[SR-1359] Android: ICU should be statically linked (and patch to make static linking possible)

[swift-ci]

Previous ID	SR-1359
Radar	None
Original Reporter	ewmailing (JIRA User)
Type	Improvement

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 1 | |Component/s | Compiler | |Labels | Improvement, Android, ICU | |Assignee | jblatecky (JIRA) | |Priority | Medium | md5: 57cffc55e2d8137ac432f00b13ecc676

Issue Description:

This merges with my prior FindICU.cmake general patch which allow for ICU to be
static libraries. (See https://bugs.swift.org/browse/SR-1358)

This change is needed for Android because dynamically linking libicu is
not reliable on Android. There are multiple problems:

• libICU is sometimes an internal/private component on Android. In some
  cases it appears that tryiing to LoadLibrary on libICU will silently
  skip because the OS already has one loaded. If the symbol names don't
  match, you get unresolved symbol errors at runtime resulting from a
  crash without a good understanding why. (This happened to me on my Nexus
  7 2013 with 5.0.2). And if the symbols match, but the versions are
  different, you may have even tougher problems.

• If your application needs ICU, you now run the risk of having
  conflicting versions of ICU. This is a particular risk for middleware
  where the user may have not built Swift themselves.

• Dealing with loading the ICU dependencies is annoying on Android
  because you must write Java code to load all the libraries, and in the
  correct order. And your build process must also be aware of all the
  dependencies so all the .so's get packaged.

So static linking ICU solves all these problems.

But additionally, the issue of linking the C++ standard library becomes
an issue. Again, there are similar issues with dynamically linking
because Android doesn't provide a pre-installed system-wide one we can
rely on. Additionally:

• Android actually provides 3 or 4 different C++ standard libraries you
  can pick from, all of which are incompatible with each other.

• Every new NDK release risks a new version of each of the standard
  libraries which breaks binary compatibility. If the user is just using
  the Swift compiler and doesn't think about these issues, this may cause
  hard problems.

• Also, statically linking ICU caused building command line executables
  (tests) to fail with unresolved symbols. Statically linking C++ fixes
  this problem and the original behavior is preserved.

So static linking solves these problems too.

Two new switches are needed to build for Android:
--android-icu-data-include /path/to/include
--android-icu-data /path/to/libicudata

My patch is here:
https://github.com/ewmailing/swift/commit/8af36d6c724abc52ba35fcd096acb571c5af0875

[swift-ci]

Comment by Amr Aboelela (JIRA)

I tried to link it statically to libswiftCore.so but it didn't work well.

[finagolfin]

The libicu dependency of the standard library was removed last month:

https://github.com/apple/swift/pull/40340