Factorio provides a Debug Adapter for compatible tools in single-session mode on stdin/stdout when launched with the --dap command line argument.

The Debug Adapter supports a Launch request with the following arguments:

• factorioArgs :: array[string]? : Command line arguments for the debug session

• followSymlinks :: boolean? : Follow symlinks when emitting locations (stack traces, etc) (default: true)

• hookDebugConsole :: boolean? : Enable catching errors and breakpoints/stepping in code called from the Debug Console (Evaluate context="repl") (default: false)

• trace :: boolean? : Trace DAP messages to a dap-trace.log (default: false)

• tags :: Any? : Extra debug session tags, see also tags

For mod objects that appear in debug listing, the following optional metatable methods may be used to customize their display:

• __tostring(self) -> string : Called when the object appears as a value, to format it for inline display.

• __debugcounts(self) -> indexedVariables :: int32 , namedVariables :: int32 : Called when the object appears as a value, to estimate the size of this object's children, and enabled paged listing for large indexed objects. If either count is returned as 0, the client may skip listing that section entirely. If the indexed count is non-zero, the client may choose to request the values in pages. The Indexed count should indicate the highest index present, to properly range paged fetch windows, even if not all keys will be filled when fetched.

• __debugchildren(self, filters :: DebugVariablesFilter) -> array(DebugVariable) : Called when the object is expanded to list its children. If __debugcounts was implemented, the client may choose to fetch Indexed and Named children sections separately, and Indexed children in 0-based pages on-demand for display. If not all values in the requested page exist (such as a key 0), they may be omitted from output entirely. See also describe_field.

This class also provides debug session APIs, as the global object debugadapter in all stages.