fix immutability for ARC4 struct and address types

examples/amm/out_unoptimized/ConstantProductAMM.approval.teal

@@ -588,10 +588,14 @@ do_asset_transfer:
     //     asset_receiver=receiver,
     // ).submit()
     itxn_begin
-    // amm/contract.py:357
-    // def do_asset_transfer(*, receiver: Account, asset: Asset, amount: UInt64) -> None:
+    // amm/contract.py:359
+    // xfer_asset=asset,
     frame_dig -2
+    // amm/contract.py:360
+    // asset_amount=amount,
     frame_dig -1
+    // amm/contract.py:361
+    // asset_receiver=receiver,
     frame_dig -3
     itxn_field AssetReceiver
     itxn_field AssetAmount

examples/auction/out_unoptimized/Auction.approval.teal

@@ -270,8 +270,8 @@ opt_into_asset:
     // auction/contract.py:36
     // asset_receiver=Global.current_application_address,
     global CurrentApplicationAddress
-    // auction/contract.py:26
-    // def opt_into_asset(self, asset: Asset) -> None:
+    // auction/contract.py:37
+    // xfer_asset=asset,
     frame_dig -1
     itxn_field XferAsset
     itxn_field AssetReceiver
@@ -525,8 +525,8 @@ claim_asset:
     //     asset_amount=self.asa_amount,
     // ).submit()
     itxn_begin
-    // auction/contract.py:98
-    // def claim_asset(self, asset: Asset) -> None:
+    // auction/contract.py:102
+    // xfer_asset=asset,
     frame_dig -1
     // auction/contract.py:103
     // asset_close_to=self.previous_bidder,

examples/sizes.txt

@@ -6,20 +6,21 @@
  application/Reference                          177     167       -    |         92      83       - 
  arc4_dynamic_arrays/DynamicArray              2695    1931       -    |       1733    1138       - 
  arc4_numeric_comparisons/UIntNOrdering        1100     908       -    |        786     597       - 
- arc4_types/Arc4Address                          85      62       -    |         37      18       - 
+ arc4_types/Arc4Address                          79      18       -    |         34      11       - 
  arc4_types/Arc4Arrays                          623     376       -    |        368     182       - 
  arc4_types/Arc4BoolEval                        751      14       -    |        167       8       - 
  arc4_types/Arc4BoolType                        381      69       -    |        307      46       - 
  arc4_types/Arc4DynamicBytes                    377     185       -    |        213     100       - 
  arc4_types/Arc4DynamicStringArray              283     124       -    |        172      53       - 
- arc4_types/Arc4MutableParams                   471     286       -    |        292     141       - 
+ arc4_types/Arc4MutableParams                  1110     644       -    |        699     343       - 
  arc4_types/Arc4Mutation                       2958    1426       -    |       1977     593       - 
  arc4_types/Arc4NumericTypes                    749     186       -    |        243      26       - 
  arc4_types/Arc4RefTypes                         85      46       -    |         32      27       - 
  arc4_types/Arc4StringTypes                     455      35       -    |        245      13       - 
  arc4_types/Arc4StructsFromAnotherModule         67      12       -    |         49       6       - 
- arc4_types/Arc4StructsType                     302     239       -    |        204     121       - 
+ arc4_types/Arc4StructsType                     389     239       -    |        259     121       - 
  arc4_types/Arc4TuplesType                      795     136       -    |        537      58       - 
+ arc4_types/MutableParams2                      334     202       -    |        193      97       - 
  arc_28/EventEmitter                            186     133       -    |        100      64       - 
  asset/Reference                                268     261       -    |        144     141       - 
  auction/Auction                                592     522       -    |        328     281       - 
@@ -108,7 +109,7 @@
  state_totals                                    65      32       -    |         32      16       - 
  stress_tests/BruteForceRotationSearch          228     163       -    |        152     106       - 
  string_ops                                     156     154       -    |         58      55       - 
- struct_in_box/Example                          243     206       -    |        127      99       - 
+ struct_in_box/Example                          242     206       -    |        127      99       - 
  stubs/BigUInt                                  192     121       -    |        126      73       - 
  stubs/Bytes                                    944     279       -    |        606     153       - 
  stubs/String                                   701     167       -    |        416      54       - 
@@ -128,6 +129,6 @@
  unassigned_expression/Unassigned               158     119       -    |         81      57       - 
  undefined_phi_args/Baddie                      319     282       -    |        174     157       - 
  unssa/UnSSA                                    432     368       -    |        241     204       - 
- voting/VotingRoundApp                         1593    1483       -    |        734     649       - 
+ voting/VotingRoundApp                         1590    1483       -    |        733     649       - 
  with_reentrancy/WithReentrancy                 255     242       -    |        132     122       - 
- Total                                        69200   53576   53517    |      32843   21764   21720 
+ Total                                        70250   54092   54033    |      33494   22056   22012 

