => None,
+        SyntaxKind::DestructAssignment => None,
 
         SyntaxKind::LineComment => Some(Tag::Comment),
         SyntaxKind::BlockComment => Some(Tag::Comment),

src/syntax/ast.rs

@@ -164,6 +164,8 @@ pub enum Expr {
     Closure(Closure),
     /// A let binding: `let x = 1`.
     Let(LetBinding),
+    //// A destructuring assignment: `(x, y) = (1, 2)`.
+    DestructAssign(DestructAssignment),
     /// A set rule: `set text(...)`.
     Set(SetRule),
     /// A show rule: `show heading: it => emph(it.body)`.
@@ -240,6 +242,7 @@ impl AstNode for Expr {
             SyntaxKind::FuncCall => node.cast().map(Self::FuncCall),
             SyntaxKind::Closure => node.cast().map(Self::Closure),
             SyntaxKind::LetBinding => node.cast().map(Self::Let),
+            SyntaxKind::DestructAssignment => node.cast().map(Self::DestructAssign),
             SyntaxKind::SetRule => node.cast().map(Self::Set),
             SyntaxKind::ShowRule => node.cast().map(Self::Show),
             SyntaxKind::Conditional => node.cast().map(Self::Conditional),
@@ -299,6 +302,7 @@ impl AstNode for Expr {
             Self::FuncCall(v) => v.as_untyped(),
             Self::Closure(v) => v.as_untyped(),
             Self::Let(v) => v.as_untyped(),
+            Self::DestructAssign(v) => v.as_untyped(),
             Self::Set(v) => v.as_untyped(),
             Self::Show(v) => v.as_untyped(),
             Self::Conditional(v) => v.as_untyped(),
@@ -1179,6 +1183,11 @@ impl Named {
     pub fn expr(&self) -> Expr {
         self.0.cast_last_match().unwrap_or_default()
     }
+
+    /// The right-hand side of the pair as an identifier.
+    pub fn expr_ident(&self) -> Option<Ident> {
+        self.0.cast_last_match()
+    }
 }
 
 node! {
@@ -1559,6 +1568,28 @@ impl Params {
     }
 }
 
+node! {
+    /// A spread: `..x` or `..x.at(0)`.
+    Spread
+}
+
+impl Spread {
+    /// Try to get an identifier.
+    pub fn name(&self) -> Option<Ident> {
+        self.0.cast_first_match()
+    }
+
+    /// Try to get an expression.
+    pub fn expr(&self) -> Option<Expr> {
+        self.0.cast_first_match()
+    }
+}
+
+node! {
+    /// An underscore: `_`
+    Underscore
+}
+
 /// A parameter to a closure.
 #[derive(Debug, Clone, Hash)]
 pub enum Param {
@@ -1567,9 +1598,9 @@ pub enum Param {
     /// A named parameter with a default value: `draw: false`.
     Named(Named),
     /// An argument sink: `..args`.
-    Sink(Option<Ident>),
+    Sink(Spread),
     /// A placeholder: `_`.
-    Placeholder,
+    Placeholder(Underscore),
 }
 
 impl AstNode for Param {
@@ -1577,8 +1608,8 @@ impl AstNode for Param {
         match node.kind() {
             SyntaxKind::Ident => node.cast().map(Self::Pos),
             SyntaxKind::Named => node.cast().map(Self::Named),
-            SyntaxKind::Spread => Some(Self::Sink(node.cast_first_match())),
-            SyntaxKind::Underscore => Some(Self::Placeholder),
+            SyntaxKind::Spread => node.cast().map(Self::Sink),
+            SyntaxKind::Underscore => node.cast().map(Self::Placeholder),
             _ => Option::None,
         }
     }
@@ -1587,8 +1618,8 @@ impl AstNode for Param {
         match self {
             Self::Pos(v) => v.as_untyped(),
             Self::Named(v) => v.as_untyped(),
-            Self::Sink(_) => self.as_untyped(),
-            Self::Placeholder => self.as_untyped(),
+            Self::Sink(v) => v.as_untyped(),
+            Self::Placeholder(v) => v.as_untyped(),
         }
     }
 }
@@ -1598,56 +1629,63 @@ node! {
     Destructuring
 }
 
