docs: Aztec smart contract tutorial - crowdfunding (#5786)

A tutorial to teach some of the fundamentals of building smart contracts
on Aztec.

---------

Co-authored-by: josh crites <critesjosh@gmail.com>

docs/docs/developers/contracts/writing_contracts/functions/initializers.md

@@ -10,8 +10,7 @@ Initializers are regular functions that set an "initialized" flag (a nullifier)
 
 ## Annotate with `#[aztec(private)]` and `#[aztec(initializer)]`
 
-
-Define your initiaizer like so:
+Define your initializer like so:
 
 ```rust
 #[aztec(private)]

docs/docs/developers/tutorials/crowdfunding/donations.md

@@ -0,0 +1,216 @@
+---
+title: Build a donations contract
+tags: [developers, tutorial, example]
+---
+
+# Build a donations contract
+
+In this tutorial we'll create two contracts related to crowdfunding:
+
+- A crowdfunding contract with two core components
+  - Fully private donations
+  - Verifiable withdrawals to the operator
+- A reward contract for anyone else to anonymously reward donors
+
+Along the way you will:
+
+- Install Aztec developer tools
+- Setup a new Noir contract project
+- Add base Aztec dependencies
+- Call between private and public contexts
+- Wrap an address with its interface (token)
+- Create custom private value notes
+
+## Setup
+
+### Install tools
+
+Please ensure that the you already have [Installed the Sandbox](https://docs.aztec.network/developers/getting_started/quickstart#install-the-sandbox).
+
+And if using VSCode, see [here](https://docs.aztec.network/developers/contracts/main#install-noir-lsp-recommended) to install Noir LSP, where you'll benefit from syntax highlighting, profiling, and more.
+
+### Create an Aztec project
+
+Use `aztec-nargo` in a terminal to create a new Aztec contract project named "crowdfunding":
+
+```sh
+aztec-nargo new --contract crowdfunding
+```
+
+Inside the new `crowdfunding` directory you will have a base to implement the Aztec smart contract.
+
+Use `aztec-nargo --help` to see other commands.
+
+## Private donations
+
+1. An "Operator" begins a Crowdfunding campaign (contract), specifying:
+
+- an existing token address
+- their account address
+- a deadline timestamp
+
+2. Any address can donate (in private context)
+
+- private transfer token from sender to contract
+- transaction receipts allow private claims via another contract
+
+3. Only the operator can withdraw from the fund
+
+### 1. Create a campaign
+
+#### Initialize
+
+Open the project in your preferred editor. If using VSCode and the LSP, you'll be able to select the `aztec-nargo` binary to use (instead of `nargo`).
+
+In `main.nr`, rename the contract from `Main`, to `Crowdfunding`.
+
+#include_code empty-contract /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+Replace the example functions with an initializer that takes the required campaign info as parameters. Notice use of `#[aztec(...)]` macros inform the compiler that the function is a public initializer.
+
+```rust
+#include_code init-header /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr raw
+  //...
+}
+```
+
+More about initializers [here](../../contracts/writing_contracts/functions/initializers.md).
+
+#### Dependencies
+
+When you compile the contracts by running `aztec-nargo compile` in your project directory, you'll notice it cannot resolve `AztecAddress`. (Or hovering over in VSCode)
+
+```rust
+#include_code init-header-error /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr raw
+  //...
+}
+```
+
+Add the required dependency by going to your project's `Nargo.toml` file, and adding `aztec` from the `aztec-nr` framework. It resides in the `aztec-packages` mono-repo:
+
+```rust
+[dependencies]
+aztec = { git="https://github.com/AztecProtocol/aztec-packages/", tag="#include_aztec_version", directory="noir-projects/aztec-nr/aztec" }
+```
+
+A word about versions:
+- Choose the aztec packages version to match your aztec tools as seen here - `aztec-cli -V`
+- Check that your `compiler_version` in Nargo.toml is satisified by your aztec compiler - `aztec-nargo -V`
+
+More about versions [here](https://docs.aztec.network/developers/versions-updating).
+
+Inside the Crowdfunding contract definition, use the dependency that defines the address type `AztecAddress` (same syntax as Rust)
+
+```rust
+use dep::aztec::protocol_types::address::AztecAddress;
+```
+
+The `aztec::protocol_types` can be browsed [here](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/noir-projects/noir-protocol-circuits/crates/types/src). And like rust dependencies, the relative path inside the dependency corresponds to `address::AztecAddress`.
