Document new ABI features

.flake8

@@ -10,6 +10,7 @@ ignore =
 
 per-file-ignores =
     pyteal/compiler/optimizer/__init__.py:          F401
+    examples/application/abi/algobank.py:           F403, F405
     examples/application/asset.py:                  F403, F405
     examples/application/opup.py:                   F403, F405
     examples/application/security_token.py:         F403, F405

docs/api.rst

@@ -24,3 +24,19 @@ PyTeal Package
       :annotation: = <pyteal.TxnObject object>
 
       The most recently submitted inner transaction. This is an instance of :any:`TxnObject`.
+
+      If a transaction group was submitted most recently, then this will be the last transaction in that group.
+
+   .. data:: Gitxn
+      :annotation: = <pyteal.InnerTxnGroup object>
+
+      The most recently submitted inner transaction group. This is an instance of :any:`InnerTxnGroup`.
+
+      If a single transaction was submitted most recently, then this will be a group of size 1.
+
+.. automodule:: pyteal.abi
+   :members:
+   :undoc-members:
+   :imported-members:
+   :special-members: __getitem__
+   :show-inheritance:

docs/index.rst

@@ -45,6 +45,7 @@ PyTeal **hasn't been security audited**. Use it at your own risk.
    versions
    compiler_optimization
    opup
+   abi
 
 .. toctree::
    :maxdepth: 3

docs/versions.rst

@@ -1,6 +1,6 @@
 .. _versions:
 
-TEAL Versions
+Versions
 =============
 
 Each version of PyTeal compiles contracts for a specific version of TEAL. Newer versions of TEAL
@@ -18,14 +18,34 @@ TEAL Version PyTeal Version
 6            >= 0.10.0
 ============ ==============
 
+.. _version pragmas:
+
+Version Pragmas
+----------------
+
+When writing a PyTeal smart contract, it's important to target a specific AVM version and to compile
+with a single PyTeal version. This will ensure your compiled program remains consistent and has the
+exact same behavior no matter when you compile it.
+
+The :any:`pragma` function can be used to assert that the current PyTeal version matches a constraint
+of your choosing. This can help strengthen the dependency your source code has on the PyTeal package
+version you used when writing it.
+
+If you are writing code for others to consume, or if your codebase has different PyTeal version
+dependencies in different places, the :any:`Pragma` expression can be used to apply a pragma
+constraint to only a section of the AST.
+
+PyTeal v0.5.4 and Below
+-----------------------
+
 In order to support TEAL v2, PyTeal v0.6.0 breaks backward compatibility with v0.5.4. PyTeal
 programs written for PyTeal version 0.5.4 and below will not compile properly and most likely will
 display an error of the form :code:`AttributeError: * object has no attribute 'teal'`.
 
-**WARNING:** before updating PyTeal to a version with generates TEAL v2 contracts and fixing the
-programs to use the global function :any:`compileTeal` rather the class method :code:`.teal()`, make
-sure your program abides by the TEAL safety guidelines `<https://developer.algorand.org/docs/reference/teal/guidelines/>`_.
-Changing a v1 TEAL program to a v2 TEAL program without any code changes is insecure because v2
-TEAL programs allow rekeying. Specifically, you must add a check that the :code:`RekeyTo` property
-of any transaction is set to the zero address when updating an older PyTeal program from v0.5.4 and
-below.
+.. warning::
+    If you are updating from a v1 TEAL program, make
+    sure your program abides by the `TEAL safety guidelines <https://developer.algorand.org/docs/reference/teal/guidelines/>`_.
+    Changing a v1 TEAL program to a v2 TEAL program without any code changes is insecure because v2
+    TEAL programs allow rekeying. Specifically, you must add a check that the :code:`RekeyTo` property
+    of any transaction is set to the zero address when updating an older PyTeal program from v0.5.4 and
+    below.

examples/application/abi/algobank.json

@@ -0,0 +1,54 @@
+{
+    "name": "AlgoBank",
+    "methods": [
+        {
+            "name": "deposit",
+            "args": [
+                {
+                    "type": "pay",
+                    "name": "payment"
+                },
+                {
+                    "type": "account",
+                    "name": "sender"
+                }
+            ],
+            "returns": {
+                "type": "void"
+            },
+            "desc": "This method receives a payment from an account opted into this app and records it in their local state. The caller may opt into this app during this call."
+        },
+        {
+            "name": "getBalance",
+            "args": [
+                {
+                    "type": "account",
+                    "name": "user"
+                }
+            ],
+            "returns": {
+                "type": "uint64"
+            },
+            "desc": "Lookup the balance of a user held by this app."
+        },
+        {
+            "name": "withdraw",
+            "args": [
+                {
+                    "type": "uint64",
+                    "name": "amount"
+                },
+                {
+                    "type": "account",
+                    "name": "recipient"
+                }
+            ],
+            "returns": {
+                "type": "void"
+            },
+            "desc": "Withdraw an amount of Algos held by this app. The sender of this method call will be the source of the Algos, and the destination will be the `recipient` argument. This may or may not be the same as the sender's address. This method will fail if the amount of Algos requested to be withdrawn exceeds the amount of Algos held by this app for the sender. The Algos will be transferred to the recipient using an inner transaction whose fee is set to 0, meaning the caller's transaction must include a surplus fee to cover the inner transaction."
+        }
+    ],
+    "desc": null,
+    "networks": {}
+}