-/// The kind of an element in a destructuring pattern.
-#[derive(Debug, Clone, Hash)]
-pub enum DestructuringKind {
-    /// An identifier: `x`.
-    Ident(Ident),
-    /// An argument sink: `..y`.
-    Sink(Option<Ident>),
-    /// Named arguments: `x: 1`.
-    Named(Ident, Ident),
-    /// A placeholder: `_`.
-    Placeholder,
-}
-
 impl Destructuring {
     /// The bindings of the destructuring.
     pub fn bindings(&self) -> impl Iterator<Item = DestructuringKind> + '_ {
-        self.0.children().filter_map(|child| match child.kind() {
-            SyntaxKind::Ident => {
-                Some(DestructuringKind::Ident(child.cast().unwrap_or_default()))
-            }
-            SyntaxKind::Spread => Some(DestructuringKind::Sink(child.cast_first_match())),
-            SyntaxKind::Named => {
-                let mut filtered = child.children().filter_map(SyntaxNode::cast);
-                let key = filtered.next().unwrap_or_default();
-                let ident = filtered.next().unwrap_or_default();
-                Some(DestructuringKind::Named(key, ident))
-            }
-            SyntaxKind::Underscore => Some(DestructuringKind::Placeholder),
-            _ => Option::None,
-        })
+        self.0.children().filter_map(SyntaxNode::cast)
     }
 
     // Returns a list of all identifiers in the pattern.
     pub fn idents(&self) -> impl Iterator<Item = Ident> + '_ {
         self.bindings().filter_map(|binding| match binding {
-            DestructuringKind::Ident(ident) => Some(ident),
-            DestructuringKind::Sink(ident) => ident,
-            DestructuringKind::Named(_, ident) => Some(ident),
-            DestructuringKind::Placeholder => Option::None,
+            DestructuringKind::Normal(Expr::Ident(ident)) => Some(ident),
+            DestructuringKind::Sink(spread) => spread.name(),
+            DestructuringKind::Named(named) => named.expr_ident(),
+            _ => Option::None,
         })
     }
 }
 
+/// The kind of an element in a destructuring pattern.
+#[derive(Debug, Clone, Hash)]
+pub enum DestructuringKind {
+    /// An expression: `x`.
+    Normal(Expr),
+    /// An argument sink: `..y`.
+    Sink(Spread),
+    /// Named arguments: `x: 1`.
+    Named(Named),
+    /// A placeholder: `_`.
+    Placeholder(Underscore),
+}
+
+impl AstNode for DestructuringKind {
+    fn from_untyped(node: &SyntaxNode) -> Option<Self> {
+        match node.kind() {
+            SyntaxKind::Named => node.cast().map(Self::Named),
+            SyntaxKind::Spread => node.cast().map(Self::Sink),
+            SyntaxKind::Underscore => node.cast().map(Self::Placeholder),
+            _ => node.cast().map(Self::Normal),
+        }
+    }
+
+    fn as_untyped(&self) -> &SyntaxNode {
+        match self {
+            Self::Normal(v) => v.as_untyped(),
+            Self::Named(v) => v.as_untyped(),
+            Self::Sink(v) => v.as_untyped(),
+            Self::Placeholder(v) => v.as_untyped(),
+        }
+    }
+}
+
 /// The kind of a pattern.
 #[derive(Debug, Clone, Hash)]
 pub enum Pattern {
-    /// A single identifier: `x`.
-    Ident(Ident),
+    /// A single expression: `x`.
+    Normal(Expr),
     /// A placeholder: `_`.
-    Placeholder,
+    Placeholder(Underscore),
     /// A destructuring pattern: `(x, _, ..y)`.
     Destructuring(Destructuring),
 }
@@ -1655,18 +1693,17 @@ pub enum Pattern {
 impl AstNode for Pattern {
     fn from_untyped(node: &SyntaxNode) -> Option<Self> {
         match node.kind() {
-            SyntaxKind::Ident => node.cast().map(Self::Ident),
             SyntaxKind::Destructuring => node.cast().map(Self::Destructuring),
-            SyntaxKind::Underscore => Some(Self::Placeholder),
-            _ => Option::None,
+            SyntaxKind::Underscore => node.cast().map(Self::Placeholder),
+            _ => node.cast().map(Self::Normal),
         }
     }
 
     fn as_untyped(&self) -> &SyntaxNode {
         match self {
-            Self::Ident(v) => v.as_untyped(),
+            Self::Normal(v) => v.as_untyped(),
             Self::Destructuring(v) => v.as_untyped(),
-            Self::Placeholder => self.as_untyped(),
+            Self::Placeholder(v) => v.as_untyped(),
         }
     }
 }
@@ -1675,16 +1712,16 @@ impl Pattern {
     // Returns a list of all identifiers in the pattern.
     pub fn idents(&self) -> Vec<Ident> {
         match self {
-            Pattern::Ident(ident) => vec![ident.clone()],
+            Pattern::Normal(Expr::Ident(ident)) => vec![ident.clone()],
             Pattern::Destructuring(destruct) => destruct.idents().collect(),
-            Pattern::Placeholder => vec![],
+            _ => vec![],
         }
     }
 }
 
 impl Default for Pattern {
     fn default() -> Self {
-        Self::Ident(Ident::default())
+        Self::Normal(Expr::default())
     }
 }
 
