Pattern as parameter (#854)

src/eval/func.rs

@@ -276,13 +276,11 @@ pub(super) struct Closure {
 #[derive(Hash)]
 pub enum Param {
     /// A positional parameter: `x`.
-    Pos(Ident),
+    Pos(ast::Pattern),
     /// A named parameter with a default value: `draw: false`.
     Named(Ident, Value),
     /// An argument sink: `..args`.
     Sink(Option<Ident>),
-    /// A placeholder: `_`.
-    Placeholder,
 }
 
 impl Closure {
@@ -330,9 +328,18 @@ impl Closure {
         let mut sink_pos_values = None;
         for p in &closure.params {
             match p {
-                Param::Pos(ident) => {
-                    vm.define(ident.clone(), args.expect::<Value>(ident)?);
-                }
+                Param::Pos(pattern) => match pattern {
+                    ast::Pattern::Normal(ast::Expr::Ident(ident)) => {
+                        vm.define(ident.clone(), args.expect::<Value>(ident)?)
+                    }
+                    ast::Pattern::Normal(_) => unreachable!(),
+                    _ => {
+                        pattern.define(
+                            &mut vm,
+                            args.expect::<Value>("pattern parameter")?,
+                        )?;
+                    }
+                },
                 Param::Sink(ident) => {
                     sink = ident.clone();
                     if let Some(sink_size) = sink_size {
@@ -344,9 +351,6 @@ impl Closure {
                         args.named::<Value>(ident)?.unwrap_or_else(|| default.clone());
                     vm.define(ident.clone(), value);
                 }
-                Param::Placeholder => {
-                    args.eat::<Value>()?;
-                }
             }
         }
 
@@ -443,12 +447,15 @@ impl<'a> CapturesVisitor<'a> {
 
                 for param in expr.params().children() {
                     match param {
-                        ast::Param::Pos(ident) => self.bind(ident),
+                        ast::Param::Pos(pattern) => {
+                            for ident in pattern.idents() {
+                                self.bind(ident);
+                            }
+                        }
                         ast::Param::Named(named) => self.bind(named.name()),
                         ast::Param::Sink(spread) => {
                             self.bind(spread.name().unwrap_or_default())
                         }
-                        _ => {}
                     }
                 }
 

src/eval/mod.rs

@@ -1207,14 +1207,11 @@ impl Eval for ast::Closure {
         let mut params = Vec::new();
         for param in self.params().children() {
             match param {
-                ast::Param::Pos(name) => {
-                    params.push(Param::Pos(name));
-                }
+                ast::Param::Pos(pattern) => params.push(Param::Pos(pattern)),
                 ast::Param::Named(named) => {
                     params.push(Param::Named(named.name(), named.expr().eval(vm)?));
                 }
                 ast::Param::Sink(spread) => params.push(Param::Sink(spread.name())),
-                ast::Param::Placeholder(_) => params.push(Param::Placeholder),
             }
         }
 

src/syntax/ast.rs

@@ -1594,23 +1594,19 @@ node! {
 #[derive(Debug, Clone, Hash)]
 pub enum Param {
     /// A positional parameter: `x`.
-    Pos(Ident),
+    Pos(Pattern),
     /// A named parameter with a default value: `draw: false`.
     Named(Named),
     /// An argument sink: `..args`.
     Sink(Spread),
-    /// A placeholder: `_`.
-    Placeholder(Underscore),
 }
 
 impl AstNode for Param {
     fn from_untyped(node: &SyntaxNode) -> Option<Self> {
         match node.kind() {
-            SyntaxKind::Ident => node.cast().map(Self::Pos),
             SyntaxKind::Named => node.cast().map(Self::Named),
             SyntaxKind::Spread => node.cast().map(Self::Sink),
-            SyntaxKind::Underscore => node.cast().map(Self::Placeholder),
-            _ => Option::None,
+            _ => node.cast().map(Self::Pos),
         }
     }
 
