fix parenthesized binding (typst#707)

Author: Marmare314

docs/src/reference/scripting.md

@@ -96,7 +96,7 @@ The last element is #b.
   "Homer": "The Odyssey",
   "Austen": "Persuasion",
 )
-#let (Austen) = books
+#let (Austen,) = books
 Austen wrote #Austen.
 
 #let (Homer: h) = books

src/syntax/ast.rs

@@ -1620,7 +1620,14 @@ pub enum DestructuringKind {
 impl Pattern {
     /// The kind of the pattern.
     pub fn kind(&self) -> PatternKind {
-        if self.0.children().len() <= 1 {
+        if self
+            .0
+            .children()
+            .map(SyntaxNode::kind)
+            .skip_while(|&kind| kind == SyntaxKind::LeftParen)
+            .take_while(|&kind| kind != SyntaxKind::RightParen)
+            .eq([SyntaxKind::Ident])
+        {
             return PatternKind::Ident(self.0.cast_first_match().unwrap_or_default());
         }
 

src/syntax/parser.rs

@@ -847,11 +847,15 @@ fn pattern(p: &mut Parser) -> PatternKind {
     let m = p.marker();
 
     if p.at(SyntaxKind::LeftParen) {
-        collection(p, false);
+        let kind = collection(p, false);
         validate_destruct_pattern(p, m);
         p.wrap(m, SyntaxKind::Pattern);
 
-        PatternKind::Destructuring
+        if kind == SyntaxKind::Parenthesized {
+            PatternKind::Normal
+        } else {
+            PatternKind::Destructuring
+        }
     } else {
         if p.expect(SyntaxKind::Ident) {
             p.wrap(m, SyntaxKind::Pattern);

tests/typ/compiler/let.typ

@@ -32,13 +32,23 @@ Three
 #test(v2, 2)
 #test(v3, 3)
 
+---
+// Test parenthesised assignments.
+// Ref: false
+#let (a) = (1, 2)
+
 ---
 // Ref: false
 // Simple destructuring.
 #let (a, b) = (1, 2)
 #test(a, 1)
 #test(b, 2)
 
+---
+// Ref: false
+#let (a,) = (1,)
+#test(a, 1)
+
 ---
 // Ref: false
 // Destructuring with multiple placeholders.
@@ -115,10 +125,6 @@ Three
 // Error: 13-14 not enough elements to destructure
 #let (a, b, c) = (1, 2)
 
----
-// Error: 6-9 too many elements to destructure
-#let (a) = (1, 2)
-
 ---
 // Error: 6-20 not enough elements to destructure
 #let (..a, b, c, d) = (1, 2)