minor: Break out of waiting for debugger on Windows using native debugger check API.

For Windows, this removes the need to add a breakpoint and modify a value to exit the debugger wait loop.

As a ridealong, this adds a 100ms sleep for all platforms such that waiting for the debugger doesn't hog the CPU thread.

Author: PrototypeNM1

src/tools/rust-analyzer/crates/rust-analyzer/Cargo.toml

@@ -75,7 +75,7 @@ vfs.workspace = true
 paths.workspace = true
 
 [target.'cfg(windows)'.dependencies]
-windows-sys = { version = "0.52", features = ["Win32_System_Threading"] }
+windows-sys = { version = "0.52", features = ["Win32_System_Diagnostics_Debug", "Win32_System_Threading"] }
 
 [target.'cfg(not(target_env = "msvc"))'.dependencies]
 jemallocator = { version = "0.5.0", package = "tikv-jemallocator", optional = true }

src/tools/rust-analyzer/crates/rust-analyzer/src/bin/main.rs

@@ -10,7 +10,7 @@ extern crate rustc_driver as _;
 
 mod rustc_wrapper;
 
-use std::{env, fs, path::PathBuf, process::ExitCode, sync::Arc};
+use std::{env, fs, path::PathBuf, process::ExitCode, sync::Arc, thread::sleep};
 
 use anyhow::Context;
 use lsp_server::Connection;
@@ -44,11 +44,7 @@ fn actual_main() -> anyhow::Result<ExitCode> {
 
     #[cfg(debug_assertions)]
     if flags.wait_dbg || env::var("RA_WAIT_DBG").is_ok() {
-        #[allow(unused_mut)]
-        let mut d = 4;
-        while d == 4 {
-            d = 4;
-        }
+        wait_for_debugger();
     }
 
     if let Err(e) = setup_logging(flags.log_file.clone()) {
@@ -96,6 +92,28 @@ fn actual_main() -> anyhow::Result<ExitCode> {
     Ok(ExitCode::SUCCESS)
 }
 
+#[cfg(debug_assertions)]
+fn wait_for_debugger() {
+    #[cfg(target_os = "windows")]
+    {
+        use windows_sys::Win32::System::Diagnostics::Debug::IsDebuggerPresent;
+        // SAFETY: WinAPI generated code that is defensively marked `unsafe` but
+        // in practice can not be used in an unsafe way.
+        while unsafe { IsDebuggerPresent() } == 0 {
+            sleep(std::time::Duration::from_millis(100));
+        }
+    }
+    #[cfg(not(target_os = "windows"))]
+    {
+        #[allow(unused_mut)]
+        let mut d = 4;
+        while d == 4 {
+            d = 4;
+            sleep(std::time::Duration::from_millis(100));
+        }
+    }
+}
+
 fn setup_logging(log_file_flag: Option<PathBuf>) -> anyhow::Result<()> {
     if cfg!(windows) {
         // This is required so that windows finds our pdb that is placed right beside the exe.