Implement StorageString to std-lib (FuelLabs#4725)

## Description

The `String` type has recently been move/introduced to the std-lib. This
is a heap type and does not allow for any storage. The `StorageString`
type allows for storage.

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: bitzoic <[email protected]>

sway-lib-std/src/storage.sw

@@ -7,3 +7,4 @@ pub mod storable_slice;
 pub mod storage_map;
 pub mod storage_vec;
 pub mod storage_bytes;
+pub mod storage_string;

sway-lib-std/src/storage/storage_string.sw

@@ -0,0 +1,144 @@
+library;
+
+use ::bytes::Bytes;
+use ::option::Option;
+use ::storage::storable_slice::*;
+use ::storage::storage_api::read;
+use ::string::String;
+
+pub struct StorageString {}
+
+impl StorableSlice<String> for StorageKey<StorageString> {
+    /// Takes a `String` type and saves the underlying data in storage.
+    ///
+    /// ### Arguments
+    ///
+    /// * `string` - The string which will be stored.
+    ///
+    /// ### Number of Storage Accesses
+    ///
+    /// * Writes: `2`
+    ///
+    /// ### Examples
+    ///
+    /// ```sway
+    /// storage {
+    ///     stored_string: StorageString = StorageString {}
+    /// }
+    ///
+    /// fn foo() {
+    ///     let mut bytes = Bytes::new();
+    ///     bytes.push(5_u8);
+    ///     bytes.push(7_u8);
+    ///     bytes.push(9_u8);
+    ///     let string = String::from(bytes);
+    /// 
+    ///     storage.stored_string.write_slice(string);
+    /// }
+    /// ```
+    #[storage(read, write)]
+    fn write_slice(self, string: String) {
+        write_slice(self.slot, string.as_raw_slice());
+    }
+
+    /// Constructs a `String` type from storage.
+    ///
+    /// ### Number of Storage Accesses
+    ///
+    /// * Reads: `2`
+    ///
+    /// ### Examples
+    ///
+    /// ```sway
+    /// storage {
+    ///     stored_string: StorageString = StorageString {}
+    /// }
+    ///
+    /// fn foo() {
+    ///     let mut bytes = Bytes::new();
+    ///     bytes.push(5_u8);
+    ///     bytes.push(7_u8);
+    ///     bytes.push(9_u8);
+    ///     let string = String::from(bytes);
+    ///
+    ///     assert(storage.stored_string.read_slice(key).is_none());
+    ///     storage.stored_string.write_slice(string);
+    ///     let retrieved_string = storage.stored_string.read_slice(key).unwrap();
+    ///     assert(string == retrieved_string);
+    /// }
+    /// ```
+    #[storage(read)]
+    fn read_slice(self) -> Option<String> {
+        match read_slice(self.slot) {
+            Option::Some(slice) => {
+                Option::Some(String::from(slice))
+            },
+            Option::None => Option::None,
+        }
+    }
+
+    /// Clears a stored `String` in storage.
+    ///
+    /// ### Number of Storage Accesses
+    ///
+    /// * Reads: `1`
+    /// * Clears: `2`
+    ///
+    /// ### Examples
+    ///
+    /// ```sway
+    /// storage {
+    ///     stored_string: StorageString = StorageString {}
+    /// }
+    ///
+    /// fn foo() {
+    ///     let mut bytes = Bytes::new();
+    ///     bytes.push(5_u8);
+    ///     bytes.push(7_u8);
+    ///     bytes.push(9_u8);
+    ///     let string = String::from(bytes);
+    /// 
+    ///     storage.stored_string.write_slice(string);
+    ///
+    ///     assert(storage.stored_string.read_slice(key).is_some());
+    ///     let cleared = storage.stored_string.clear();
+    ///     assert(cleared);
+    ///     let retrieved_string = storage.stored_string.read_slice(key);
+    ///     assert(retrieved_string.is_none());
+    /// }
+    /// ```
+    #[storage(read, write)]
+    fn clear(self) -> bool {
+        clear_slice(self.slot)
+    }
+
+    /// Returns the length of `String` in storage.
+    ///
+    /// ### Number of Storage Accesses
+    ///
+    /// * Reads: `1`
+    ///
+    /// ### Examples
+    ///
+    /// ```sway
+    /// storage {
+    ///     stored_string: StorageString = StorageString {}
+    /// }
+    ///
+    /// fn foo() {
+    ///     let mut bytes = Bytes::new();
+    ///     bytes.push(5_u8);
+    ///     bytes.push(7_u8);
+    ///     bytes.push(9_u8);
+    ///     let string = String::from(bytes);
+    /// 
+    ///     assert(storage.stored_string.len() == 0)
+    ///     storage.stored_string.write_slice(string);
+    ///     assert(storage.stored_string.len() == 3);
+    /// }
+    /// ```
+    #[storage(read)]
+    fn len(self) -> u64 {
+        read::<u64>(self.slot, 0).unwrap_or(0)
+    }
+}

test/src/sdk-harness/Forc.lock

@@ -251,6 +251,11 @@ name = 'storage_map_nested'
 source = 'member'
 dependencies = ['std']
 
+[[package]]
+name = 'storage_string'
+source = 'member'
+dependencies = ['std']
+
 [[package]]
 name = 'storage_vec_nested'
 source = 'member'

test/src/sdk-harness/Forc.toml

@@ -30,6 +30,7 @@ members = [
   "test_projects/storage_init",
   "test_projects/storage_map",
   "test_projects/storage_map_nested",
+  "test_projects/storage_string",
   "test_projects/storage_vec_nested",
   "test_projects/token_ops",
   "test_projects/tx_fields",

test/src/sdk-harness/test_projects/harness.rs

@@ -32,6 +32,7 @@ mod storage_bytes;
 mod storage_init;
 mod storage_map;
 mod storage_map_nested;
+mod storage_string;
 mod storage_vec;
 mod storage_vec_nested;
 mod token_ops;

test/src/sdk-harness/test_projects/storage_string/.gitignore

@@ -0,0 +1,2 @@
+out
+target

test/src/sdk-harness/test_projects/storage_string/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = 'core'
+source = 'path+from-root-26685F36F0140A56'
+
+[[package]]
+name = 'std'
+source = 'path+from-root-26685F36F0140A56'
+dependencies = ['core']
+
+[[package]]
+name = 'storage_string'
+source = 'member'
+dependencies = ['std']

test/src/sdk-harness/test_projects/storage_string/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "storage_string"
+
+[dependencies]
+std = { path = "../../../../../sway-lib-std" }