ruff server: Introduce the ruff.printDebugInformation command (#11831)

## Summary

Closes #11715.

Introduces a new command, `ruff.printDebugInformation`. This will print
useful information about the status of the server to `stderr`.

Right now, the information shown by this command includes:
* The path to the server executable
* The version of the executable
* The text encoding being used
* The number of open documents and workspaces
* A list of registered configuration files
* The capabilities of the client

## Test Plan

First, checkout and use [the corresponding `ruff-vscode`
PR](https://github.com/astral-sh/ruff-vscode/pull/495).

Running the `Print debug information` command in VS Code should show
something like the following in the Output channel:

<img width="991" alt="Screenshot 2024-06-11 at 11 41 46 AM"
src="ab93c009-bb7b-4291-b057-d44fdc6f9f86">

crates/ruff_server/src/server/api/requests/execute_command.rs

@@ -11,8 +11,9 @@ use lsp_server::ErrorCode;
 use lsp_types::{self as types, request as req};
 use serde::Deserialize;
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 enum Command {
+    Debug,
     Format,
     FixAll,
     OrganizeImports,
@@ -33,13 +34,24 @@ impl super::RequestHandler for ExecuteCommand {
 impl super::SyncRequestHandler for ExecuteCommand {
     fn run(
         session: &mut Session,
-        _notifier: client::Notifier,
+        notifier: client::Notifier,
         requester: &mut client::Requester,
         params: types::ExecuteCommandParams,
     ) -> server::Result<Option<serde_json::Value>> {
         let command =
             Command::from_str(&params.command).with_failure_code(ErrorCode::InvalidParams)?;
 
+        if command == Command::Debug {
+            let output = debug_information(session);
+            notifier
+                .notify::<types::notification::LogMessage>(types::LogMessageParams {
+                    message: output,
+                    typ: types::MessageType::INFO,
+                })
+                .with_failure_code(ErrorCode::InternalError)?;
+            return Ok(None);
+        }
+
         // check if we can apply a workspace edit
         if !session.resolved_client_capabilities().apply_edit {
             return Err(anyhow::anyhow!("Cannot execute the '{}' command: the client does not support `workspace/applyEdit`", command.label())).with_failure_code(ErrorCode::InternalError);
@@ -87,6 +99,9 @@ impl super::SyncRequestHandler for ExecuteCommand {
                         .set_fixes_for_document(fixes, snapshot.query().version())
                         .with_failure_code(ErrorCode::InternalError)?;
                 }
+                Command::Debug => {
+                    unreachable!("The debug command should have already been handled")
+                }
             }
         }
 
@@ -109,6 +124,7 @@ impl Command {
             Self::FixAll => "Fix all auto-fixable problems",
             Self::Format => "Format document",
             Self::OrganizeImports => "Format imports",
+            Self::Debug => "Print debug information",
         }
     }
 }
@@ -121,6 +137,7 @@ impl FromStr for Command {
             "ruff.applyAutofix" => Self::FixAll,
             "ruff.applyFormat" => Self::Format,
             "ruff.applyOrganizeImports" => Self::OrganizeImports,
+            "ruff.printDebugInformation" => Self::Debug,
             _ => return Err(anyhow::anyhow!("Invalid command `{name}`")),
         })
     }
@@ -148,3 +165,25 @@ fn apply_edit(
         },
     )
 }
+
+fn debug_information(session: &Session) -> String {
+    let executable = std::env::current_exe()
+        .map(|path| format!("{}", path.display()))
+        .unwrap_or_else(|_| "<unavailable>".to_string());
+    format!(
+        r#"executable = {executable}
+version = {version}
+encoding = {encoding:?}
+open_document_count = {doc_count}
+active_workspace_count = {workspace_count}
+configuration_files = {config_files:?}
+{client_capabilities}
+    "#,
+        version = crate::version(),
+        encoding = session.encoding(),
+        client_capabilities = session.resolved_client_capabilities(),
+        doc_count = session.num_documents(),
+        workspace_count = session.num_workspaces(),
+        config_files = session.list_config_files()
+    )
+}