docs: document stable public state usage (AztecProtocol#4324)

Fixes AztecProtocol#4325

Author: LHerskind

docs/docs/developers/contracts/syntax/storage/public_state.md

@@ -90,3 +90,45 @@ We have a `write` method on the `PublicState` struct that takes the value to wri
 #### Writing to our `minters` example
 
 #include_code write_minter /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust
+
+---
+
+## Stable Public State
+
+`StablePublicState` is a special type of `PublicState` that can be read from both public and private! 
+
+Since private execution is based on historical data, the user can pick ANY of its prior values to read from. This is why it `MUST` not be updated after the contract is deployed. The variable should be initialized at the constructor and then never changed. 
+
+This makes the stable public variables useful for stuff that you would usually have in `immutable` values in solidity. For example this can be the name of a token or its number of decimals.
+
+Just like the `PublicState` it is generic over the variable type `T`. The type `MUST` implement Serialize and Deserialize traits.
+
+You can find the details of `StablePublicState` in the implementation [here](https://github.com/AztecProtocol/aztec-packages/blob/#include_aztec_version/yarn-project/aztec-nr/aztec/src/state_vars/stable_public_state.nr).
+
+### `new`
+Is done exactly like the `PublicState` struct, but with the `StablePublicState` struct.
+
+#include_code storage_decimals /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust
+
+#include_code storage_decimals_init /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust
+
+### `initialize`
+
+#include_code initialize_decimals /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust
+
+:::warning Should only be called as part of the deployment.
+If this is called outside the deployment transaction multiple values could be used down the line, potentially breaking the contract.
+
+Currently this is not constrained as we are in the middle of changing deployments.
+:::
+
+### `read_public`
+
+Reading the value is like `PublicState`, simply with `read_public` instead of `read`.
+#include_code read_decimals_public /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust
+
+
+### `read_private`
+Reading the value is like `PublicState`, simply with `read_private` instead of `read`. This part can only be executed in private.
+
+#include_code read_decimals_private /yarn-project/noir-contracts/contracts/token_contract/src/main.nr rust

yarn-project/end-to-end/src/e2e_token_contract.test.ts

@@ -87,43 +87,87 @@ describe('e2e_token_contract', () => {
       reader = await ReaderContract.deploy(wallets[0]).send().deployed();
     });
 
-    it('name', async () => {
-      const t = toString(await asset.methods.un_get_name().view());
-      expect(t).toBe(TOKEN_NAME);
+    describe('name', () => {
+      it('private', async () => {
+        const t = toString(await asset.methods.un_get_name().view());
+        expect(t).toBe(TOKEN_NAME);
 
-      const tx = reader.methods.check_name(asset.address, TOKEN_NAME).send();
-      const receipt = await tx.wait();
-      expect(receipt.status).toBe(TxStatus.MINED);
+        const tx = reader.methods.check_name_private(asset.address, TOKEN_NAME).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
+
+        await expect(reader.methods.check_name_private(asset.address, 'WRONG_NAME').simulate()).rejects.toThrowError(
+          "Cannot satisfy constraint 'name.is_eq(_what)'",
+        );
+      });
+
+      it('public', async () => {
+        const t = toString(await asset.methods.un_get_name().view());
+        expect(t).toBe(TOKEN_NAME);
 
-      await expect(reader.methods.check_name(asset.address, 'WRONG_NAME').simulate()).rejects.toThrowError(
-        "Failed to solve brillig function, reason: explicit trap hit in brillig 'name.is_eq(_what)'",
-      );
+        const tx = reader.methods.check_name_public(asset.address, TOKEN_NAME).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
+
+        await expect(reader.methods.check_name_public(asset.address, 'WRONG_NAME').simulate()).rejects.toThrowError(
+          "Failed to solve brillig function, reason: explicit trap hit in brillig 'name.is_eq(_what)'",
+        );
+      });
     });
 
-    it('symbol', async () => {
-      const t = toString(await asset.methods.un_get_symbol().view());
-      expect(t).toBe(TOKEN_SYMBOL);
+    describe('symbol', () => {
+      it('private', async () => {
+        const t = toString(await asset.methods.un_get_symbol().view());
+        expect(t).toBe(TOKEN_SYMBOL);
 
-      const tx = reader.methods.check_symbol(asset.address, TOKEN_SYMBOL).send();
-      const receipt = await tx.wait();
-      expect(receipt.status).toBe(TxStatus.MINED);
+        const tx = reader.methods.check_symbol_private(asset.address, TOKEN_SYMBOL).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
+
+        await expect(
+          reader.methods.check_symbol_private(asset.address, 'WRONG_SYMBOL').simulate(),
+        ).rejects.toThrowError("Cannot satisfy constraint 'symbol.is_eq(_what)'");
+      });
+      it('public', async () => {
+        const t = toString(await asset.methods.un_get_symbol().view());
+        expect(t).toBe(TOKEN_SYMBOL);
 
