Unpacking syntax (#532)

Closes #341

4 files changed, 170 insertions, 10 deletions

diff --git a/tests/typ/compiler/for.typ b/tests/typ/compiler/for.typ
index 7833aad7..1c780710 100644
--- a/tests/typ/compiler/for.typ
+++ b/tests/typ/compiler/for.typ
@@ -9,7 +9,7 @@
 
 // Dictionary is not traversed in insertion order.
 // Should output `Age: 2. Name: Typst.`.
-#for k, v in (Name: "Typst", Age: 2) [
+#for (k, v) in (Name: "Typst", Age: 2) [
   #k: #v.
 ]
 
@@ -47,22 +47,22 @@
 }
 
 // Indices and values of array.
-#for i, v in ("1", "2", "3") {
+#for (i, v) in ("1", "2", "3").enumerate() {
   test(repr(i + 1), v)
 }
 
-// Values of dictionary.
+// Pairs of dictionary.
 #for v in (a: 4, b: 5) {
   out += (v,)
 }
 
 // Keys and values of dictionary.
-#for k, v in (a: 6, b: 7) {
+#for (k, v) in (a: 6, b: 7) {
   out += (k,)
   out += (v,)
 }
 
-#test(out, (1, 2, 3, 4, 5, "a", 6, "b", 7))
+#test(out, (1, 2, 3, ("a", 4), ("b", 5), "a", 6, "b", 7))
 
 // Grapheme clusters of string.
 #let first = true
@@ -85,12 +85,19 @@
 
 ---
 // Keys and values of strings.
-// Error: 6-10 mismatched pattern
-#for k, v in "hi" {
+// Error: 6-12 cannot destructure values of string
+#for (k, v) in "hi" {
   dont-care
 }
 
 ---
+// Destructuring without parentheses.
+// Error: 7 expected keyword `in`. did you mean to use a destructuring pattern?
+// Error: 7 expected keyword `in`
+#for k, v in (a: 4, b: 5) {
+  dont-care
+}
+
 // Error: 5 expected identifier
 #for
 
diff --git a/tests/typ/compiler/let.typ b/tests/typ/compiler/let.typ
index aa1132b9..4518f3d4 100644
--- a/tests/typ/compiler/let.typ
+++ b/tests/typ/compiler/let.typ
@@ -33,6 +33,156 @@ Three
 #test(v3, 3)
 