@@ -1619,7 +1615,6 @@ impl AstNode for Param {
             Self::Pos(v) => v.as_untyped(),
             Self::Named(v) => v.as_untyped(),
             Self::Sink(v) => v.as_untyped(),
-            Self::Placeholder(v) => v.as_untyped(),
         }
     }
 }

src/syntax/parser.rs

@@ -523,7 +523,11 @@ fn code(p: &mut Parser, mut stop: impl FnMut(SyntaxKind) -> bool) {
 }
 
 fn code_expr(p: &mut Parser) {
-    code_expr_prec(p, false, 0)
+    code_expr_prec(p, false, 0, false)
+}
+
+fn code_expr_or_pattern(p: &mut Parser) {
+    code_expr_prec(p, false, 0, true)
 }
 
 fn embedded_code_expr(p: &mut Parser) {
@@ -542,7 +546,7 @@ fn embedded_code_expr(p: &mut Parser) {
     );
 
     let prev = p.prev_end();
-    code_expr_prec(p, true, 0);
+    code_expr_prec(p, true, 0, false);
 
     // Consume error for things like `#12p` or `#"abc\"`.
     if !p.progress(prev) {
@@ -560,14 +564,19 @@ fn embedded_code_expr(p: &mut Parser) {
     p.unstop();
 }
 
-fn code_expr_prec(p: &mut Parser, atomic: bool, min_prec: usize) {
+fn code_expr_prec(
+    p: &mut Parser,
+    atomic: bool,
+    min_prec: usize,
+    allow_destructuring: bool,
+) {
     let m = p.marker();
     if let (false, Some(op)) = (atomic, ast::UnOp::from_kind(p.current())) {
         p.eat();
-        code_expr_prec(p, atomic, op.precedence());
+        code_expr_prec(p, atomic, op.precedence(), false);
         p.wrap(m, SyntaxKind::Unary);
     } else {
-        code_primary(p, atomic);
+        code_primary(p, atomic, allow_destructuring);
     }
 
     loop {
@@ -615,7 +624,7 @@ fn code_expr_prec(p: &mut Parser, atomic: bool, min_prec: usize) {
             }
 
             p.eat();
-            code_expr_prec(p, false, prec);
+            code_expr_prec(p, false, prec, false);
             p.wrap(m, SyntaxKind::Binary);
             continue;
         }
@@ -624,7 +633,7 @@ fn code_expr_prec(p: &mut Parser, atomic: bool, min_prec: usize) {
     }
 }
 
-fn code_primary(p: &mut Parser, atomic: bool) {
+fn code_primary(p: &mut Parser, atomic: bool, allow_destructuring: bool) {
     let m = p.marker();
     match p.current() {
         SyntaxKind::Ident => {
@@ -650,7 +659,7 @@ fn code_primary(p: &mut Parser, atomic: bool) {
 
         SyntaxKind::LeftBrace => code_block(p),
         SyntaxKind::LeftBracket => content_block(p),
-        SyntaxKind::LeftParen => with_paren(p),
+        SyntaxKind::LeftParen => with_paren(p, allow_destructuring),
         SyntaxKind::Dollar => equation(p),
         SyntaxKind::Let => let_binding(p),
         SyntaxKind::Set => set_rule(p),
@@ -716,7 +725,7 @@ fn content_block(p: &mut Parser) {
     p.wrap(m, SyntaxKind::ContentBlock);
 }
 
-fn with_paren(p: &mut Parser) {
+fn with_paren(p: &mut Parser, allow_destructuring: bool) {
     let m = p.marker();
     let mut kind = collection(p, true);
     if p.at(SyntaxKind::Arrow) {
@@ -739,11 +748,37 @@ fn with_paren(p: &mut Parser) {
         SyntaxKind::Array => validate_array(p, m),
         SyntaxKind::Dict => validate_dict(p, m),
         SyntaxKind::Parenthesized => validate_parenthesized(p, m),
+        SyntaxKind::Destructuring if !allow_destructuring => {
+            invalidate_destructuring(p, m)
+        }
         _ => {}
     }
     p.wrap(m, kind);
 }
 