@@ -1716,23 +1753,18 @@ impl LetBindingKind {
 impl LetBinding {
     /// The kind of the let binding.
     pub fn kind(&self) -> LetBindingKind {
-        if let Some(pattern) = self.0.cast_first_match::<Pattern>() {
-            LetBindingKind::Normal(pattern)
-        } else {
-            LetBindingKind::Closure(
-                self.0
-                    .cast_first_match::<Closure>()
-                    .unwrap_or_default()
-                    .name()
-                    .unwrap_or_default(),
-            )
+        match self.0.cast_first_match::<Pattern>() {
+            Some(Pattern::Normal(Expr::Closure(closure))) => {
+                LetBindingKind::Closure(closure.name().unwrap_or_default())
+            }
+            pattern => LetBindingKind::Normal(pattern.unwrap_or_default()),
         }
     }
 
     /// The expression the binding is initialized with.
     pub fn init(&self) -> Option<Expr> {
         match self.kind() {
-            LetBindingKind::Normal(Pattern::Ident(_)) => {
+            LetBindingKind::Normal(Pattern::Normal(_)) => {
                 self.0.children().filter_map(SyntaxNode::cast).nth(1)
             }
             LetBindingKind::Normal(_) => self.0.cast_first_match(),
@@ -1741,6 +1773,23 @@ impl LetBinding {
     }
 }
 
+node! {
+    /// An assignment expression `(x, y) = (1, 2)`.
+    DestructAssignment
+}
+
+impl DestructAssignment {
+    /// The pattern of the assignment.
+    pub fn pattern(&self) -> Pattern {
+        self.0.cast_first_match::<Pattern>().unwrap_or_default()
+    }
+
+    /// The expression that is assigned.
+    pub fn value(&self) -> Expr {
+        self.0.cast_last_match().unwrap_or_default()
+    }
+}
+
 node! {
     /// A set rule: `set text(...)`.
     SetRule

src/syntax/kind.rs

@@ -244,6 +244,8 @@ pub enum SyntaxKind {
     FuncReturn,
     /// A destructuring pattern: `(x, _, ..y)`.
     Destructuring,
+    /// A destructuring assignment expression: `(x, y) = (1, 2)`.
+    DestructAssignment,
 
     /// A line comment: `// ...`.
     LineComment,
@@ -430,6 +432,7 @@ impl SyntaxKind {
             Self::LoopContinue => "`continue` expression",
             Self::FuncReturn => "`return` expression",
             Self::Destructuring => "destructuring pattern",
+            Self::DestructAssignment => "destructuring assignment expression",
             Self::LineComment => "line comment",
             Self::BlockComment => "block comment",
             Self::Error => "syntax error",

src/syntax/parser.rs

@@ -725,7 +725,16 @@ fn with_paren(p: &mut Parser) {
         p.assert(SyntaxKind::Arrow);
         code_expr(p);
         kind = SyntaxKind::Closure;
+    } else if p.at(SyntaxKind::Eq) && kind != SyntaxKind::Parenthesized {
+        // TODO: add warning if p.at(SyntaxKind::Eq) && kind == SyntaxKind::Parenthesized
+
+        validate_destruct_pattern(p, m, false);
+        p.wrap(m, SyntaxKind::Destructuring);
+        p.assert(SyntaxKind::Eq);
+        code_expr(p);
+        kind = SyntaxKind::DestructAssignment;
     }
+
     match kind {
         SyntaxKind::Array => validate_array(p, m),
         SyntaxKind::Dict => validate_dict(p, m),
@@ -866,7 +875,7 @@ fn pattern(p: &mut Parser) -> PatternKind {
     let m = p.marker();
     if p.at(SyntaxKind::LeftParen) {
         let kind = collection(p, false);
-        validate_destruct_pattern(p, m);
+        validate_destruct_pattern(p, m, true);
 
         if kind == SyntaxKind::Parenthesized {
             PatternKind::Ident
@@ -1184,7 +1193,7 @@ fn validate_args(p: &mut Parser, m: Marker) {
     }
 }
 