+
+
+#### Storage
+
+To retain the initializer parameters in the contract's Storage, we'll need to declare them in a preceding `Storage` struct:
+
+#include_code storage /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+The `ValueNote` type is in the top-level of the Aztec.nr framework, namely [noir-projects/aztec-nr](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/noir-projects/aztec-nr/value-note/src/value_note.nr). Like before, you'll need to add the crate to Nargo.toml
+
+(See [here](https://docs.aztec.network/developers/contracts/resources/dependencies) for common dependencies).
+
+---
+
+Back in main.nr, reference `use` of the type
+
+```rust
+use dep::value_note::value_note::ValueNote;
+```
+
+Now complete the initializer by setting the storage variables with the parameters:
+
+#include_code init /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+You can compile the code so far with `aztec-nargo compile`.
+
+### 2. Taking private donations
+
+#### Checking campaign duration against the timestamp
+
+To check that the donation occurs before the campaign deadline, we must access the public `timestamp`. It is one of several [Public Global Variables](https://docs.aztec.network/developers/contracts/references/globals#public-global-variables).
+
+Declare an Aztec function that is public and internal
+
+```rust
+#include_code deadline-header /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr raw
+    //...
+}
+```
+
+Read the deadline from storage and assert that the `timestamp` from this context is before the deadline
+
+#include_code deadline /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+---
+
+Since donations are to be private, the donate function will have the user's private context which has these [Private Global Variables](https://docs.aztec.network/developers/contracts/references/globals#private-global-variables). So from the private context there is a little extra to call the (public internal) `_check_deadline` function.
+
+```rust
+#include_code call-check-deadline /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr raw
+  //...
+}
+```
+
+Namely calling `enqueue` and passing the (mutable) context.
+
+Now conclude adding all dependencies to the `Crowdfunding` contract:
+
+#include_code all-deps /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+Like before, you can find these and other `aztec::protocol_types` [here](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/noir-projects/noir-protocol-circuits/crates/types/src).
+
+
+#### Interfacing with another contract
+
+The token being used for donations is stored simply as an `AztecAddress` (named `donation_token`). so to easily use it as a token, we let the compiler know that we want the address to have a Token interface. Here we will use a maintained example Token contract.
+
+Add this `Token` contract to Nargo.toml:
+
+```
+token = { git="https://github.com/AztecProtocol/aztec-packages/", tag="#include_aztec_version", directory="noir-projects/noir-contracts/contracts/token_contract" }
+```
+
+With the dependency already `use`d at the start of the contract, the token contract can be called to make the transfer from msg sender to this contract. 
+
+:::note
+The user must have authorised this action (concept [here](../../../learn/concepts/accounts/main#authorizing-actions)), example use of `createAuthWit` in 'full donor flow' test [here](../../../../../yarn-project/end-to-end/src/e2e_crowdfunding_and_claim.test.ts).
+:::
+
+#### Creating and storing a private receipt note
+
+The last thing to do is create a new value note and add it to the `donation_receipts`. So the full donation function is now
+
+#include_code donate /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+### 3. Operator withdrawals
+
+The remaining function to implement, `withdraw`, is reasonably straight-forward:
+1. make sure the address calling is the operator address
+2. transfer tokens from the contract to the operator
+3. reveal that an amount has been withdrawn to the operator
+
+The last point is achieved by emitting an unencrypted event log, more [here](https://docs.aztec.network/developers/contracts/writing_contracts/events/emit_event#unencrypted-events).
+
+Copy the last function into your Crowdfunding contract:
+
+#include_code operator-withdrawals /noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr rust
+
+You should be able to compile successfully with `aztec-nargo compile`.
+
+## Conclusion
+