examples/application/abi/algobank.py

@@ -0,0 +1,113 @@
+# This example is provided for informational purposes only and has not been audited for security.
+from pyteal import *
+import json
+
+
+@Subroutine(TealType.none)
+def assert_sender_is_creator() -> Expr:
+    return Assert(Txn.sender() == Global.creator_address())
+
+
+# move any balance that the user has into the "lost" amount when they close out or clear state
+transfer_balance_to_lost = App.globalPut(
+    Bytes("lost"),
+    App.globalGet(Bytes("lost")) + App.localGet(Txn.sender(), Bytes("balance")),
+)
+
+router = Router(
+    name="AlgoBank",
+    bare_calls=BareCallActions(
+        # approve a creation no-op call
+        no_op=OnCompleteAction(action=Approve(), call_config=CallConfig.CREATE),
+        # approve opt-in calls during normal usage, and during creation as a convenience for the creator
+        opt_in=OnCompleteAction(action=Approve(), call_config=CallConfig.ALL),
+        # move any balance that the user has into the "lost" amount when they close out or clear state
+        close_out=OnCompleteAction(
+            action=transfer_balance_to_lost, call_config=CallConfig.CALL
+        ),
+        clear_state=OnCompleteAction(
+            action=transfer_balance_to_lost, call_config=CallConfig.CALL
+        ),
+        # only the creator can update or delete the app
+        update_application=OnCompleteAction(
+            action=assert_sender_is_creator, call_config=CallConfig.CALL
+        ),
+        delete_application=OnCompleteAction(
+            action=assert_sender_is_creator, call_config=CallConfig.CALL
+        ),
+    ),
+)
+
+
+@router.method(no_op=CallConfig.CALL, opt_in=CallConfig.CALL)
+def deposit(payment: abi.PaymentTransaction, sender: abi.Account) -> Expr:
+    """This method receives a payment from an account opted into this app and records it in
+    their local state.
+
+    The caller may opt into this app during this call.
+    """
+    return Seq(
+        Assert(payment.get().sender() == sender.address()),
+        Assert(payment.get().receiver() == Global.current_application_address()),
+        App.localPut(
+            sender.address(),
+            Bytes("balance"),
+            App.localGet(sender.address(), Bytes("balance")) + payment.get().amount(),
+        ),
+    )
+
+
+@router.method
+def getBalance(user: abi.Account, *, output: abi.Uint64) -> Expr:
+    """Lookup the balance of a user held by this app."""
+    return output.set(App.localGet(user.address(), Bytes("balance")))
+
+
+@router.method
+def withdraw(amount: abi.Uint64, recipient: abi.Account) -> Expr:
+    """Withdraw an amount of Algos held by this app.
+
+    The sender of this method call will be the source of the Algos, and the destination will be
+    the `recipient` argument. This may or may not be the same as the sender's address.
+
+    This method will fail if the amount of Algos requested to be withdrawn exceeds the amount of
+    Algos held by this app for the sender.
+
+    The Algos will be transferred to the recipient using an inner transaction whose fee is set
+    to 0, meaning the caller's transaction must include a surplus fee to cover the inner
+    transaction.
+    """
+    return Seq(
+        # if amount is larger than App.localGet(Txn.sender(), Bytes("balance")), the subtraction
+        # will underflow and fail this method call
+        App.localPut(
+            Txn.sender(),
+            Bytes("balance"),
+            App.localGet(Txn.sender(), Bytes("balance")) - amount.get(),
+        ),
+        InnerTxnBuilder.Begin(),
+        InnerTxnBuilder.SetFields(
+            {
+                TxnField.type_enum: TxnType.Payment,
+                TxnField.receiver: recipient.address(),
+                TxnField.amount: amount.get(),
+                TxnField.fee: Int(0),
+            }
+        ),
+        InnerTxnBuilder.Submit(),
+    )
+
+
+approval_program, clear_state_program, contract = router.compile_program(
+    version=6, optimize=OptimizeOptions(scratch_slots=True)
+)
+
+if __name__ == "__main__":
+    with open("algobank_approval.teal", "w") as f:
+        f.write(approval_program)
+
+    with open("algobank_clear_state.teal", "w") as f:
+        f.write(clear_state_program)
+
+    with open("algobank.json", "w") as f:
+        f.write(json.dumps(contract.dictify(), indent=4))