Command line debugger enters infinite loop on Ctrl+D (end of transmission) character

[lihop]

Godot version

3.3.2-stable

System information

NixOS 21.11

Issue description

Typing Ctrl+D at CLI debugger prompt results in an infinite loop which also starts filling the log file at .local/share/godot/app_userdata/<project>/logs/godot.log with a string of the following format (script path being project dependent):

Debugger Break, Reason: 'Breakpoint'
*Frame 0 - res://drag_drop_script.gd:4 in function 'get_drag_data'
Enter "help" for assistance.
debug> 

Expected behavior:
I would expect Ctrl+D to exit the debugger which, on Linux atleast, is consistent with other REPLs/shells such as bash, python, node, and gdb.
At the very least, I would not expect the command line debugger to go into an infinite loop.

Steps to reproduce

1. Open any Godot project with a runnable main scene.
2. Start godot cli in debug mode godot -d.
3. Type Ctrl+C to drop to debugger prompt.
4. Type Ctrl+D.

Minimal reproduction project

No response

[lihop]

I did some digging and here is what I found:

Affected platforms

I cannot reproduce this issue on Windows.

On Windows, using the python repl for reference, I wasn't able to reproduce this issue in powershell or git-bash. The windows equivalent of Ctrl+D is Ctrl+Z (to exit python you can use Ctrl+Z + return). This had no effect on the command line debugger. In git-bash Ctrl+C and Ctrl+Z don't appear to work at all, either when using the command line debugger or python.

Causes

The debugger repl runs a while(true) loop that starts by calling OS::get_stdin_string() to get input from stdin:

godot/core/script_debugger_local.cpp

Lines 53 to 57 in 7610409

	while (true) {
	OS::get_singleton()->print("debug> ");
	String line = OS::get_singleton()->get_stdin_string().strip_edges();

OS::get_stdin_string() in turn calls fgets():

godot/drivers/unix/os_unix.cpp

Lines 149 to 159 in 7610409

	String OS_Unix::get_stdin_string(bool p_block) {
	if (p_block) {
	char buff[1024];
	String ret = stdin_buf + fgets(buff, 1024, stdin);
	stdin_buf = "";
	return ret;
	}
	return "";
	}

In the case of Ctrl+C, fgets() returns NULL and sets the error indicator for stdin to 1 (Interrupted system call).
In the case of Ctrl+D, fgets() returns NULL and sets the end-of-File indicator for stdin.
In both cases OS::get_stdin_string() returns empty string.

However, after encountering EOF, any subsequent calls to fgets() will immediately return NULL (without waiting for or reading any more user input), thus the command line debugger enters an infinite loop, repeating the line == "" case:

godot/core/script_debugger_local.cpp

Lines 61 to 65 in 7610409

	if (line == "") {
	print_line("\nDebugger Break, Reason: '" + p_script->debug_get_error() + "'");
	print_line("*Frame " + itos(current_frame) + " - " + p_script->debug_get_stack_level_source(current_frame) + ":" + itos(p_script->debug_get_stack_level_line(current_frame)) + " in function '" + p_script->debug_get_stack_level_function(current_frame) + "'");
	print_line("Enter \"help\" for assistance.");
	} else if (line == "c" || line == "continue")

Possible solutions

This patch to 3.3.2-stable (tested on linux) will cause the debugger to exit on Ctrl+D (on *nix platforms). It also changes the behavior of the debugger to exit on Ctrl+C (on *nix and presumably windows platforms) which would resolve #19775 if this is the desired behavior:

diff --git a/core/script_debugger_local.cpp b/core/script_debugger_local.cpp
index 3cc14daf4c..7ccec46033 100644
--- a/core/script_debugger_local.cpp
+++ b/core/script_debugger_local.cpp
@@ -53,7 +53,14 @@ void ScriptDebuggerLocal::debug(ScriptLanguage *p_script, bool p_can_continue, b
 	while (true) {
 
 		OS::get_singleton()->print("debug> ");
-		String line = OS::get_singleton()->get_stdin_string().strip_edges();
+		String line = OS::get_singleton()->get_stdin_string();
+
+		if (line == "") {
+			print_line("");
+			line = "quit";
+		} else {
+			line = line.strip_edges();
+		}
 
 		// Cache options
 		String variable_prefix = options["variable_prefix"];

[Xrayez]

I stumbled upon this as well in the past. I run tests using GitHub Actions in https://github.com/goostengine/goost/blob/2cf40249f90d198bf722002bf883f78fd93bbc72/.github/workflows/linux_builds.yml#L265-L267, and sometimes in case of script error the job keeps hanging for hours until the job finally stops. This also may produce huge logs files there, but looks like GitHub handles these kind of cases and cancels the job eventually.

[rcorre]

This patch to 3.3.2-stable (tested on linux) will cause the debugger to exit on Ctrl+D (on *nix platforms). It also changes the behavior of the debugger to exit on Ctrl+C (on *nix and presumably windows platforms) which would resolve #19775 if this is the desired behavior:

IMHO ctrl+c currently behaves correctly (though this is debated at #19775). However, the current behavior of ctrl+d is pretty clearly wrong.
Would there be any objection to a patch just fixing ctrl+d to exit the debugger instead of loop infinitely, but leaving ctrl+c as-is?