examples/struct_in_box/out_unoptimized/ExampleContract.approval.teal

@@ -165,9 +165,10 @@ write_to_box:
     // @subroutine
     // def write_to_box(self, user: UserStruct) -> None:
     proto 1 1
+    frame_dig -1
     // struct_in_box/contract.py:20
     // box_key = user.id.bytes
-    frame_dig -1
+    dup
     intc_2 // 2
     intc_3 // 8
     extract3 // on error: Index access is out of bounds
@@ -181,7 +182,6 @@ write_to_box:
     // op.Box.put(box_key, user.bytes)
     frame_dig -1
     box_put
-    frame_dig -1
     retsub
 
 

examples/voting/out_unoptimized/VotingRoundApp.approval.teal

@@ -281,9 +281,10 @@ store_option_counts:
     // @subroutine
     // def store_option_counts(self, option_counts: VoteIndexArray) -> None:
     proto 1 1
+    frame_dig -1
     // voting/voting.py:219
     // assert option_counts.length, "option_counts should be non-empty"
-    frame_dig -1
+    dup
     intc_0 // 0
     extract_uint16
     intc_0 // 0
@@ -310,33 +311,33 @@ store_option_counts:
 store_option_counts_for_header@1:
     // voting/voting.py:223
     // for item in option_counts:
+    frame_dig 3
     frame_dig 2
-    frame_dig 1
     <
     bz store_option_counts_after_for@4
     frame_dig -1
     extract 2 0
-    frame_dig 2
+    frame_dig 3
     intc_1 // 1
     *
     intc_1 // 1
     extract3 // on error: Index access is out of bounds
     // voting/voting.py:224
     // total_options += item.native
     btoi
-    frame_dig 0
+    frame_dig 1
     +
-    frame_bury 0
-    frame_dig 2
+    frame_bury 1
+    frame_dig 3
     intc_1 // 1
     +
-    frame_bury 2
+    frame_bury 3
     b store_option_counts_for_header@1
 
 store_option_counts_after_for@4:
     // voting/voting.py:225
     // assert total_options <= 128, "Can't have more than 128 vote options"
-    frame_dig 0
+    frame_dig 1
     dup
     pushint 128 // 128
     <=
@@ -352,8 +353,6 @@ store_option_counts_after_for@4:
     bytec 14 // "total_options"
     swap
     app_global_put
-    frame_dig -1
-    frame_bury 0
     retsub
 
 
@@ -808,8 +807,8 @@ close_after_for@14:
     bytec 13 // "nft_image_url"
     app_global_get_ex
     assert // check self.nft_image_url exists
-    // voting/voting.py:144
-    // note += "]}}"
+    // voting/voting.py:153
+    // note=note,
     uncover 2
     itxn_field Note
     itxn_field ConfigAssetURL

src/puya/awst/nodes.py

@@ -1337,11 +1337,15 @@ def accept(self, visitor: StatementVisitor[T]) -> T:
 @attrs.frozen
 class BytesAugmentedAssignment(Statement):
     target: Lvalue = attrs.field(
-        validator=[expression_has_wtype(wtypes.bytes_wtype, wtypes.string_wtype)]
+        validator=[
+            expression_has_wtype(wtypes.bytes_wtype, wtypes.string_wtype, wtypes.arc4_string_alias)
+        ]
     )
     op: BytesBinaryOperator
     value: Expression = attrs.field(
-        validator=[expression_has_wtype(wtypes.bytes_wtype, wtypes.string_wtype)]
+        validator=[
+            expression_has_wtype(wtypes.bytes_wtype, wtypes.string_wtype, wtypes.arc4_string_alias)
+        ]
     )
 
