Fix scoping

hkmc2/shared/src/main/scala/hkmc2/codegen/js/JSBuilder.scala

@@ -318,9 +318,9 @@ class JSBuilder extends CodeBuilder:
       )
 
   def block(t: Block)(using Raise, Scope): Document =
-    if t.definedVars.isEmpty then returningTerm(t).stripBreaks else
-      val vars = t.definedVars.toSeq.sortBy(_.uid).iterator.map(l =>
-        l -> scope.allocateName(l))
+    val vars = t.definedVars.toSeq.filter(scope.lookup(_).isEmpty).sortBy(_.uid).iterator.map(l =>
+      l -> scope.allocateName(l))
+    if vars.isEmpty then returningTerm(t).stripBreaks else
       doc"let " :: vars.map: (_, nme) =>
         nme
       .toList.mkDocument(", ")

hkmc2/shared/src/test/mlscript/codegen/Scoping.mls

@@ -0,0 +1,29 @@
+:js
+
+:expect 4
+fun f(y) =
+  let x = 0
+  class A() with
+    fun g() =
+      set x += 1
+      set y += 1
+  fun h() =
+    set x += 1
+    set y += 1
+  A().g()
+  h()
+  x + y
+f(0)
+//│ = 4
+
+:expect 0
+fun f() =
+  let x = 0
+  class A() with
+    let x = 2
+    fun g() =
+      set x += 1
+  A().g()
+  x
+f()
+//│ = 0

hkmc2/shared/src/test/mlscript/codegen/While.mls

@@ -197,14 +197,14 @@ fun f(ls) =
   else log("Done!")
 //│ JS:
 //│ function f(ls) {
-//│   let ls1, param0, param1, h, tl, tmp;
+//│   let param0, param1, h, tl, tmp;
 //│   tmp1: while (true) {
-//│     if (ls1 instanceof globalThis.Cons.class) {
-//│       param0 = ls1.hd;
-//│       param1 = ls1.tl;
+//│     if (ls instanceof globalThis.Cons.class) {
+//│       param0 = ls.hd;
+//│       param1 = ls.tl;
 //│       h = param0;
 //│       tl = param1;
-//│       ls1 = tl;
+//│       ls = tl;
 //│       tmp = globalThis.log(h);
 //│       continue tmp1;
 //│     } else {
@@ -220,9 +220,13 @@ f(0)
 //│ > Done!
 
 f(Cons(1, 0))
+//│ > 1
 //│ > Done!
 
 f(Cons(1, Cons(2, Cons(3, 0))))
+//│ > 1
+//│ > 2
+//│ > 3
 //│ > Done!
 
 
@@ -239,7 +243,7 @@ while log("Hello World"); false
   then 0(0)
   else 1
 //│ ╔══[PARSE ERROR] Unexpected 'then' keyword here
-//│ ║  l.239: 	  then 0(0)
+//│ ║  l.243: 	  then 0(0)
 //│ ╙──       	  ^^^^
 //│ ═══[ERROR] Unrecognized term split (false literal).
 //│ ═══[RUNTIME ERROR] Error: match error