5 files changed, 97 insertions, 21 deletions

diff --git a/.vscode/launch.json b/.vscode/launch.json
index 8ca27d878..021b8f048 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -120,6 +120,12 @@
       "sourceMaps": true,
       "outFiles": [ "${workspaceFolder}/editors/code/out/tests/unit/**/*.js" ],
       "preLaunchTask": "Pretest"
+    },
+    {
+      "name": "Win Attach to Server",
+      "type": "cppvsdbg",
+      "processId":"${command:pickProcess}",
+      "request": "attach"
     }
   ]
 }
diff --git a/crates/rust-analyzer/src/bin/args.rs b/crates/rust-analyzer/src/bin/args.rs
index 7d917946e..37d8414f4 100644
--- a/crates/rust-analyzer/src/bin/args.rs
+++ b/crates/rust-analyzer/src/bin/args.rs
@@ -14,7 +14,9 @@ use vfs::AbsPathBuf;
 pub(crate) struct Args {
     pub(crate) verbosity: Verbosity,
     pub(crate) log_file: Option<PathBuf>,
+    pub(crate) no_buffering: bool,
     pub(crate) command: Command,
+    pub(crate) wait_dbg: bool,
 }
 
 pub(crate) enum Command {
@@ -47,11 +49,17 @@ FLAGS:
     -vv, --spammy
     -q,  --quiet      Set verbosity
 
-    --log-file <PATH> Log to the specified filed instead of stderr
+    --log-file <PATH> Log to the specified file instead of stderr
+    --no-log-buffering
+                      Flush log records to the file immediately
+
+    --wait-dbg        Wait until a debugger is attached to.
+                      The flag is valid for debug builds only
 
 ENVIRONMENTAL VARIABLES:
     RA_LOG            Set log filter in env_logger format
     RA_PROFILE        Enable hierarchical profiler
+    RA_WAIT_DBG       If set acts like a --wait-dbg flag
 
 COMMANDS:
 
@@ -114,6 +122,8 @@ impl Args {
                 verbosity: Verbosity::Normal,
                 log_file: None,
                 command: Command::Version,
+                no_buffering: false,
+                wait_dbg: false,
             });
         }
 
@@ -130,21 +140,41 @@ impl Args {
             (false, true, true) => bail!("Invalid flags: -q conflicts with -v"),
         };
         let log_file = matches.opt_value_from_str("--log-file")?;
+        let no_buffering = matches.contains("--no-log-buffering");
+        let wait_dbg = matches.contains("--wait-dbg");
 
         if matches.contains(["-h", "--help"]) {
             eprintln!("{}", HELP);
-            return Ok(Args { verbosity, log_file: None, command: Command::Help });
+            return Ok(Args {
+                verbosity,
+                log_file: None,
+                command: Command::Help,
+                no_buffering,
+                wait_dbg,
+            });
         }
 
         if matches.contains("--print-config-schema") {
-            return Ok(Args { verbosity, log_file, command: Command::PrintConfigSchema });
+            return Ok(Args {
+                verbosity,
+                log_file,
+                command: Command::PrintConfigSchema,
+                no_buffering,
+                wait_dbg,
+            });
         }
 
         let subcommand = match matches.subcommand()? {
             Some(it) => it,
             None => {
                 finish_args(matches)?;
-                return Ok(Args { verbosity, log_file, command: Command::RunServer });
+                return Ok(Args {
+                    verbosity,
+                    log_file,
+                    command: Command::RunServer,
+                    no_buffering,
+                    wait_dbg,
+                });
             }
         };
         let command = match subcommand.as_str() {
@@ -219,11 +249,17 @@ impl Args {
             },
             _ => {
                 eprintln!("{}", HELP);
-                return Ok(Args { verbosity, log_file: None, command: Command::Help });
+                return Ok(Args {
+                    verbosity,
+                    log_file: None,
+                    command: Command::Help,
+                    no_buffering,
+                    wait_dbg,
+                });
             }
         };
         finish_args(matches)?;
-        Ok(Args { verbosity, log_file, command })
+        Ok(Args { verbosity, log_file, command, no_buffering, wait_dbg })
     }
 }
 
diff --git a/crates/rust-analyzer/src/bin/logger.rs b/crates/rust-analyzer/src/bin/logger.rs
index 3bcb1ae37..14887c5cc 100644
--- a/crates/rust-analyzer/src/bin/logger.rs
+++ b/crates/rust-analyzer/src/bin/logger.rs
@@ -4,7 +4,7 @@
 
 use std::{
     fs::File,
-    io::{BufWriter, Write},
+    io::{self, BufWriter, Write},
 };
 
 use env_logger::filter::{Builder, Filter};
@@ -14,10 +14,11 @@ use parking_lot::Mutex;
 pub(crate) struct Logger {
     filter: Filter,
     file: Option<Mutex<BufWriter<File>>>,
+    no_buffering: bool,
 }
 
 impl Logger {
-    pub(crate) fn new(log_file: Option<File>, filter: Option<&str>) -> Logger {
+    pub(crate) fn new(log_file: Option<File>, no_buffering: bool, filter: Option<&str>) -> Logger {
         let filter = {
             let mut builder = Builder::new();
             if let Some(filter) = filter {
@@ -28,7 +29,7 @@ impl Logger {
 
         let file = log_file.map(|it| Mutex::new(BufWriter::new(it)));
 
