Add RA_WAIT_DBG and docs

Author: vsrs

crates/rust-analyzer/src/bin/args.rs

@@ -57,6 +57,7 @@ FLAGS:
 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:
 

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

@@ -29,7 +29,7 @@ fn main() {
 
 fn try_main() -> Result<()> {
     let args = args::Args::parse()?;
-    if args.wait_dbg {
+    if args.wait_dbg || env::var("RA_WAIT_DBG").is_ok() {
         #[allow(unused_mut)]
         let mut d = 4;
         while d == 4 {

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).