-fn validate_destruct_pattern(p: &mut Parser, m: Marker) {
+fn validate_destruct_pattern(p: &mut Parser, m: Marker, forbid_expressions: bool) {
     let mut used_spread = false;
     let mut used = HashSet::new();
     for child in p.post_process(m) {
@@ -1206,7 +1215,7 @@ fn validate_destruct_pattern(p: &mut Parser, m: Marker) {
 
                 if within.kind() == SyntaxKind::Dots {
                     continue;
-                } else if within.kind() != SyntaxKind::Ident {
+                } else if forbid_expressions && within.kind() != SyntaxKind::Ident {
                     within.convert_to_error(eco_format!(
                         "expected identifier, found {}",
                         within.kind().name(),
@@ -1231,15 +1240,17 @@ fn validate_destruct_pattern(p: &mut Parser, m: Marker) {
                     child.make_erroneous();
                 }
 
-                let Some(within) = child.children_mut().last_mut() else { return };
-                if within.kind() != SyntaxKind::Ident
-                    && within.kind() != SyntaxKind::Underscore
-                {
-                    within.convert_to_error(eco_format!(
-                        "expected identifier, found {}",
-                        within.kind().name(),
-                    ));
-                    child.make_erroneous();
+                if forbid_expressions {
+                    let Some(within) = child.children_mut().last_mut() else { return };
+                    if within.kind() != SyntaxKind::Ident
+                        && within.kind() != SyntaxKind::Underscore
+                    {
+                        within.convert_to_error(eco_format!(
+                            "expected identifier, found {}",
+                            within.kind().name(),
+                        ));
+                        child.make_erroneous();
+                    }
                 }
             }
             SyntaxKind::LeftParen
@@ -1247,10 +1258,12 @@ fn validate_destruct_pattern(p: &mut Parser, m: Marker) {
             | SyntaxKind::Comma
             | SyntaxKind::Underscore => {}
             kind => {
-                child.convert_to_error(eco_format!(
-                    "expected identifier or destructuring sink, found {}",
-                    kind.name()
-                ));
+                if forbid_expressions {
+                    child.convert_to_error(eco_format!(
+                        "expected identifier or destructuring sink, found {}",
+                        kind.name()
+                    ));
+                }
             }
         }
     }

tests/typ/compiler/let.typ

@@ -121,6 +121,12 @@ Three
 // Error: 13-14 at most one binding per identifier is allowed
 #let (a: a, a) = (a: 1, b: 2)
 
+// Error: 13-20 expected identifier, found function call
+#let (a, b: b.at(0)) = (a: 1, b: 2)
+
+// Error: 7-14 expected identifier or destructuring sink, found function call
+#let (a.at(0),) = (1,)
+
 ---
 // Error: 13-14 not enough elements to destructure
 #let (a, b, c) = (1, 2)
@@ -181,11 +187,11 @@ Three
 #let (a, b) = (a: 1)
 
 ---
-// Error: 13-14 destructuring key not found in dictionary
+// Error: 10-11 destructuring key not found in dictionary
 #let (a, b: b) = (a: 1)
 
 ---
-// Error: 7-8 cannot destructure named elements from an array
+// Error: 7-11 cannot destructure named elements from an array
 #let (a: a, b) = (1, 2, 3)
 
 ---

tests/typ/compiler/ops-invalid.typ

@@ -100,6 +100,10 @@
 // Error: 4-5 unknown variable: x
 #((x) = "")
 
+---
+// Error: 4-5 unknown variable: x
+#((x,) = (1,))
+
 ---
 // Error: 3-8 cannot mutate a temporary value
 #(1 + 2 += 3)

tests/typ/compiler/ops.typ

@@ -200,6 +200,48 @@
 #(x = "some")   #test(x, "some")
 #(x += "thing") #test(x, "something")
 
+---
+// Test destructuring assignments.
+
+#let a = none
+#let b = none
+#let c = none
+#((a,) = (1,))
+#test(a, 1)
+
+#((_, a, b, _) = (1, 2, 3, 4))
+#test(a, 2)
+#test(b, 3)
+
+#((a, b, ..c) = (1, 2, 3, 4, 5, 6))
+#test(a, 1)
+#test(b, 2)
+#test(c, (3, 4, 5, 6))
+
+#((a: a, b, x: c) = (a: 1, b: 2, x: 3))
+#test(a, 1)
+#test(b, 2)
+#test(c, 3)
+
+#let a = (1, 2)
+#((a: a.at(0), b) = (a: 3, b: 4))
+#test(a, (3, 2))
+#test(b, 4)
+
+#let a = (1, 2)
+#((a.at(0), b) = (3, 4))
+#test(a, (3, 2))
+#test(b, 4)
+
+#((a, ..b) = (1, 2, 3, 4))
+#test(a, 1)
+#test(b, (2, 3, 4))
+
+#let a = (1, 2)
+#((b, ..a.at(0)) = (1, 2, 3, 4))
+#test(a, ((2, 3, 4), 2))
+#test(b, 1)
+
 ---
 // Error: 3-6 cannot mutate a constant: box
 #(box = 1)