Handling Static Linking with Different Versions of Abseil in Libraries

[mudream4869]

I noticed versioning in the symbol table of an LTS version (by nm). Does this mean that if two libraries are statically linked to different versions of Abseil and they don’t expose the Abseil API, our program can still statically link to both libraries without issues?

[derekmauro]

I believe you are asking about the inline namespaces. They are for handling this situation, though I'm not sure how well the mechanism has been tested in practice.

abseil-cpp/absl/base/options.h

Lines 206 to 229 in f7c22f5

	// ABSL_OPTION_USE_INLINE_NAMESPACE
	// ABSL_OPTION_INLINE_NAMESPACE_NAME
	//
	// These options controls whether all entities in the absl namespace are
	// contained within an inner inline namespace. This does not affect the
	// user-visible API of Abseil, but it changes the mangled names of all symbols.
	//
	// This can be useful as a version tag if you are distributing Abseil in
	// precompiled form. This will prevent a binary library build of Abseil with
	// one inline namespace being used with headers configured with a different
	// inline namespace name. Binary packagers are reminded that Abseil does not
	// guarantee any ABI stability in Abseil, so any update of Abseil or
	// configuration change in such a binary package should be combined with a
	// new, unique value for the inline namespace name.
	//
	// A value of 0 means not to use inline namespaces.
	//
	// A value of 1 means to use an inline namespace with the given name inside
	// namespace absl. If this is set, ABSL_OPTION_INLINE_NAMESPACE_NAME must also
	// be changed to a new, unique identifier name. In particular "head" is not
	// allowed.
	#define ABSL_OPTION_USE_INLINE_NAMESPACE 0
	#define ABSL_OPTION_INLINE_NAMESPACE_NAME head