refactor(language_server): introduce LSPFileSystem (#13731)

Formatting requests has no source text included:
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#documentFormattingParams

Because users can format in memory files, the server needs to keep track of the changes.
Created in `Backend` struct, so when we later support `textDocument/diagnostic` (we support currently only `textDocument/publishDiagnostic)`, we can use the same File System for it too :)

Putting the struct into a Workspace Worker is an option too, but there can be multiple of it.
With this solution, there is only one instance of it :)

Author: Sysix

crates/oxc_language_server/src/capabilities.rs

@@ -14,6 +14,7 @@ pub struct Capabilities {
     pub workspace_execute_command: bool,
     pub workspace_configuration: bool,
     pub dynamic_watchers: bool,
+    pub dynamic_formatting: bool,
 }
 
 impl From<ClientCapabilities> for Capabilities {
@@ -39,13 +40,20 @@ impl From<ClientCapabilities> for Capabilities {
                 watched_files.dynamic_registration.is_some_and(|dynamic| dynamic)
             })
         });
+        // TODO: enable it when we support formatting
+        // let formatting = value.text_document.as_ref().is_some_and(|text_document| {
+        //     text_document.formatting.is_some_and(|formatting| {
+        //         formatting.dynamic_registration.is_some_and(|dynamic| dynamic)
+        //     })
+        // });
 
         Self {
             code_action_provider,
             workspace_apply_edit,
             workspace_execute_command,
             workspace_configuration,
             dynamic_watchers,
+            dynamic_formatting: false,
         }
     }
 }

crates/oxc_language_server/src/file_system.rs

@@ -0,0 +1,27 @@
+use tower_lsp_server::lsp_types::Uri;
+
+use crate::ConcurrentHashMap;
+
+#[derive(Debug, Default)]
+pub struct LSPFileSystem {
+    files: ConcurrentHashMap<Uri, String>,
+}
+
+impl LSPFileSystem {
+    pub fn clear(&self) {
+        self.files.pin().clear();
+    }
+
+    pub fn set(&self, uri: &Uri, content: String) {
+        self.files.pin().insert(uri.clone(), content);
+    }
+
+    #[expect(dead_code)] // used for the oxc_formatter in the future
+    pub fn get(&self, uri: &Uri) -> Option<String> {
+        self.files.pin().get(uri).cloned()
+    }
+
+    pub fn remove(&self, uri: &Uri) {
+        self.files.pin().remove(uri);
+    }
+}

crates/oxc_language_server/src/main.rs

@@ -22,6 +22,7 @@ use tower_lsp_server::{
 mod capabilities;
 mod code_actions;
 mod commands;
+mod file_system;
 mod formatter;
 mod linter;
 mod options;
@@ -36,6 +37,8 @@ use linter::server_linter::ServerLinterRun;
 use options::{Options, WorkspaceOption};
 use worker::WorkspaceWorker;
 
+use crate::file_system::LSPFileSystem;
+
 type ConcurrentHashMap<K, V> = papaya::HashMap<K, V, FxBuildHasher>;
 
 const OXC_CONFIG_FILE: &str = ".oxlintrc.json";
@@ -51,6 +54,7 @@ struct Backend {
     // 2. `workspace/didChangeWorkspaceFolders` request
     workspace_workers: Arc<RwLock<Vec<WorkspaceWorker>>>,
     capabilities: OnceCell<Capabilities>,
+    file_system: Arc<RwLock<LSPFileSystem>>,
 }
 
 impl LanguageServer for Backend {
@@ -203,6 +207,9 @@ impl LanguageServer for Backend {
 
     async fn shutdown(&self) -> Result<()> {
         self.clear_all_diagnostics().await;
+        if self.capabilities.get().is_some_and(|option| option.dynamic_formatting) {
+            self.file_system.write().await.clear();
+        }
         Ok(())
     }
 
@@ -444,6 +451,12 @@ impl LanguageServer for Backend {
         let Some(worker) = workers.iter().find(|worker| worker.is_responsible_for_uri(uri)) else {
             return;
         };
+
+        if self.capabilities.get().is_some_and(|option| option.dynamic_formatting) {
+            // saving the file means we can read again from the file system
+            self.file_system.write().await.remove(uri);
+        }
+
         if let Some(diagnostics) = worker.lint_file(uri, None, ServerLinterRun::OnSave).await {
             self.client
                 .publish_diagnostics(
@@ -464,6 +477,13 @@ impl LanguageServer for Backend {
             return;
         };
         let content = params.content_changes.first().map(|c| c.text.clone());
+
+        if self.capabilities.get().is_some_and(|option| option.dynamic_formatting)
+            && let Some(content) = &content
+        {
+            self.file_system.write().await.set(uri, content.to_string());
+        }
+
         if let Some(diagnostics) = worker.lint_file(uri, content, ServerLinterRun::OnType).await {
             self.client
                 .publish_diagnostics(
@@ -483,6 +503,11 @@ impl LanguageServer for Backend {
         };
 
         let content = params.text_document.text;
+
+        if self.capabilities.get().is_some_and(|option| option.dynamic_formatting) {
+            self.file_system.write().await.set(uri, content.to_string());
+        }
+
         if let Some(diagnostics) =
             worker.lint_file(uri, Some(content), ServerLinterRun::Always).await
         {
@@ -502,6 +527,9 @@ impl LanguageServer for Backend {
         let Some(worker) = workers.iter().find(|worker| worker.is_responsible_for_uri(uri)) else {
             return;
         };
+        if self.capabilities.get().is_some_and(|option| option.dynamic_formatting) {
+            self.file_system.write().await.remove(uri);
+        }
         worker.remove_diagnostics(&params.text_document.uri).await;
     }
 
@@ -626,6 +654,7 @@ async fn main() {
         client,
         workspace_workers: Arc::new(RwLock::new(vec![])),
         capabilities: OnceCell::new(),
+        file_system: Arc::new(RwLock::new(LSPFileSystem::default())),
     })
     .finish();