Review SDK size: consider IL stripping

[bruno-garcia]

We've received user feedback that the SDK is causing a significant increase of the final .apk.

[bitsandfoxes]

Using Unity 6.0.43 I've come up with the following comparison when targeting Android:

| Variant                      | APK Size   | Extracted  | lib/       | res/      | smali/     | assets/   |
|:-----------------------------|:-----------|:-----------|:-----------|:----------|:-----------|:----------|
| test_with_sentry             |  19.56 MB  |  80.20 MB  |  52.18 MB  |  6.51 KB  |  18.34 MB  |  9.62 MB  |
| └─ arm64-v8a                 |            |            |            |           |            |           |
|    ├─ libil2cpp.so           |            |  37.90 MB  |            |           |            |           |
|    ├─ libmain.so             |            |   6.54 KB  |            |           |            |           |
|    ├─ libsentry-android.so   |            |  15.60 KB  |            |           |            |           |
|    ├─ libsentry.so           |            |   1.17 MB  |            |           |            |           |
|    └─ libunity.so            |            |  13.08 MB  |            |           |            |           |
| test_without_android_sdk     |  18.82 MB  |  72.96 MB  |  51.00 MB  |  6.51 KB  |  12.29 MB  |  9.62 MB  |
| └─ arm64-v8a                 |            |            |            |           |            |           |
|    ├─ libil2cpp.so           |            |  37.90 MB  |            |           |            |           |
|    ├─ libmain.so             |            |   6.54 KB  |            |           |            |           |
|    └─ libunity.so            |            |  13.08 MB  |            |           |            |           |
| test_without_sentry          |  15.14 MB  |  60.47 MB  |  40.36 MB  |  6.51 KB  |  12.29 MB  |  7.77 MB  |
| └─ arm64-v8a                 |            |            |            |           |            |           |
|    ├─ libil2cpp.so           |            |  28.21 MB  |            |           |            |           |
|    ├─ libmain.so             |            |   6.54 KB  |            |           |            |           |
|    └─ libunity.so            |            |  12.14 MB  |            |           |            |           |

Comparing the .apks, adding Sentry increases the size by ~4.42MB. A big contributer is the libil2cpp.so, which could be affected by changes to code stripping settings that we're preventing here:

sentry-unity/package-dev/Runtime/SentryInitialization.cs

Line 38 in 1e1c853

[assembly: AlwaysLinkAssembly]

The increase in assets happens in assets/bin/Data/Managed/Metadata/global-metadata.dat.
The increase in smali happens in smali/io.sentry/.

[bruno-garcia]

@bitsandfoxes said:

I think my comment on AlwaysLinkAssembly preventing code stripping is wrong/misleading. The attribute forces the linker to search the assembly and makes the stripper treat it as if it has been marked as root.
So code stripping should still take effect and do its thing.

[bitsandfoxes]

In the table we see that the Android SDK does not actually add "that" much to the bundle size. I think I've narrowed down where the unexpected increase in size in libil2cpp.so is coming from.

Since there is limited dependency resolution for Unity packages, the SDK "deeply renames" its dependencies using a tool called "Assembly Alias". You can read more about how and why here.

But this means that in addition to the Unity/.NET SDK, C++ code gets generated for all its dependencies as well. Even if Unity or some other package would already bring them along.

We're now also setting the stripping level to High in CI for all Unity versions newer than 2019.