E0004¶

Code: E0004
Message: No program specified to debug

No program was specified to debug.

When you start an IronPLC debug session, the launch configuration’s program attribute must point at the file to debug. This error appears when program is empty and there is no debuggable file active in the editor, so the debugger has nothing to launch.

The IronPLC debugger accepts two kinds of program: a Structured Text source file, which it compiles to a bytecode container before launching, or an already-compiled .iplc container, which it launches directly. Either way, the program attribute has to resolve to a real path on disk.

Solutions:

Set the program explicitly: In .vscode/launch.json, set program to the path of a Structured Text source, for example "program": "${workspaceFolder}/main.st". An explicit path is the most reliable choice because it does not depend on which editor is focused.
Debug the active file: Use "program": "${file}" and make sure the Structured Text file you want to debug is the focused editor when you press F5. Otherwise ${file} resolves to whatever else is focused — for example launch.json while you are editing it — and the debugger has no Structured Text program to run.
Open a source file first: If you started debugging from an empty configuration, open the .st file in the editor before launching so the debugger can fall back to it.

Think IronPLC is wrong about this?

If you believe this diagnostic is incorrect, open an issue on GitHub with a small sample that demonstrates the problem.