Only export R_init_data_table

[aitap]

This will avoid name clashes between data.table functions (now hidden) and other functions in the global namespace visible to the shared library loader.

Tested on R-4.2/Linux, R-3.5/Windows.

Fixes: #7605

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (35dbf06) to head (1ecbe92).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7607   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          87       87           
  Lines       16896    16896           
=======================================
  Hits        16730    16730           
  Misses        166      166           

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[github-actions]

• HEAD=visibility-hidden slower P<0.001 for memrecycle regression fixed in #5463
  

Generated via commit 1ecbe92

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	5 minutes and 26 seconds
Installing different package versions	11 minutes and 7 seconds
Running and plotting the test cases	4 minutes and 6 seconds

[TysonStanley]

Looks like once this is merged and cherry-picked into the patch, we can submit 1.18.2. Thanks @aitap for getting a fix so quickly that we can include it in this submission.

[MichaelChirico]

Great! TIL about the win.def thing -- it's common elsewhere on CRAN though:

https://github.com/search?q=org%3Acran%20path%3A%2Fwin%5C.def%2F&type=code

Would you say it's worth reporting to other maintainers if they have visibility restricted but don't have this file?

e.g. {xml2}: r-lib/xml2@1ffdce4

[aitap]

I don't know whether the same problem is possible on Windows. On Linux (and other Unix-likes) a DLL can be linked with missing symbols and resolve them from the main process (or other DLLs) when it's loaded. That's how R works when compiled without --enable-R-shlib (and how LD_PRELOAD tricks work). On Windows linking is more explicit, specifying which DLL every symbol is imported from, so it should be much harder to link to the wrong function by accident.

Still, they do export all these functions on Windows:

$ /x86_64-w64-mingw32.static.posix/bin/objdump.exe -p R-4.5.1/library/xml2/libs/x64/xml2.dll
R-4.5.1/library/xml2/libs/x64/xml2.dll:     file format pei-x86-64
...
[Ordinal/Name Pointer] Table
        [   0] R_init_xml2
        [   1] _Z11getNodeTypeP7SEXPREC
        [   2] _Z14node_attr_implP7SEXPRECRKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES0_S0_
        [   3] _Z14node_name_implP7SEXPRECS0_
        [   4] _Z14node_path_implP7SEXPREC
        [   5] _Z14node_text_implP7SEXPREC
        [   6] _Z14node_type_implP7SEXPREC
        [   7] _Z15cache_namespaceP8_xmlNodeP5NsMap
        [   8] _Z15node_attrs_implP7SEXPRECS0_
        [   9] _Z15xmlAddNamespaceP8_xmlNodeP6_xmlNs
        [  10] _Z15xmlNsDefinitionP8_xmlNodePKh
...

(95 in total)

It wouldn't hurt to hide them.