+For comparison, the full Crowdfunding contract can be found [here](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/noir-projects/noir-contracts/contracts/crowdfunding_contract).
+
+### Next steps?
+
+If a new token wishes to honour donors with free tokens based on donation amounts, this is possible via the donation_receipts (a `PrivateSet`).
+See [claim_contract](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/noir-projects/noir-contracts/contracts/claim_contract).

docs/sidebars.js

@@ -228,7 +228,7 @@ const sidebars = {
       items: [
         "developers/tutorials/writing_token_contract",
         "developers/tutorials/writing_private_voting_contract",
-
+        "developers/tutorials/crowdfunding/donations",
         {
           label: "Writing a DApp",
           type: "category",

noir-projects/noir-contracts/contracts/crowdfunding_contract/src/main.nr

@@ -1,11 +1,15 @@
+// docs:start:empty-contract
 contract Crowdfunding {
+    // docs:end:empty-contract
 
+    // docs:start:all-deps
     use dep::aztec::{
         protocol_types::{abis::function_selector::FunctionSelector, address::AztecAddress, traits::Serialize},
         state_vars::{PrivateSet, PublicImmutable, SharedImmutable}
     };
     use dep::value_note::value_note::ValueNote;
     use dep::token::Token;
+    // docs:end:all-deps
 
     #[aztec(event)]
     struct WithdrawalProcessed {
@@ -19,6 +23,7 @@ contract Crowdfunding {
         }
     }
 
+    // docs:start:storage
     #[aztec(storage)]
     struct Storage {
         // Token used for donations (e.g. DAI)
@@ -27,44 +32,63 @@ contract Crowdfunding {
         operator: SharedImmutable<AztecAddress>,
         // End of the crowdfunding campaign after which no more donations are accepted
         deadline: PublicImmutable<u64>,
-        // Notes emitted to donors when they donate (later on used to claim rewards in the Claim contract)
-        claim_notes: PrivateSet<ValueNote>,
+        // Notes emitted to donors when they donate (can be used as proof to obtain rewards, eg in Claim contracts)
+        donation_receipts: PrivateSet<ValueNote>,
     }
+    // docs:end:storage
 
+    // docs:start:init
+    // docs:start:init-header
+    // docs:start:init-header-error
     #[aztec(public)]
     #[aztec(initializer)]
-    fn constructor(donation_token: AztecAddress, operator: AztecAddress, deadline: u64) {
+    // this-will-error:init-header-error
+    fn init(donation_token: AztecAddress, operator: AztecAddress, deadline: u64) {
+        // docs:end:init-header
+        // docs:end:init-header-error
         storage.donation_token.initialize(donation_token);
         storage.operator.initialize(operator);
         storage.deadline.initialize(deadline);
     }
+    // docs:end:init
 
+    // docs:start:deadline
+    // docs:start:deadline-header
     #[aztec(public)]
     #[aztec(internal)]
     fn _check_deadline() {
+        // docs:end:deadline-header
         let deadline = storage.deadline.read();
         assert(context.timestamp() < deadline, "Deadline has passed");
     }
+    // docs:end:deadline
 
+    // docs:start:donate
+    // docs:start:call-check-deadline
     #[aztec(private)]
     fn donate(amount: u64) {
         // 1) Check that the deadline has not passed
         Crowdfunding::at(context.this_address())._check_deadline().enqueue(&mut context);
+        // docs:end:call-check-deadline
 
+        // docs:start:do-transfer
         // 2) Transfer the donation tokens from donor to this contract
         Token::at(storage.donation_token.read_private()).transfer(
             context.msg_sender(),
             context.this_address(),
             amount as Field,
             0
         ).call(&mut context);
+        // docs:end:do-transfer
 
         // 3) Create a value note for the donor so that he can later on claim a rewards token in the Claim
         // contract by proving that the hash of this note exists in the note hash tree.
         let mut note = ValueNote::new(amount as Field, context.msg_sender());
-        storage.claim_notes.insert(&mut note, true);
+        storage.donation_receipts.insert(&mut note, true);
     }
+    // docs:end:donate
 
+    // docs:start:operator-withdrawals
     // Withdraws balance to the operator. Requires that msg_sender() is the operator.
     #[aztec(private)]
     fn withdraw(amount: u64) {
@@ -79,4 +103,5 @@ contract Crowdfunding {
         let event = WithdrawalProcessed { amount, who: operator_address };
         context.emit_unencrypted_log(event.serialize());
     }
+    // docs:end:operator-withdrawals
 }