perf: Introduce RcStr (vercel/turborepo#8221)

### Description

If we accept `: String` from a function, invoking the function needs one
owned `String` and it means allocation even if the value isn't changed.
But with this PR, functions now accept `RcStr`, which is shared, so
invoking the same function with the same value does not involve
allocation for `String` .

---

I tried using `Arc<String>` in
vercel/turborepo#7772, but a team member suggested
creating a new type so we can replace underlying implementation easily
in the future.

I used `ast-grep` with

```yml
id: convert-expr-into
language: rust
rule:
  kind: function_item
  all:
    - has:
        kind: parameters
        pattern: $PARAMS
    - any:
      - has:
          kind: visibility_modifier
          pattern: $VIS
      - not:
          has:
            kind: visibility_modifier

    - any:
      - has:
          kind: function_modifiers
          pattern: $MOD
      - not:
          has:
            kind: function_modifiers
    - has:
        field: return_type
        pattern: $RET
    - has:
        field: body
        pattern: $BODY
    - has:
        kind: identifier
        pattern: $NAME
    - follows:
        kind: attribute_item
        pattern: '#[turbo_tasks::function]'



transform:
  NEW_PARAMS:
    replace:
      replace: 'String'
      by: 'RcStr'
      source: $PARAMS

fix:
  $VIS $MOD fn $NAME $NEW_PARAMS -> $RET $BODY




```


### Performance difference:

#### `main`:

```
Benchmarking bench_startup/Next.js canary Turbo SSR/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 65.6s.
bench_startup/Next.js canary Turbo SSR/1000 modules
                        time:   [4.1476 s 4.1625 s 4.1752 s]
Benchmarking bench_startup/Next.js canary Turbo RSC/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 63.5s.
bench_startup/Next.js canary Turbo RSC/1000 modules
                        time:   [4.0396 s 4.0673 s 4.0956 s]
Benchmarking bench_startup/Next.js canary Turbo RCC/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 69.7s.
bench_startup/Next.js canary Turbo RCC/1000 modules
                        time:   [4.7222 s 4.7508 s 4.7790 s]
```

#### `pr`:

```
Benchmarking bench_startup/Next.js canary Turbo SSR/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 66.2s.
bench_startup/Next.js canary Turbo SSR/1000 modules
                        time:   [4.1175 s 4.1310 s 4.1496 s]
Found 1 outliers among 10 measurements (10.00%)
  1 (10.00%) high severe
Benchmarking bench_startup/Next.js canary Turbo RSC/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 63.7s.
bench_startup/Next.js canary Turbo RSC/1000 modules
                        time:   [4.0401 s 4.0714 s 4.1105 s]
Found 1 outliers among 10 measurements (10.00%)
  1 (10.00%) high mild
Benchmarking bench_startup/Next.js canary Turbo RCC/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 70.2s.
bench_startup/Next.js canary Turbo RCC/1000 modules
                        time:   [4.6696 s 4.6900 s 4.7107 s]
Benchmarking bench_startup/Next.js 14 Turbo SSR/1000 modules: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 60.0s. You may wish to increase target time to 63.9s.
```

---------

Co-authored-by: Benjamin Woodruff <benjamin.woodruff@vercel.com>

crates/node-file-trace/src/lib.rs

@@ -22,8 +22,8 @@ use serde::Deserialize;
 use serde::Serialize;
 use tokio::sync::mpsc::channel;
 use turbo_tasks::{
-    backend::Backend, util::FormatDuration, TaskId, TransientInstance, TransientValue, TurboTasks,
-    UpdateInfo, Value, Vc,
+    backend::Backend, util::FormatDuration, RcStr, TaskId, TransientInstance, TransientValue,
+    TurboTasks, UpdateInfo, Value, Vc,
 };
 use turbo_tasks_fs::{
     glob::Glob, DirectoryEntry, DiskFileSystem, FileSystem, FileSystemPath, ReadGlobResult,
@@ -188,7 +188,7 @@ impl Args {
 }
 
 async fn create_fs(name: &str, root: &str, watch: bool) -> Result<Vc<Box<dyn FileSystem>>> {
-    let fs = DiskFileSystem::new(name.to_string(), root.to_string(), vec![]);
+    let fs = DiskFileSystem::new(name.into(), root.into(), vec![]);
     if watch {
         fs.await?.start_watching()?;
     } else {
@@ -232,17 +232,17 @@ async fn add_glob_results(
 #[turbo_tasks::function]
 async fn input_to_modules(
     fs: Vc<Box<dyn FileSystem>>,
-    input: Vec<String>,
+    input: Vec<RcStr>,
     exact: bool,
-    process_cwd: Option<String>,
-    context_directory: String,
+    process_cwd: Option<RcStr>,
+    context_directory: RcStr,
     module_options: TransientInstance<ModuleOptionsContext>,
     resolve_options: TransientInstance<ResolveOptionsContext>,
 ) -> Result<Vc<Modules>> {
     let root = fs.root();
     let process_cwd = process_cwd
         .clone()
-        .map(|p| format!("/ROOT{}", p.trim_start_matches(&context_directory)));
+        .map(|p| format!("/ROOT{}", p.trim_start_matches(&*context_directory)).into());
 
