Allow starting debug server without opening apps

README.md

@@ -138,7 +138,7 @@ d => 4
 [1, 2, 3, 4]
 ```
 
-### Invoke the program from the debugger as a traditional debuggers
+### Invoke the program from the debugger as a traditional debugger
 
 If you don't want to modify the source code, you can set breakpoints with a debug command `break` (`b` for short).
 Using `rdbg` command (or `bundle exec rdbg`) to launch the program without any modifications, you can run the program with the debugger.
@@ -253,7 +253,7 @@ Examples:
 * `rdbg -c -- bundle exec rake test`
 * `rdbg -c -- ruby target.rb` is same as `rdbg target.rb`
 
-NOTE: `--` is needed to separate the command line options for `rdbg` and invoking command. For example, `rdbg -c rake -T` is recognized like `rdbg -c -T -- rake`. It should be `rdbg -c -- rake -T`.
+NOTE: `--` is needed to separate the command line options for `rdbg` from the invoked command. For example, `rdbg -c rake -T` is recognized like `rdbg -c -T -- rake`. It should be `rdbg -c -- rake -T`.
 
 NOTE: If you want to use bundler (`bundle` command), you need to write `gem debug` line in your `Gemfile`.
 
@@ -358,15 +358,20 @@ $ RUBY_DEBUG_PORT=12345 ruby target.rb
 
 ### Integration with external debugger frontend
 
-You can attach with external debugger frontend with VSCode and Chrome.
+You can start a debugging session for an external debugger frontend using:
 
-```
+```shell
 $ rdbg --open=[frontend] target.rb
 ```
 
-will open a debug port and `[frontend]` can attach to the port.
+The currently available frontends are:
 
-Also `open` command allows opening the debug port.
+| Flag | Frontend |
+|------|----------|
+| <nobr>`--open=vscode`</nobr>  | Starts a DAP session and automatically opens Visual Studio Code. |
+| <nobr>`--open=dap`</nobr>     | Starts a debug adapter protocol (DAP) session, _without_ opening Visual Studio code. This allows for another DAP client to connect instead.
+| <nobr>`--open=chrome`</nobr>  | Starts a CDP session and automatically opens Chrome. |
+| <nobr>`--open=cdp`</nobr>     | Starts a Chrome debug protocol (CDP) session, _without_ opening Chrome. This allows for another CDP client to connect instead.
 
 #### VSCode integration
 

lib/debug/config.rb

@@ -324,7 +324,7 @@ def self.parse_argv argv
           when 'tcp'
             config[:open] = true
             config[:port] ||= 0
-          when 'vscode', 'chrome', 'cdp'
+          when 'vscode', 'dap', 'chrome', 'cdp'
             config[:open] = f&.downcase
           else
             raise "Unknown option for --open: #{f}"

lib/debug/server.rb

@@ -376,9 +376,9 @@ def after_fork_parent
       # do nothing
     end
 
-    def vscode_setup debug_port
+    def vscode_setup debug_port, launch_vscode: true
       require_relative 'server_dap'
-      UI_DAP.setup debug_port
+      UI_DAP.setup debug_port if launch_vscode
     end
   end
 
@@ -442,8 +442,10 @@ def accept
           case CONFIG[:open]
           when 'chrome'
             chrome_setup
+          when 'dap-server' # Start in Debug Adapter Protocol mode without launching Visual Studio Code
+            vscode_setup @local_addr.inspect_sockaddr, launch_vscode: false
           when 'vscode'
-            vscode_setup @local_addr.inspect_sockaddr
+            vscode_setup @local_addr.inspect_sockaddr, launch_vscode: true
           end
 
           Socket.accept_loop(socks) do |sock, client|
@@ -496,7 +498,12 @@ def accept
       end
 
       ::DEBUGGER__.warn "Debugger can attach via UNIX domain socket (#{@sock_path})"
-      vscode_setup @sock_path if CONFIG[:open] == 'vscode'
+      case CONFIG[:open]
+      when 'dap-server' # Start in Debug Adapter Protocol mode without launching Visual Studio Code
+        vscode_setup @sock_path, launch_vscode: false
+      when 'vscode'
+        vscode_setup @sock_path, launch_vscode: true
+      end
 
       begin
         Socket.unix_server_loop @sock_path do |sock, client|

lib/debug/session.rb

@@ -1118,9 +1118,15 @@ def register_default_command
         when 'vscode'
           CONFIG[:open] = 'vscode'
           ::DEBUGGER__.open nonstop: true
-        when 'chrome', 'cdp'
+        when 'dap'
+          CONFIG[:open] = 'dap'
+          ::DEBUGGER__.open nonstop: true
+        when 'chrome'
           CONFIG[:open] = 'chrome'
           ::DEBUGGER__.open_tcp host: CONFIG[:host], port: (CONFIG[:port] || 0), nonstop: true
+        when 'cdp'
+          CONFIG[:open] = 'cdp'
+          ::DEBUGGER__.open_tcp host: CONFIG[:host], port: (CONFIG[:port] || 0), nonstop: true
         else
           raise "Unknown arg: #{arg}"
         end

misc/README.md.erb

@@ -138,7 +138,7 @@ d => 4
 [1, 2, 3, 4]
 ```
 
-### Invoke the program from the debugger as a traditional debuggers
+### Invoke the program from the debugger as a traditional debugger
 
 If you don't want to modify the source code, you can set breakpoints with a debug command `break` (`b` for short).
 Using `rdbg` command (or `bundle exec rdbg`) to launch the program without any modifications, you can run the program with the debugger.
@@ -253,7 +253,7 @@ Examples:
 * `rdbg -c -- bundle exec rake test`
 * `rdbg -c -- ruby target.rb` is same as `rdbg target.rb`
 
-NOTE: `--` is needed to separate the command line options for `rdbg` and invoking command. For example, `rdbg -c rake -T` is recognized like `rdbg -c -T -- rake`. It should be `rdbg -c -- rake -T`.
+NOTE: `--` is needed to separate the command line options for `rdbg` from the invoked command. For example, `rdbg -c rake -T` is recognized like `rdbg -c -T -- rake`. It should be `rdbg -c -- rake -T`.
 
 NOTE: If you want to use bundler (`bundle` command), you need to write `gem debug` line in your `Gemfile`.
 
@@ -358,15 +358,20 @@ $ RUBY_DEBUG_PORT=12345 ruby target.rb
 
 ### Integration with external debugger frontend
 
-You can attach with external debugger frontend with VSCode and Chrome.
+You can start a debugging session for an external debugger frontend using:
 
-```
+```shell
 $ rdbg --open=[frontend] target.rb
 ```
 
-will open a debug port and `[frontend]` can attach to the port.
+The currently available frontends are:
 
-Also `open` command allows opening the debug port.
+| Flag | Frontend |
+|------|----------|
+| <nobr>`--open=vscode`</nobr>  | Starts a DAP session and automatically opens Visual Studio Code. |
+| <nobr>`--open=dap`</nobr>     | Starts a debug adapter protocol (DAP) session, _without_ opening Visual Studio code. This allows for another DAP client to connect instead.
+| <nobr>`--open=chrome`</nobr>  | Starts a CDP session and automatically opens Chrome. |
+| <nobr>`--open=cdp`</nobr>     | Starts a Chrome debug protocol (CDP) session, _without_ opening Chrome. This allows for another CDP client to connect instead.
 
 #### VSCode integration