[TrimmableTypeMap] Use Crc64 package naming by default with LowercaseCrc64 compatibility by Copilot · Pull Request #11193 · dotnet/android

Copilot · 2026-04-23T07:05:16Z

This updates trimmable type map generation to default to Crc64-based package naming for unregistered types, while preserving backwards compatibility for projects that explicitly set:

<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

Package naming policy support in trimmable typemap
- Wired AndroidPackageNamingPolicy into trimmable typemap generation.
- Added policy-aware hashing:
  - Crc64 (trimmable default) → crc64... using System.IO.Hashing.Crc64 with length mixing
  - LowercaseCrc64 → crc64... using the existing legacy/custom CRC64 implementation for compatibility with previous naming
- Removed trimmable XxHash64 handling, as it no longer provides value for this path.
- Kept Mono.Android namespace-preserving behavior unchanged.
Default policy update
- Crc64 is now the default only for trimmable typemap generation.
- The global AndroidPackageNamingPolicy default remains LowercaseCrc64 for non-trimmable typemap paths.
Hashing implementation refactor
- Moved scanner hashing logic out of JavaPeerScanner into a dedicated static ScannerHashingHelper for easier focused testing.
- Added dedicated ScannerHashingHelper.ToCrc64() for System.IO.Hashing.Crc64.
- Updated UTF-8 buffer handling for the fast Crc64 path to use stackalloc with new byte[N] fallback for larger buffers (>256 bytes).
- Added length mixing (crc64 ^ byteLength) in ToCrc64() to avoid equal outputs for different-length all-zero inputs.
- Kept legacy CRC64 compatibility behavior intact.
Targeted test updates
- Updated scanner expectations for crc64 trimmable defaults.
- Added coverage to verify:
  - default Crc64 output,
  - legacy LowercaseCrc64 compatibility output.
- Removed XxHash64-specific scanner expectations.
- Kept fixed-vector tests for legacy CRC64 known input/output pairs to validate backward compatibility behavior.
- Converted Crc64 known-output validation into a [Theory] with multiple input/output vectors.
- Added a regression test to ensure different-length zero-byte inputs produce different Crc64 outputs.
Related plumbing updates
- Passed package naming policy through the trimmable typemap target/task into TrimmableTypeMapGenerator and scanner hashing logic.
- Merged latest main conflict changes so trimmable typemap generation keeps both package naming policy support and MaxArrayRank plumbing.

return packageNamingPolicy switch {
	HashedPackageNamingPolicy.LowercaseCrc64 => "crc64" + ScannerHashingHelper.ToLegacyCrc64 (ns, assemblyName),
	HashedPackageNamingPolicy.Crc64 => "crc64" + ScannerHashingHelper.ToCrc64 (ns, assemblyName),
	_ => throw new InvalidOperationException ($"Unsupported package naming policy: {packageNamingPolicy}"),
};

simonrozsival · 2026-04-23T09:25:13Z

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

Copilot · 2026-04-23T09:57:50Z

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

Updated in 1049678: auto-generated TrimmableTypeMap package names now use the xx64 prefix (with XxHash64), and related unit/integration test expectations were updated accordingly.

jonathanpeppers

Note that there is the property:

<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

We will probably want to introduce a new one for XxHash64.

It is a slight breaking change, because people could have a hardcoded package name in a script for launching their main activity, etc.

So, I think what we did in some really old Xamarin.Android release, we changed the default but allowed projects to still use the old one.

simonrozsival · 2026-04-23T15:03:09Z

It is a slight breaking change, because people could have a hardcoded package name in a script for launching their main activity, etc.

So funny thing is that the CSC64 we have in our C++(or C#?) code and CSC64 that is in System.IO.Hashing produce different results. I decided to use the System.IO.Hashing one in the trimmable typemap so that would be a breaking change anyway. I will need to revisit this and try to make the LowercaseCrc64 option be consistent with previous naming. The scenario with launching a specific Activity makes sense.

simonrozsival · 2026-04-23T15:04:44Z

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 implementation that is in existing C# or C++ code used by the "llvm-ir" typemap

Copilot · 2026-04-23T15:41:11Z

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 imple...

