cmd/dap: server - always headless, target - always foregrounded (#2589)

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

Documentation/usage/dlv.md

@@ -41,7 +41,7 @@ Pass flags to the program you are debugging using `--`, for example:
 * [dlv attach](dlv_attach.md)	 - Attach to running process and begin debugging.
 * [dlv connect](dlv_connect.md)	 - Connect to a headless debug server.
 * [dlv core](dlv_core.md)	 - Examine a core dump.
-* [dlv dap](dlv_dap.md)	 - [EXPERIMENTAL] Starts a TCP server communicating via Debug Adaptor Protocol (DAP).
+* [dlv dap](dlv_dap.md)	 - [EXPERIMENTAL] Starts a headless TCP server communicating via Debug Adaptor Protocol (DAP).
 * [dlv debug](dlv_debug.md)	 - Compile and begin debugging main package in current directory, or the package specified.
 * [dlv exec](dlv_exec.md)	 - Execute a precompiled binary, and begin a debug session.
 * [dlv replay](dlv_replay.md)	 - Replays a rr trace.

Documentation/usage/dlv_dap.md

 ## dlv dap
 
-[EXPERIMENTAL] Starts a TCP server communicating via Debug Adaptor Protocol (DAP).
+[EXPERIMENTAL] Starts a headless TCP server communicating via Debug Adaptor Protocol (DAP).
 
 ### Synopsis
 
 
-[EXPERIMENTAL] Starts a TCP server communicating via Debug Adaptor Protocol (DAP).
+[EXPERIMENTAL] Starts a headless TCP server communicating via Debug Adaptor Protocol (DAP).
 
-The server is headless and requires a DAP client like vscode to connect and request a binary
+The server is always headless and requires a DAP client like vscode to connect and request a binary
 to be launched or process to be attached to. The following modes are supported:
 - launch + exec (executes precompiled binary, like 'dlv exec')
 - launch + debug (builds and launches, like 'dlv debug')

cmd/dlv/cmds/commands.go

@@ -174,10 +174,10 @@ option to let the process continue or kill it.
 	// 'dap' subcommand.
 	dapCommand := &cobra.Command{
 		Use:   "dap",
-		Short: "[EXPERIMENTAL] Starts a TCP server communicating via Debug Adaptor Protocol (DAP).",
-		Long: `[EXPERIMENTAL] Starts a TCP server communicating via Debug Adaptor Protocol (DAP).
+		Short: "[EXPERIMENTAL] Starts a headless TCP server communicating via Debug Adaptor Protocol (DAP).",
+		Long: `[EXPERIMENTAL] Starts a headless TCP server communicating via Debug Adaptor Protocol (DAP).
 
-The server is headless and requires a DAP client like vscode to connect and request a binary
+The server is always headless and requires a DAP client like vscode to connect and request a binary
 to be launched or process to be attached to. The following modes are supported:
 - launch + exec (executes precompiled binary, like 'dlv exec')
 - launch + debug (builds and launches, like 'dlv debug')
@@ -188,6 +188,7 @@ While --continue is not supported, stopOnEntry launch/attach attribute can be us
 execution is resumed at the start of the debug session.`,
 		Run: dapCmd,
 	}
+	// TODO(polina): support --tty when dlv dap allows to launch a program from command-line
 	rootCommand.AddCommand(dapCommand)
 
 	// 'debug' subcommand.
@@ -409,7 +410,7 @@ func dapCmd(cmd *cobra.Command, args []string) {
 		}
 		defer logflags.Close()
 
-		if headless {
+		if cmd.Flag("headless").Changed {
 			fmt.Fprintf(os.Stderr, "Warning: dap mode is always headless\n")
 		}
 		if acceptMulti {
@@ -446,10 +447,9 @@ func dapCmd(cmd *cobra.Command, args []string) {
 			DisconnectChan: disconnectChan,
 			Debugger: debugger.Config{
 				Backend:              backend,
-				Foreground:           headless && tty == "",
+				Foreground:           true, // server always runs without terminal client
 				DebugInfoDirectories: conf.DebugInfoDirectories,
 				CheckGoVersion:       checkGoVersion,
-				TTY:                  tty,
 			},
 			CheckLocalConnUser: checkLocalConnUser,
 		})