The Source tab specifies the source lookup paths for the debugger.

A launch configuration created by the project creation wizard includes the default lookup paths. These default paths are specified in the preferences () and apply to all projects created in the given workspace:

If the debugger fails to locate a readable file in all above paths, the debug session shows the “No source found for file” error message. To continue debugging, the user needs to locate the file manually.
By default, the debugger uses the first-found readable file as the source file. For the debugger to continue search on the path, select the Search for duplicate source files ... option.