+fn invalidate_destructuring(p: &mut Parser, m: Marker) {
+    let mut collection_kind = Option::None;
+    for child in p.post_process(m) {
+        match child.kind() {
+            SyntaxKind::Named | SyntaxKind::Keyed => match collection_kind {
+                Some(SyntaxKind::Array) => child.convert_to_error(eco_format!(
+                    "expected expression, found {}",
+                    child.kind().name()
+                )),
+                _ => collection_kind = Some(SyntaxKind::Dict),
+            },
+            SyntaxKind::LeftParen | SyntaxKind::RightParen | SyntaxKind::Comma => {}
+            kind => match collection_kind {
+                Some(SyntaxKind::Dict) => child.convert_to_error(eco_format!(
+                    "expected named or keyed pair, found {}",
+                    kind.name()
+                )),
+                _ => collection_kind = Some(SyntaxKind::Array),
+            },
+        }
+    }
+}
+
 fn collection(p: &mut Parser, keyed: bool) -> SyntaxKind {
     p.stop_at_newline(false);
     p.assert(SyntaxKind::LeftParen);
@@ -760,10 +795,17 @@ fn collection(p: &mut Parser, keyed: bool) -> SyntaxKind {
         let prev = p.prev_end();
         match item(p, keyed) {
             SyntaxKind::Spread => parenthesized = false,
-            SyntaxKind::Named | SyntaxKind::Keyed if kind.is_none() => {
-                kind = Some(SyntaxKind::Dict);
+            SyntaxKind::Named | SyntaxKind::Keyed => {
+                match kind {
+                    Some(SyntaxKind::Array) => kind = Some(SyntaxKind::Destructuring),
+                    _ => kind = Some(SyntaxKind::Dict),
+                }
                 parenthesized = false;
             }
+            SyntaxKind::Int => match kind {
+                Some(SyntaxKind::Array) | None => kind = Some(SyntaxKind::Array),
+                Some(_) => kind = Some(SyntaxKind::Destructuring),
+            },
             _ if kind.is_none() => kind = Some(SyntaxKind::Array),
             _ => {}
         }
@@ -809,7 +851,7 @@ fn item(p: &mut Parser, keyed: bool) -> SyntaxKind {
     }
 
     if !p.eat_if(SyntaxKind::Underscore) {
-        code_expr(p);
+        code_expr_or_pattern(p);
     } else {
         return SyntaxKind::Underscore;
     }
@@ -1161,6 +1203,10 @@ fn validate_params(p: &mut Parser, m: Marker) {
                     child.make_erroneous();
                 }
             }
+            SyntaxKind::Array | SyntaxKind::Dict | SyntaxKind::Destructuring => {
+                validate_pattern(child.children_mut().iter_mut(), &mut used, false);
+                child.convert_to_kind(SyntaxKind::Destructuring);
+            }
             SyntaxKind::LeftParen
             | SyntaxKind::RightParen
             | SyntaxKind::Comma
@@ -1194,9 +1240,17 @@ fn validate_args(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) {
+    validate_pattern(p.post_process(m), &mut used, forbid_expressions);
+}
+
+fn validate_pattern<'a>(
+    children: impl Iterator<Item = &'a mut SyntaxNode>,
+    used: &mut HashSet<EcoString>,
+    forbid_expressions: bool,
+) {
+    let mut used_spread = false;
+    for child in children {
         match child.kind() {
             SyntaxKind::Ident => {
                 if !used.insert(child.text().clone()) {

tests/typ/compiler/closure.typ

@@ -145,6 +145,29 @@
   test(greet("Typst", whatever: 10))
 }
 
+---
+// Parameter unpacking.
+#let f((a, b), ..c) = (a, b, c)
+#test(f((1, 2), 3, 4), (1, 2, (3, 4)))
+
+#let f((k: a, b), c: 3, (d,)) = (a, b, c, d)
+#test(f((k: 1, b: 2), (4,)), (1, 2, 3, 4))
+
+// Error: 22-23 duplicate parameter: a
+#let f((a: b), (c,), a) = none
+
+// Error: 8-14 expected identifier, found array
+#let f((a, b): 0) = none
+
+// Error: 10-19 expected identifier, found destructuring pattern
+#let f(..(a, b: c)) = none
+
+// Error: 10-16 expected identifier, found array
+#let f(..(a, b)) = none
+
+// Error: 10-19 expected identifier, found destructuring pattern
+#let f(..(a, b: c)) = none
+
 ---
 // Error: 11-12 duplicate parameter: x
 #let f(x, x) = none