From e9c2959dda139f4bbc19b60fd2bf6a216803f4db Mon Sep 17 00:00:00 2001
From: Erik Demaine <edemaine@mit.edu>
Date: Sat, 2 Nov 2024 15:44:20 -0400
Subject: [PATCH] Fix `for key: T, value in` loop to define `value` using typed
 `key`

Helps with #1562
---
 civet.dev/reference.md  |  5 ++---
 source/parser/for.civet | 14 ++++++++++----
 test/types/for.civet    | 13 ++++++++++++-
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/civet.dev/reference.md b/civet.dev/reference.md
index af8db6f5..13aa3afd 100644
--- a/civet.dev/reference.md
+++ b/civet.dev/reference.md
@@ -1758,9 +1758,8 @@ for own key in object
 You can add types to the declarations (unlike TypeScript):
 
 <Playground>
-for var key: string, value: unknown in object
-  console.log key, JSON.stringify value
-key ?= "no last key"
+for key: keyof typeof object, value in object
+  process key, value
 </Playground>
 
 ### Loop Expressions
diff --git a/source/parser/for.civet b/source/parser/for.civet
index 55f50979..cab4fbc1 100644
--- a/source/parser/for.civet
+++ b/source/parser/for.civet
@@ -338,17 +338,18 @@ function processForInOf($0: [
       children: [declaration, " = ", itemRef]
       names: declaration.names
     }, ";"]
-    pattern = itemRef
     declaration =
       type: "ForDeclaration"
       binding: {
         type: "Binding"
-        pattern
-        children: [ pattern ]
+        pattern: itemRef
+        children: [ itemRef ]
         names: []
       }
       children: ["const ", itemRef]
       names: []
+    unless pattern.type is "Identifier"
+      pattern = itemRef
 
   unless declaration2 or own
     return {
@@ -392,7 +393,12 @@ function processForInOf($0: [
       if decl2
         blockPrefix.push ["", {
           type: "Declaration"
-          children: [trimFirstSpace(ws2), decl2, " = ", trimFirstSpace(expRef), "[", trimFirstSpace(pattern), "]"]
+          children: [
+            trimFirstSpace(ws2), decl2, " = "
+            trimFirstSpace(expRef)
+            "[", trimFirstSpace(pattern), "]"
+          ]
+          decl: decl2
           names: decl2.names
         }, ";"]
 
diff --git a/test/types/for.civet b/test/types/for.civet
index 8641de33..3e39967d 100644
--- a/test/types/for.civet
+++ b/test/types/for.civet
@@ -51,11 +51,22 @@ describe "[TS] for", ->
     for x: T, y in z
       console.log x, y
     ---
-    for (const key in z) {const x: T = key;const y = z[key];
+    for (const key in z) {const x: T = key;const y = z[x];
       console.log(x, y)
     }
   """
 
+  testCase """
+    destructuring for..in with two declarations
+    ---
+    for [a, b]: T, value in z
+      console.log x
+    ---
+    for (const key in z) {const [a, b]: T = key;const value = z[key];
+      console.log(x)
+    }
+  """
+
   testCase """
     parenthesized
     ---