     @value.validator

src/puya/awst/validation/arc4_copy.py

@@ -44,27 +44,53 @@ def visit_tuple_expression(self, expr: awst_nodes.TupleExpression) -> None:
                 _check_for_arc4_copy(item, "being passed to a tuple expression")
 
     def visit_for_in_loop(self, statement: awst_nodes.ForInLoop) -> None:
+        # statement.items is immediately checked before entering the for body
+        # so don't need to worry about preserving _for_items through multiple loops
         self._for_items = statement.items
         super().visit_for_in_loop(statement)
         self._for_items = None
 
+        # looping is essentially assigning so check sequence
+        sequence = statement.sequence
+        while isinstance(sequence, awst_nodes.Enumeration | awst_nodes.Reversed):
+            sequence = sequence.expr
+        if (  # mutable tuples cannot be iterated in a semantically correct way
+            isinstance(sequence.wtype, wtypes.WTuple)
+            and _is_referable_expression(sequence)
+            and _is_arc4_mutable(sequence.wtype)
+        ):
+            logger.error(
+                "tuple of mutable ARC4 values cannot be iterated",
+                location=sequence.source_location,
+            )
+        elif (  # arrays of mutable types, must be modified and iterated by index
+            isinstance(sequence.wtype, wtypes.ARC4Array)
+            and _is_referable_expression(sequence)
+            and _is_arc4_mutable(sequence.wtype.element_type)
+        ):
+            logger.error(
+                "cannot directly iterate an ARC4 array of mutable objects,"
+                " construct a for-loop over the indexes instead",
+                location=sequence.source_location,
+            )
+
     def visit_assignment_expression(self, expr: awst_nodes.AssignmentExpression) -> None:
         _check_assignment(expr.target, expr.value)
         expr.value.accept(self)
 
     def visit_subroutine_call_expression(self, expr: awst_nodes.SubroutineCallExpression) -> None:
-        super().visit_subroutine_call_expression(expr)
-        for arg in expr.args:
-            match arg.value:
-                case awst_nodes.VarExpression():
-                    # Var expressions don't need copy as we implicitly return the latest value and
-                    # update the var
-                    continue
-                case awst_nodes.AppStateExpression() | awst_nodes.AppAccountStateExpression():
-                    message = "being passed to a subroutine from state"
-                case _:
-                    message = "being passed to a subroutine"
-            _check_for_arc4_copy(arg.value, message)
+        for arg_ in expr.args:
+            for arg in _expand_tuple_items(arg_.value):
+                match arg:
+                    case awst_nodes.VarExpression():
+                        # Var expressions don't need copy as we implicitly return the latest value
+                        # and update the var
+                        continue
+                    case awst_nodes.AppStateExpression() | awst_nodes.AppAccountStateExpression():
+                        message = "being passed to a subroutine from state"
+                    case _:
+                        message = "being passed to a subroutine"
+                _check_for_arc4_copy(arg, message)
 
     def visit_new_array(self, expr: awst_nodes.NewArray) -> None:
         super().visit_new_array(expr)
@@ -131,7 +157,8 @@ def _check_for_arc4_copy(expr: awst_nodes.Expression, context_desc: str) -> None
 def _expand_tuple_items(expr: awst_nodes.Expression) -> Iterator[awst_nodes.Expression]:
     match expr:
         case awst_nodes.TupleExpression(items=items):
-            yield from items
+            for item in items:
+                yield from _expand_tuple_items(item)
         case _:
             yield expr