Report FATAL_ERROR for macOS system libkrb5

[timwoj]

The version of libkrb5 that comes with macOS is quite old and has problems that cause Zeek's btests to fail. Instead of blindly using it, report an error and tell the user to use the version from Homebrew. That version is known to work.

[awelzel]

Nit, but also didn't test.

Suggested change

	string(FIND "${LibKrb5_LIBRARY}" "/Library/Developer/CommandLineTools/SDKs"
	if ( "${LibKrb5_LIBRARY}" MATCHES "..." )
	message(FATAL_ERROR)
	endif ()

I'm also wondering if there's a define or something in krb5.h that could be used for identifying the wrong/too-old version, but if what you have works 👍

[timwoj]

I'm also wondering if there's a define or something in krb5.h that could be used for identifying the wrong/too-old version, but if what you have works

I looked through it and couldn't find a version number or anything unforunately. The best indicator I could find of it being very old was simply the copyright information. I couldn't tell you what version Apple is actually including here without pulling all of the old tarballs and diffing. It's at least 12 years old, because krb5/krb5@17e2050 changed everything to use stdint.h types and Apple's version doesn't include that.

[timwoj]

Nit, but also didn't test.

string(FIND) is probably better here because the path changes as you install new versions of the macOS SDK:

/Library/Developer/CommandLineTools/SDKs/MacOSX13.3.sdk/usr/lib/libkrb5.tbd
/Library/Developer/CommandLineTools/SDKs/MacOSX14.4.sdk/usr/lib/libkrb5.tbd
/Library/Developer/CommandLineTools/SDKs/MacOSX14.5.sdk/usr/lib/libkrb5.tbd
/Library/Developer/CommandLineTools/SDKs/MacOSX15.4.sdk/usr/lib/libkrb5.tbd

I suppose it could match a regex. We definitely do if MATCHES more often than we do string(FIND).