Implemented in ec92067: trimmable typemap now respects AndroidPackageNamingPolicy, defaults to XxHash64, and uses the legacy custom CRC64 path when policy is LowercaseCrc64 for backwards compatibility.

Note that there is the property:
<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

...

Addressed in ec92067: added trimmable support for AndroidPackageNamingPolicy with a new default of XxHash64, while keeping LowercaseCrc64 compatibility via the existing legacy CRC64 implementation.

simonrozsival · 2026-04-24T07:41:28Z

+		var data = System.Text.Encoding.UTF8.GetBytes (value);
+		var hash = System.IO.Hashing.XxHash64.Hash (data);
+		return BitConverter.ToString (hash).Replace ("-", "").ToLowerInvariant ();


@copilot we should take inspiration from dotnet/android-tools#335 and avoid so many allocations here - use stackalloc where possible and non-allocating method overloads. Make sure to reuse the ToHexString method which is a lot more efficient than what we have right now. Also I don't think we need to hash UTF-8, we can simply do ReadOnlySpan<byte> utf16Bytes = MemoryMarshal.AsBytes(text.AsSpan()); , right? We hash a lot of strings during the build process, so let's make sure we don't unnecessarily slow down builds.

Implemented in 8d5709b: reduced allocations in JavaPeerScanner by switching to span-based hex formatting (with stackalloc), using non-allocating XxHash64.Hash(ReadOnlySpan<byte>, Span<byte>), and removing intermediate "{ns}:{assembly}" string allocations via pooled UTF-8 buffers. I kept UTF-8 input for hash compatibility with existing outputs/policies.

simonrozsival

@copilot address these comments

I want to move the hashing code from JavaPeerScanner to a separate static ScannerHashingHelper class which can be better tested. I want a test that will just simply validate some known inputs to some known outputs of the legacy crc64 algorithm to prove we're maintaining backwards compatibility.

simonrozsival · 2026-04-24T09:41:22Z

 		<AndroidVersionCodePattern Condition=" '$(AndroidUseLegacyVersionCode)' != 'True' And '$(AndroidVersionCodePattern)' == '' ">{abi}{versionCode:D5}</AndroidVersionCodePattern>
 		<AndroidResourceGeneratorTargetName>UpdateGeneratedFiles</AndroidResourceGeneratorTargetName>
 		<AndroidUseApkSigner Condition=" '$(AndroidUseApkSigner)' == '' ">True</AndroidUseApkSigner>
-		<AndroidPackageNamingPolicy Condition=" '$(AndroidPackageNamingPolicy)' == '' ">LowercaseCrc64</AndroidPackageNamingPolicy>


the XxHash64 should be the default just for the trimmable typemap

Addressed in 05cebc7: reverted the global AndroidPackageNamingPolicy default and scoped XxHash64 as the default specifically for trimmable typemap generation.

Copilot · 2026-04-24T10:20:12Z

@copilot address these comments

I want to move the hashing code from JavaPeerScanner to a separate static ScannerHashingHelper class which can be better tested. I want a test that will just simply va...

Implemented in 05cebc7: moved scanner hashing into ScannerHashingHelper and added fixed-vector tests that validate known legacy CRC64 outputs to lock backward compatibility behavior.

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 imple...

Handled in 05cebc7: trimmable typemap continues to respect explicit <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>, while using XxHash64 as the trimmable default and keeping the legacy custom CRC64 path for compatibility.

