add a TODO since this issue is eventually fixed

R/onLoad.R

@@ -24,6 +24,7 @@
     if (dllV != RV) {
       dll = if (.Platform$OS.type=="windows") "dll" else "so"
       # https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17478
+      # TODO(R>=4.0.0): Remove or adjust this message once we're sure all users are unaffected
       stopf("The data_table.%s version (%s) does not match the package (%s). Please close all R sessions to release the old %s and reinstall data.table in a fresh R session. Prior to R version 3.6.0 patched, R's package installer could leave a package in an apparently functional state where new R code was calling old C code silently: https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17478. Once a package is in this mismatch state it may produce wrong results silently until you next upgrade the package. This mismatch between R and C code can happen with any package not just data.table. It is just that data.table has added this check.", dll, dllV, RV, toupper(dll))
     }
     builtPath = system.file("Meta", "package.rds", package="data.table")