-        Logger { filter, file }
+        Logger { filter, file, no_buffering }
     }
 
     pub(crate) fn install(self) {
@@ -46,7 +47,8 @@ impl Log for Logger {
         if !self.filter.matches(record) {
             return;
         }
-        match &self.file {
+
+        let should_flush = match &self.file {
             Some(w) => {
                 let _ = writeln!(
                     w.lock(),
@@ -55,19 +57,32 @@ impl Log for Logger {
                     record.module_path().unwrap_or_default(),
                     record.args(),
                 );
+                self.no_buffering
+            }
+            None => {
+                eprintln!(
+                    "[{} {}] {}",
+                    record.level(),
+                    record.module_path().unwrap_or_default(),
+                    record.args(),
+                );
+                true // flush stderr unconditionally
             }
-            None => eprintln!(
-                "[{} {}] {}",
-                record.level(),
-                record.module_path().unwrap_or_default(),
-                record.args(),
-            ),
+        };
+
+        if should_flush {
+            self.flush();
         }
     }
 
     fn flush(&self) {
-        if let Some(w) = &self.file {
-            let _ = w.lock().flush();
+        match &self.file {
+            Some(w) => {
+                let _ = w.lock().flush();
+            }
+            None => {
+                let _ = io::stderr().flush();
+            }
         }
     }
 }
diff --git a/crates/rust-analyzer/src/bin/main.rs b/crates/rust-analyzer/src/bin/main.rs
index bee2eedbc..088b17b03 100644
--- a/crates/rust-analyzer/src/bin/main.rs
+++ b/crates/rust-analyzer/src/bin/main.rs
@@ -21,6 +21,7 @@ static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 
 fn main() {
     if let Err(err) = try_main() {
+        log::error!("Unexpected error: {}", err);
         eprintln!("{}", err);
         process::exit(101);
     }
@@ -28,7 +29,17 @@ fn main() {
 
 fn try_main() -> Result<()> {
     let args = args::Args::parse()?;
-    setup_logging(args.log_file)?;
+
+    #[cfg(debug_assertions)]
+    if args.wait_dbg || env::var("RA_WAIT_DBG").is_ok() {
+        #[allow(unused_mut)]
+        let mut d = 4;
+        while d == 4 {
+            d = 4;
+        }
+    }
+
+    setup_logging(args.log_file, args.no_buffering)?;
     match args.command {
         args::Command::RunServer => run_server()?,
         args::Command::PrintConfigSchema => {
@@ -56,7 +67,7 @@ fn try_main() -> Result<()> {
     Ok(())
 }
 
-fn setup_logging(log_file: Option<PathBuf>) -> Result<()> {
+fn setup_logging(log_file: Option<PathBuf>, no_buffering: bool) -> Result<()> {
     env::set_var("RUST_BACKTRACE", "short");
 
     let log_file = match log_file {
@@ -69,7 +80,7 @@ fn setup_logging(log_file: Option<PathBuf>) -> Result<()> {
         None => None,
     };
     let filter = env::var("RA_LOG").ok();
-    logger::Logger::new(log_file, filter.as_deref()).install();
+    logger::Logger::new(log_file, no_buffering, filter.as_deref()).install();
 
     tracing_setup::setup_tracing()?;
 
diff --git a/docs/dev/debugging.md b/docs/dev/debugging.md
index 8c48fd5a1..cc7a790ff 100644
--- a/docs/dev/debugging.md
+++ b/docs/dev/debugging.md
@@ -57,6 +57,14 @@ To apply changes to an already running debug process, press <kbd>Ctrl+Shift+P</k
 
 - Go back to the `[Extension Development Host]` instance and hover over a Rust variable and your breakpoint should hit.
 
+If you need to debug the server from the very beginning, including its initialization code, you can use the `--wait-dbg` command line argument or `RA_WAIT_DBG` environment variable. The server will spin at the beginning of the `try_main` function (see `crates\rust-analyzer\src\bin\main.rs`)
+```rust
+    let mut d = 4;
+    while d == 4 { // set a breakpoint here and change the value
+        d = 4;
+    }
+```
+
 ## Demo
 
 - [Debugging TypeScript VScode extension](https://www.youtube.com/watch?v=T-hvpK6s4wM).