 ---
+// Ref: false
+// Simple destructuring.
+#let (a, b) = (1, 2)
+#test(a, 1)
+#test(b, 2)
+
+---
+// Ref: false
+// Destructuring with multiple placeholders.
+#let (a, _, c, _) = (1, 2, 3, 4)
+#test(a, 1)
+#test(c, 3)
+
+---
+// Ref: false
+// Destructuring with a sink.
+#let (a, b, ..c) = (1, 2, 3, 4, 5, 6)
+#test(a, 1)
+#test(b, 2)
+#test(c, (3, 4, 5, 6))
+
+---
+// Ref: false
+// Destructuring with a sink in the middle.
+#let (a, ..b, c) = (1, 2, 3, 4, 5, 6)
+#test(a, 1)
+#test(b, (2, 3, 4, 5))
+#test(c, 6)
+
+---
+// Ref: false
+// Destructuring with an empty sink.
+#let (..a, b, c) = (1, 2)
+#test(a, ())
+#test(b, 1)
+#test(c, 2)
+
+---
+// Ref: false
+// Destructuring with an empty sink.
+#let (a, ..b, c) = (1, 2)
+#test(a, 1)
+#test(b, ())
+#test(c, 2)
+
+---
+// Ref: false
+// Destructuring with an empty sink.
+#let (a, b, ..c) = (1, 2)
+#test(a, 1)
+#test(b, 2)
+#test(c, ())
+
+---
+// Ref: false
+// Destructuring with an empty sink and empty array.
+#let (..a) = ()
+#test(a, ())
+
+---
+// Ref: false
+// Destructuring with unnamed sink.
+#let (a, .., b) = (1, 2, 3, 4)
+#test(a, 1)
+#test(b, 4)
+
+// Error: 10-11 at most one binding per identifier is allowed
+#let (a, a) = (1, 2)
+
+// Error: 12-15 at most one destructuring sink is allowed
+#let (..a, ..a) = (1, 2)
+
+// Error: 12-13 at most one binding per identifier is allowed
+#let (a, ..a) = (1, 2)
+
+// Error: 13-14 at most one binding per identifier is allowed
+#let (a: a, a) = (a: 1, b: 2)
+
+---
+// 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)
+
+---
+// Error: 6-12 cannot destructure boolean
+#let (a, b) = true
+
+---
+// Ref: false
+// Simple destructuring.
+#let (a: a, b, x: c) = (a: 1, b: 2, x: 3)
+#test(a, 1)
+#test(b, 2)
+#test(c, 3)
+
+---
+// Ref: false
+// Destructuring with a sink.
+#let (a: _, ..b) = (a: 1, b: 2, c: 3)
+#test(b, (b: 2, c: 3))
+
+---
+// Ref: false
+// Destructuring with a sink in the middle.
+#let (a: _, ..b, c: _) = (a: 1, b: 2, c: 3)
+#test(b, (b: 2))
+
+---
+// Ref: false
+// Destructuring with an empty sink.
+#let (a: _, ..b) = (a: 1)
+#test(b, (:))
+
+---
+// Ref: false
+// Destructuring with an empty sink and empty dict.
+#let (..a) = (:)
+#test(a, (:))
+
+---
+// Ref: false
+// Destructuring with unnamed sink.
+#let (a, ..) = (a: 1, b: 2)
+#test(a, 1)
+
+---
+// Error: 10-13 expected identifier, found string
+// Error: 18-19 expected identifier, found integer
+#let (a: "a", b: 2) = (a: 1, b: 2)
+
+---
+// Error: 10-11 destructuring key not found in dictionary
+#let (a, b) = (a: 1)
+
+---
+// Error: 13-14 destructuring key not found in dictionary
+#let (a, b: b) = (a: 1)
+
+---
+// Error: 7-8 cannot destructure named elements from an array
+#let (a: a, b) = (1, 2, 3)
+
+---
 // Error: 5 expected identifier
 #let
 
@@ -62,6 +212,9 @@ Three
 // Error: 18 expected closing paren
 #let v5 = (1, 2 + ; Five
 
+// Error: 9-13 expected identifier, found boolean
+#let (..true) = false
+
 ---
 // Error: 13 expected equals sign
 #let func(x)
diff --git a/tests/typ/layout/stack-1.typ b/tests/typ/layout/stack-1.typ
index 864a06df..8b5472e8 100644
--- a/tests/typ/layout/stack-1.typ
+++ b/tests/typ/layout/stack-1.typ
@@ -12,7 +12,7 @@
   rect(width: w, height: 10pt, fill: rgb(v, v, v))
 }
 
-#let items = for i, w in widths {
+#let items = for (i, w) in widths.enumerate() {
   (align(right, shaded(i, w)),)
 }
 
diff --git a/tests/typ/visualize/shape-fill-stroke.typ b/tests/typ/visualize/shape-fill-stroke.typ
index 24ace85b..0d133171 100644
--- a/tests/typ/visualize/shape-fill-stroke.typ
+++ b/tests/typ/visualize/shape-fill-stroke.typ
@@ -2,7 +2,7 @@
 
 ---
 #let variant = rect.with(width: 20pt, height: 10pt)
-#let items = for i, item in (
+#let items = for (i, item) in (
   variant(stroke: none),
   variant(),
   variant(fill: none),
@@ -15,7 +15,7 @@
   variant(fill: forest, stroke: conifer),
   variant(fill: forest, stroke: black + 2pt),
   variant(fill: forest, stroke: conifer + 2pt),
-) {
+).enumerate() {
   (align(horizon)[#(i + 1).], item, [])
 }