Long lived application data typically should not contain any thunks. This library can be used to examine values for unexpected thunks, which can then be used in assertions. This can be invaluable in avoiding memory leaks, or tracking down existing ones.
See my presentation MuniHac 2020: Being lazy without being bloated for an overview, motivating the library and explaining how it is intended to be used and how it works internally.
nothunks will try to get source information from info tables. For that one
needs to use GHC 9.2 or newer and compile the code with
-finfo-table-map. More precise information will be available if
-fdistinct-constructor-tables flag is used as well.