     let asset_context: Vc<Box<dyn AssetContext>> = Vc::upcast(create_module_asset(
         root,
@@ -283,7 +283,7 @@ fn process_context(dir: &Path, context_directory: Option<&String>) -> Result<Str
         .to_string())
 }
 
-fn make_relative_path(dir: &Path, context_directory: &str, input: &str) -> Result<String> {
+fn make_relative_path(dir: &Path, context_directory: &str, input: &str) -> Result<RcStr> {
     let mut input = PathBuf::from(input);
     if !input.is_absolute() {
         input = dir.join(input);
@@ -299,10 +299,11 @@ fn make_relative_path(dir: &Path, context_directory: &str, input: &str) -> Resul
     Ok(input
         .to_str()
         .ok_or_else(|| anyhow!("input contains invalid characters"))?
-        .replace('\\', "/"))
+        .replace('\\', "/")
+        .into())
 }
 
-fn process_input(dir: &Path, context_directory: &str, input: &[String]) -> Result<Vec<String>> {
+fn process_input(dir: &Path, context_directory: &str, input: &[String]) -> Result<Vec<RcStr>> {
     input
         .iter()
         .map(|input| make_relative_path(dir, context_directory, input))
@@ -314,7 +315,7 @@ pub async fn start(
     turbo_tasks: Option<&Arc<TurboTasks<MemoryBackend>>>,
     module_options: Option<ModuleOptionsContext>,
     resolve_options: Option<ResolveOptionsContext>,
-) -> Result<Vec<String>> {
+) -> Result<Vec<RcStr>> {
     register();
     let &CommonArgs {
         memory_limit,
@@ -394,7 +395,7 @@ async fn run<B: Backend + 'static, F: Future<Output = ()>>(
     final_finish: impl FnOnce(Arc<TurboTasks<B>>, TaskId, Duration) -> F,
     module_options: Option<ModuleOptionsContext>,
     resolve_options: Option<ResolveOptionsContext>,
-) -> Result<Vec<String>> {
+) -> Result<Vec<RcStr>> {
     let &CommonArgs {
         watch,
         show_all,
@@ -494,7 +495,7 @@ async fn run<B: Backend + 'static, F: Future<Output = ()>>(
             if has_return_value {
                 let output_read_ref = output.await?;
                 let output_iter = output_read_ref.iter().cloned();
-                sender.send(output_iter.collect::<Vec<String>>()).await?;
+                sender.send(output_iter.collect::<Vec<RcStr>>()).await?;
                 drop(sender);
             }
             Ok::<Vc<()>, _>(Default::default())
@@ -515,7 +516,7 @@ async fn main_operation(
     args: TransientInstance<Args>,
     module_options: TransientInstance<ModuleOptionsContext>,
     resolve_options: TransientInstance<ResolveOptionsContext>,
-) -> Result<Vc<Vec<String>>> {
+) -> Result<Vc<Vec<RcStr>>> {
     let dir = current_dir.into_value();
     let args = &*args;
     let &CommonArgs {
@@ -526,8 +527,11 @@ async fn main_operation(
         ref process_cwd,
         ..
     } = args.common();
-    let context_directory = process_context(&dir, context_directory.as_ref()).unwrap();
+    let context_directory: RcStr = process_context(&dir, context_directory.as_ref())
+        .unwrap()
+        .into();
     let fs = create_fs("context directory", &context_directory, watch).await?;
+    let process_cwd = process_cwd.clone().map(RcStr::from);
 
     match *args {
         Args::Print { common: _ } => {
@@ -549,7 +553,7 @@ async fn main_operation(
                     .await?;
                 for asset in set.await?.iter() {
                     let path = asset.ident().path().await?;
-                    result.insert(path.path.to_string());
+                    result.insert(RcStr::from(&*path.path));
                 }
             }
 
