TIFF_LIBRARIES are private

[dg0yt]

The public linkage of TIFF_LIBRARIES exposes TIFF to downstream compilation stages, even when linking to the shared libgeotiff. This isn't needed, and the exposure of TIFF::TIFF in dynamic builds is not handled in the exported CMake config.

[dg0yt]

FTR this bug was discovered in dynamic builds of PDAL 2.4 with GDAL 3.5.0rc2 CMake builds.

[hobu]

The linkages for the applications will need to be adjusted in support of this change too.

[rouault]

The linkages for the applications will need to be adjusted in support of this change too.

what do you mean exactly ?

[rouault]

hum actually I'm wondering if this change is correct. libtiff is a public dependency of libgeotiff because of the xtiffio.h header

[hobu]

    Creating library D:/a/libgeotiff/libgeotiff/libgeotiff/build/lib/Release/makegeo.lib and object D:/a/libgeotiff/libgeotiff/libgeotiff/build/lib/Release/makegeo.exp
makegeo.obj : error LNK2019: unresolved external symbol TIFFClose referenced in function main [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2001: unresolved external symbol TIFFClose [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
makegeo.obj : error LNK2019: unresolved external symbol TIFFSetField referenced in function SetUpTIFFDirectory [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
makegeo.obj : error LNK2019: unresolved external symbol TIFFWriteScanline referenced in function WriteImage [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
makegeo.obj : error LNK2019: unresolved external symbol TIFFError referenced in function WriteImage [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2019: unresolved external symbol TIFFOpen referenced in function XTIFFOpen [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2019: unresolved external symbol TIFFFdOpen referenced in function XTIFFFdOpen [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2019: unresolved external symbol TIFFClientOpen referenced in function XTIFFClientOpen [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2019: unresolved external symbol TIFFSetTagExtender referenced in function XTIFFClientOpen [D:\a\libgeotiff\libgeotiff\libgeotiff\build\bin\makegeo.vcxproj]
xtiff.lib(xtiff.obj) : error LNK2019: unresolved external symbol TIFFMergeFieldInfo referenced in function 

libtiff is a public dependency of libgeotiff because of the xtiffio.h

It would be nice to vendor that into libgeotiff. PDAL's kind of special though as we're one of the few direct users of external libgeotiff AND GDAL, but this has been annoyance.

[dg0yt]

Well, of course it is possible to stay with PUBLIC, but then it takes another change to the exported CMake config.

[dg0yt]

PDAL's kind of special though as we're one of the few direct users of external libgeotiff AND GDAL, but this has been annoyance.

It is not a PDAL issue but a libgeotiff issue:

• With public linkage, there is TIFF::TIFF in its INTERFACE_LINK_LIBRARIES, so it needs a find_dependency(TIFF) even for dynamic linkage. The target will provide the include path for TIFF.
• With private linkage, there is $<LINK_ONLY:TIFF::TIFF> in its INTERFACE_LINK_LIBRARIES, so it needs a find_dependency(TIFF) only for static linking to TIFF. The user must supply the include path for TIFF.

Given the header dependency, it must be PUBLIC instead.

[abellgithub]

@hobu asked for my comment.

It's not clear to me what the actual complaint is -- whether this is about symbol visibility from a DLL or simply about link-time requirements for downstream libraries.

If you really don't want the tiff symbols visible from the GDAL DSO, you need to change their visibility when building that shared library. Changing the PUBLIC/PRIVATE interface in cmake won't fix this. Like Windows, where you must explicitly choose the functions you want exported from a DLL interface, the same can be done on Linux by using __attribute__((visibility("default")) or __declspec(dllexport) along with setting default visibility to hidden when compiling. See here

Since PDAL was mentioned, I'll note that I'm almost finished with limiting symbol visibility from PDAL with this technique and I would think it would be in the next release.

[dg0yt]

Hm, another project asking for vcpkg updates?

[dg0yt]

We seem to post in parallel. But there is no hurry. I can prepare another, tested PR later tonight (CEST).

[rouault]

superseded per #77