-      await expect(reader.methods.check_symbol(asset.address, 'WRONG_SYMBOL').simulate()).rejects.toThrowError(
-        "Failed to solve brillig function, reason: explicit trap hit in brillig 'symbol.is_eq(_what)'",
-      );
+        const tx = reader.methods.check_symbol_public(asset.address, TOKEN_SYMBOL).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
+
+        await expect(reader.methods.check_symbol_public(asset.address, 'WRONG_SYMBOL').simulate()).rejects.toThrowError(
+          "Failed to solve brillig function, reason: explicit trap hit in brillig 'symbol.is_eq(_what)'",
+        );
+      });
     });
 
-    it('decimals', async () => {
-      const t = await asset.methods.un_get_decimals().view();
-      expect(t).toBe(TOKEN_DECIMALS);
+    describe('decimals', () => {
+      it('private', async () => {
+        const t = await asset.methods.un_get_decimals().view();
+        expect(t).toBe(TOKEN_DECIMALS);
 
-      const tx = reader.methods.check_decimals(asset.address, TOKEN_DECIMALS).send();
-      const receipt = await tx.wait();
-      expect(receipt.status).toBe(TxStatus.MINED);
+        const tx = reader.methods.check_decimals_private(asset.address, TOKEN_DECIMALS).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
 
-      await expect(reader.methods.check_decimals(asset.address, 99).simulate()).rejects.toThrowError(
-        "Failed to solve brillig function, reason: explicit trap hit in brillig 'ret[0] as u8 == what'",
-      );
+        await expect(reader.methods.check_decimals_private(asset.address, 99).simulate()).rejects.toThrowError(
+          "Cannot satisfy constraint 'ret[0] as u8 == what'",
+        );
+      });
+
+      it('public', async () => {
+        const t = await asset.methods.un_get_decimals().view();
+        expect(t).toBe(TOKEN_DECIMALS);
+
+        const tx = reader.methods.check_decimals_public(asset.address, TOKEN_DECIMALS).send();
+        const receipt = await tx.wait();
+        expect(receipt.status).toBe(TxStatus.MINED);
+
+        await expect(reader.methods.check_decimals_public(asset.address, 99).simulate()).rejects.toThrowError(
+          "Failed to solve brillig function, reason: explicit trap hit in brillig 'ret[0] as u8 == what'",
+        );
+      });
     });
   });
 

yarn-project/noir-contracts/contracts/docs_example_contract/src/main.nr

@@ -46,7 +46,9 @@ contract DocsExample {
         // docs:end:storage-map-singleton-declaration
         test: Set<CardNote>,
         imm_singleton: ImmutableSingleton<CardNote>,
+        // docs:start:start_vars_stable
         stable_value: StablePublicState<Leader>,
+        // docs:end:start_vars_stable
     }
 
     impl Storage {

yarn-project/noir-contracts/contracts/reader_contract/src/main.nr

@@ -11,27 +11,52 @@ contract Reader {
     fn constructor() {}
 
     #[aztec(public)]
-    fn check_name(who: AztecAddress, what: str<31>) {
+    fn check_name_public(who: AztecAddress, what: str<31>) {
         let selector = FunctionSelector::from_signature("public_get_name()");
         let ret = context.call_public_function_no_args(who, selector);
         let name = FieldCompressedString::from_field(ret[0]);
         let _what = FieldCompressedString::from_string(what);
         assert(name.is_eq(_what));
     }
 
+    #[aztec(private)]
+        fn check_name_private(who: AztecAddress, what: str<31>) {
+        let selector = FunctionSelector::from_signature("private_get_name()");
+        let ret = context.call_private_function_no_args(who, selector);
+        let name = FieldCompressedString::from_field(ret[0]);
+        let _what = FieldCompressedString::from_string(what);
+        assert(name.is_eq(_what));
+    }
+
     #[aztec(public)]
-    fn check_symbol(who: AztecAddress, what: str<31>) {
+    fn check_symbol_public(who: AztecAddress, what: str<31>) {
         let selector = FunctionSelector::from_signature("public_get_symbol()");
         let ret = context.call_public_function_no_args(who, selector);
         let symbol = FieldCompressedString::from_field(ret[0]);
         let _what = FieldCompressedString::from_string(what);
         assert(symbol.is_eq(_what));
     }
 