@@ -620,7 +624,7 @@ async fn main_operation(
 #[turbo_tasks::function]
 async fn create_module_asset(
     root: Vc<FileSystemPath>,
-    process_cwd: Option<String>,
+    process_cwd: Option<RcStr>,
     module_options: TransientInstance<ModuleOptionsContext>,
     resolve_options: TransientInstance<ResolveOptionsContext>,
 ) -> Result<Vc<ModuleAssetContext>> {
@@ -635,12 +639,12 @@ async fn create_module_asset(
     let glob_mappings = vec![
         (
             root,
-            Glob::new("**/*/next/dist/server/next.js".to_string()),
+            Glob::new("**/*/next/dist/server/next.js".into()),
             ImportMapping::Ignore.into(),
         ),
         (
             root,
-            Glob::new("**/*/next/dist/bin/next".to_string()),
+            Glob::new("**/*/next/dist/bin/next".into()),
             ImportMapping::Ignore.into(),
         ),
     ];
@@ -662,7 +666,7 @@ async fn create_module_asset(
         compile_time_info,
         ModuleOptionsContext::clone(&*module_options).cell(),
         resolve_options.cell(),
-        Vc::cell("node_file_trace".to_string()),
+        Vc::cell("node_file_trace".into()),
     ))
 }
 

crates/node-file-trace/src/nft_json.rs

@@ -29,7 +29,9 @@ impl OutputAsset for NftJsonAsset {
     async fn ident(&self) -> Result<Vc<AssetIdent>> {
         let path = self.entry.ident().path().await?;
         Ok(AssetIdent::from_path(
-            path.fs.root().join(format!("{}.nft.json", path.path)),
+            path.fs
+                .root()
+                .join(format!("{}.nft.json", path.path).into()),
         ))
     }
 }

crates/turbo-tasks-env/src/command_line.rs

@@ -1,5 +1,5 @@
 use indexmap::IndexMap;
-use turbo_tasks::Vc;
+use turbo_tasks::{RcStr, Vc};
 
 use crate::{sorted_env_vars, EnvMap, ProcessEnv, GLOBAL_ENV_LOCK};
 
@@ -16,7 +16,7 @@ impl CommandLineProcessEnv {
 }
 
 /// Clones the current env vars into a IndexMap.
-fn env_snapshot() -> IndexMap<String, String> {
+fn env_snapshot() -> IndexMap<RcStr, RcStr> {
     let _lock = GLOBAL_ENV_LOCK.lock().unwrap();
     sorted_env_vars()
 }

crates/turbo-tasks-env/src/custom.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use turbo_tasks::Vc;
+use turbo_tasks::{RcStr, Vc};
 
 use crate::{case_insensitive_read, EnvMap, ProcessEnv};
 
@@ -32,7 +32,7 @@ impl ProcessEnv for CustomProcessEnv {
     }
 
     #[turbo_tasks::function]
-    async fn read(&self, name: String) -> Result<Vc<Option<String>>> {
+    async fn read(&self, name: RcStr) -> Result<Vc<Option<RcStr>>> {
         let custom = case_insensitive_read(self.custom, name.clone());
         match &*custom.await? {
             Some(_) => Ok(custom),

crates/turbo-tasks-env/src/dotenv.rs

@@ -2,7 +2,7 @@ use std::{env, sync::MutexGuard};
 
 use anyhow::{anyhow, Context, Result};
 use indexmap::IndexMap;
-use turbo_tasks::{ValueToString, Vc};
+use turbo_tasks::{RcStr, ValueToString, Vc};
 use turbo_tasks_fs::{FileContent, FileSystemPath};
 
 use crate::{sorted_env_vars, EnvMap, ProcessEnv, GLOBAL_ENV_LOCK};
@@ -84,11 +84,7 @@ impl ProcessEnv for DotenvProcessEnv {
 }
 
 /// Restores the global env variables to mirror `to`.
-fn restore_env(
-    from: &IndexMap<String, String>,
-    to: &IndexMap<String, String>,
-    _lock: &MutexGuard<()>,
-) {
+fn restore_env(from: &IndexMap<RcStr, RcStr>, to: &IndexMap<RcStr, RcStr>, _lock: &MutexGuard<()>) {
     for key in from.keys() {
         if !to.contains_key(key) {
             env::remove_var(key);

crates/turbo-tasks-env/src/filter.rs

@@ -1,6 +1,6 @@
 use anyhow::Result;
 use indexmap::IndexMap;
-use turbo_tasks::Vc;
+use turbo_tasks::{RcStr, Vc};
 
 use crate::{EnvMap, ProcessEnv};
 
@@ -9,16 +9,19 @@ use crate::{EnvMap, ProcessEnv};
 #[turbo_tasks::value]
 pub struct FilterProcessEnv {
     prior: Vc<Box<dyn ProcessEnv>>,
-    filters: Vec<String>,
+    filters: Vec<RcStr>,
 }
 
