Memory leak in SWIG java wrappers

[s-rwe]

Description

We noticed an apparent memory leak when calling the SWIG Java wrappers, in our case namely for (repeated) calls to LGBM_BoosterSaveModelToStringSWIG. Doing so repeatedly keeps piling up more and more leaked memory, for each returned model string.

It seems that a patch with corresponding %newobject definitions in the swig interface (swig/lightgbmlib.i) fixes the issue and takes care of the necessary cleanup in the swig-generated code:

%newobject LGBM_BoosterSaveModelToStringSWIG;
%newobject LGBM_BoosterDumpModelSWIG;

Environment info

We are using the wrappers via https://github.com/metarank/lightgbm4j, which includes (in its latest version) LightGBM of v4.4.0. Using the latest release v4.6.0 instead doesn't change things, but the above %newobject declarations resolved the memory issues we're seeing.

[jameslamb]

Thanks for using LightGBM and for reporting this. We'd welcome a pull request!

[jameslamb]

I missed linking them together during PR review... this was fixed in #6923

[jameslamb]

Thanks again @s-rwe !