+    #[aztec(private)]
+    fn check_symbol_private(who: AztecAddress, what: str<31>) {
+        let selector = FunctionSelector::from_signature("private_get_symbol()");
+        let ret = context.call_private_function_no_args(who, selector);
+        let symbol = FieldCompressedString::from_field(ret[0]);
+        let _what = FieldCompressedString::from_string(what);
+        assert(symbol.is_eq(_what));
+    }
+
     #[aztec(public)]
-    fn check_decimals(who: AztecAddress, what: u8) {
+    fn check_decimals_public(who: AztecAddress, what: u8) {
         let selector = FunctionSelector::from_signature("public_get_decimals()");
         let ret = context.call_public_function_no_args(who, selector);
         assert(ret[0] as u8 == what);
     }
+
+    #[aztec(private)]
+    fn check_decimals_private(who: AztecAddress, what: u8) {
+        let selector = FunctionSelector::from_signature("private_get_decimals()");
+        let ret = context.call_private_function_no_args(who, selector);
+        assert(ret[0] as u8 == what);
+    }
 }

yarn-project/noir-contracts/contracts/token_contract/src/main.nr

@@ -24,7 +24,7 @@ contract Token {
         },
         context::{PrivateContext, PublicContext, Context},
         hash::{compute_secret_hash},
-        state_vars::{map::Map, public_state::PublicState, set::Set},
+        state_vars::{map::Map, public_state::PublicState, stable_public_state::StablePublicState,  set::Set},
         protocol_types::{
             type_serialization::{
                 FIELD_SERIALIZED_LEN, 
@@ -69,9 +69,11 @@ contract Token {
         pending_shields: Set<TransparentNote>,
         // docs:end:storage_pending_shields
         public_balances: Map<AztecAddress, PublicState<SafeU120>>,
-        symbol: PublicState<FieldCompressedString>,
-        name: PublicState<FieldCompressedString>,
-        decimals: PublicState<u8>,
+        symbol: StablePublicState<FieldCompressedString>,
+        name: StablePublicState<FieldCompressedString>,
+        // docs:start:storage_decimals
+        decimals: StablePublicState<u8>,
+        // docs:end:storage_decimals
     }
     // docs:end:storage_struct
 
@@ -117,18 +119,20 @@ contract Token {
                         )
                     },
                 ),
-                symbol: PublicState::new(
+                symbol: StablePublicState::new(
                     context,
                     7,
                 ),
-                name: PublicState::new(
+                name: StablePublicState::new(
                     context,
                     8,
                 ),
-                decimals: PublicState::new(
+                // docs:start:storage_decimals_init
+                decimals: StablePublicState::new(
                     context,
                     9,
                 ),
+                // docs:end:storage_decimals_init
             }
         }
     }
@@ -160,29 +164,48 @@ contract Token {
 
     #[aztec(public)]
     fn public_get_name() -> pub FieldCompressedString {
-        storage.name.read()
+        storage.name.read_public()
+    }
+
+    #[aztec(private)]
+    fn private_get_name() -> pub FieldCompressedString {
+        storage.name.read_private()
     }
 
     unconstrained fn un_get_name() -> pub [u8; 31] {
-        storage.name.read().to_bytes()
+        storage.name.read_public().to_bytes()
     }
 
     #[aztec(public)]
     fn public_get_symbol() -> pub FieldCompressedString {
-        storage.symbol.read()
+        storage.symbol.read_public()
+    }
+
+    #[aztec(private)]
+    fn private_get_symbol() -> pub FieldCompressedString {
+        storage.symbol.read_private()
     }
 
     unconstrained fn un_get_symbol() -> pub [u8; 31] {
-        storage.symbol.read().to_bytes()
+        storage.symbol.read_public().to_bytes()
     }
 
     #[aztec(public)]
     fn public_get_decimals() -> pub u8 {
-        storage.decimals.read()
+        // docs:start:read_decimals_public
+        storage.decimals.read_public()
+        // docs:end:read_decimals_public
+    }
+
+    #[aztec(private)]
+    fn private_get_decimals() -> pub u8 {
+        // docs:start:read_decimals_private
+        storage.decimals.read_private()
+        // docs:end:read_decimals_private
     }
 
     unconstrained fn un_get_decimals() -> pub u8 {
-        storage.decimals.read()
+        storage.decimals.read_public()
     }
 
     // docs:start:set_minter
@@ -366,9 +389,11 @@ contract Token {
         assert(!new_admin.is_zero(), "invalid admin");
         storage.admin.write(new_admin);
         storage.minters.at(new_admin).write(true);
-        storage.name.write(name);
-        storage.symbol.write(symbol);
-        storage.decimals.write(decimals);
+        storage.name.initialize(name);
+        storage.symbol.initialize(symbol);
+        // docs:start:initialize_decimals
+        storage.decimals.initialize(decimals);
+        // docs:end:initialize_decimals
     }
     // docs:end:initialize