 #[turbo_tasks::value_impl]
 impl FilterProcessEnv {
     #[turbo_tasks::function]
-    pub fn new(prior: Vc<Box<dyn ProcessEnv>>, filters: Vec<String>) -> Vc<Self> {
+    pub fn new(prior: Vc<Box<dyn ProcessEnv>>, filters: Vec<RcStr>) -> Vc<Self> {
         FilterProcessEnv {
             prior,
-            filters: filters.into_iter().map(|f| f.to_uppercase()).collect(),
+            filters: filters
+                .into_iter()
+                .map(|f| f.to_uppercase().into())
+                .collect(),
         }
         .cell()
     }
@@ -33,7 +36,7 @@ impl ProcessEnv for FilterProcessEnv {
         for (key, value) in &*prior {
             let uppercase = key.to_uppercase();
             for filter in &self.filters {
-                if uppercase.starts_with(filter) {
+                if uppercase.starts_with(&**filter) {
                     filtered.insert(key.clone(), value.clone());
                     break;
                 }
@@ -43,9 +46,9 @@ impl ProcessEnv for FilterProcessEnv {
     }
 
     #[turbo_tasks::function]
-    fn read(&self, name: String) -> Vc<Option<String>> {
+    fn read(&self, name: RcStr) -> Vc<Option<RcStr>> {
         for filter in &self.filters {
-            if name.to_uppercase().starts_with(filter) {
+            if name.to_uppercase().starts_with(&**filter) {
                 return self.prior.read(name);
             }
         }

crates/turbo-tasks-env/src/lib.rs

@@ -9,15 +9,15 @@ use std::{env, sync::Mutex};
 
 use anyhow::Result;
 use indexmap::IndexMap;
-use turbo_tasks::Vc;
+use turbo_tasks::{RcStr, Vc};
 
 pub use self::{
     command_line::CommandLineProcessEnv, custom::CustomProcessEnv, dotenv::DotenvProcessEnv,
     filter::FilterProcessEnv,
 };
 
 #[turbo_tasks::value(transparent)]
-pub struct EnvMap(#[turbo_tasks(trace_ignore)] IndexMap<String, String>);
+pub struct EnvMap(#[turbo_tasks(trace_ignore)] IndexMap<RcStr, RcStr>);
 
 #[turbo_tasks::value_impl]
 impl EnvMap {
@@ -35,7 +35,7 @@ impl ProcessEnv for EnvMap {
     }
 
     #[turbo_tasks::function]
-    async fn read(self: Vc<Self>, name: String) -> Vc<Option<String>> {
+    async fn read(self: Vc<Self>, name: RcStr) -> Vc<Option<RcStr>> {
         case_insensitive_read(self, name)
     }
 }
@@ -51,23 +51,25 @@ pub trait ProcessEnv {
     fn read_all(self: Vc<Self>) -> Vc<EnvMap>;
 
     /// Reads a single env variable. Ignores casing.
-    fn read(self: Vc<Self>, name: String) -> Vc<Option<String>> {
+    fn read(self: Vc<Self>, name: RcStr) -> Vc<Option<RcStr>> {
         case_insensitive_read(self.read_all(), name)
     }
 }
 
-pub fn sorted_env_vars() -> IndexMap<String, String> {
-    let mut vars = env::vars().collect::<IndexMap<_, _>>();
+pub fn sorted_env_vars() -> IndexMap<RcStr, RcStr> {
+    let mut vars = env::vars()
+        .map(|(k, v)| (k.into(), v.into()))
+        .collect::<IndexMap<_, _>>();
     vars.sort_keys();
     vars
 }
 
 #[turbo_tasks::function]
-pub async fn case_insensitive_read(map: Vc<EnvMap>, name: String) -> Result<Vc<Option<String>>> {
+pub async fn case_insensitive_read(map: Vc<EnvMap>, name: RcStr) -> Result<Vc<Option<RcStr>>> {
     Ok(Vc::cell(
         to_uppercase_map(map)
             .await?
-            .get(&name.to_uppercase())
+            .get(&RcStr::from(name.to_uppercase()))
             .cloned(),
     ))
 }
@@ -77,7 +79,7 @@ async fn to_uppercase_map(map: Vc<EnvMap>) -> Result<Vc<EnvMap>> {
     let map = &*map.await?;
     let mut new = IndexMap::with_capacity(map.len());
     for (k, v) in map {
-        new.insert(k.to_uppercase(), v.clone());
+        new.insert(k.to_uppercase().into(), v.clone());
     }
     Ok(Vc::cell(new))
 }