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

xx64 is used for the new hash-based default path, while crc64 remains only for explicit LowercaseCrc64 compatibility. Confirmed in 05cebc7.

simonrozsival · 2026-04-27T08:03:40Z

@copilot update the PR by pulling latest main and resolve conflicts

Copilot · 2026-04-27T08:35:52Z

@copilot update the PR by pulling latest main and resolve conflicts

Done in 3722fd9: pulled latest main, merged it into this branch, and resolved the conflict in Microsoft.Android.Sdk.TypeMap.Trimmable.targets.

simonrozsival · 2026-04-27T09:21:07Z

@copilot in dotnet/android-tools#338 we actually showed that System.IO.Hashing.Crc64 is faster than xxhash64. This PR will still be useful, but in a different way:

HashedPackageNamingPolicy.LowercaseCrc64 - the legacy Crc64 code for backwards compatibility
HashedPackageNamingPolicy.Crc64 - the much faster System.IO.Hashing.Crc64 implementation - new default for trimmable type map

Copilot · 2026-04-27T09:53:30Z

@copilot in dotnet/android-tools#338 we actually showed that System.IO.Hashing.Crc64 is faster than xxhash64. This PR will still be useful, but in a different way:

`Hash...

Done in e9ae72c. Trimmable default is now Crc64 (using System.IO.Hashing.Crc64), while LowercaseCrc64 remains the legacy custom CRC64 path for compatibility. I also kept explicit XxHash64 support and updated tests for all three policy behaviors.

jonathanpeppers · 2026-04-27T14:20:27Z

+		Span<byte> hash = stackalloc byte [8];
+		System.IO.Hashing.Crc64.Hash (utf8Buffer.Slice (0, bytesWritten), hash);
+		return ToHexString (hash, lowercase: true);


One problem is if you have "\0" and "\0\0\0\0" both with all zeros, then the crc value will be the same. Is that a problem here?

We XOR the length on this one:

dotnet/android-tools@9e9d063

Good catch. Addressed in 7aa55cd: ToCrc64() now XORs the byte length into the CRC64 value (matching the legacy collision-avoidance approach), and I added a regression test for different-length zero-byte inputs. No UI changes (screenshot N/A).

jonathanpeppers · 2026-04-27T14:20:56Z

 			int slash = javaName.IndexOf ('/');
 			if (slash > 0) {
-				return "crc64.../" + javaName.Substring (slash + 1);
+				return "hash.../" + javaName.Substring (slash + 1);


We prefixed crc64 so the algorithm was clear. Should we pick something less generic than hash?

Addressed in 7aa55cd: normalization keeps the explicit crc64.../ prefix, so we avoid a generic hash marker and keep the algorithm intent clear. No UI changes (screenshot N/A).

…efault Agent-Logs-Url: https://github.com/dotnet/android/sessions/a90e2abd-ca59-4b98-a498-64caa983b1d0 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

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…seCrc64 legacy Agent-Logs-Url: https://github.com/dotnet/android/sessions/fdb58e79-42f0-4d7d-8180-2b58c52ae3f8 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

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simonrozsival · 2026-05-07T16:17:14Z

@copilot resolve the merge conflicts in this pull request, also address review comments from Jon

…ixes Agent-Logs-Url: https://github.com/dotnet/android/sessions/6064358e-ab27-46b0-a022-bc0dfde2443a Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

Copilot · 2026-05-07T16:51:39Z

@copilot resolve the merge conflicts in this pull request, also address review comments from Jon

Done in 7aa55cd: I merged latest origin/main, resolved the conflicts in the trimmable typemap generator/task/targets files, and addressed Jon’s CRC64 review items. No UI changes (screenshot N/A).

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[TrimmableTypeMap] Use xxhash64 instead of crc64 at build time #11192

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Copilot AI changed the title ~~[WIP] Use xxhash64 instead of crc64 at build time~~ [TrimmableTypeMap] Use XxHash64 for auto-generated Java package hashing Apr 23, 2026

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Copilot AI changed the title ~~[TrimmableTypeMap] Use XxHash64 for auto-generated Java package hashing~~ [TrimmableTypeMap] Use XxHash64 package naming by default with LowercaseCrc64 compatibility Apr 23, 2026

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Copilot AI changed the title ~~[TrimmableTypeMap] Use XxHash64 package naming by default with LowercaseCrc64 compatibility~~ [TrimmableTypeMap] Use Crc64 package naming by default with LowercaseCrc64 compatibility Apr 27, 2026

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Comment thread tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Scanner/ScannerHashingHelperTests.cs

Comment thread src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerScanner.cs Outdated

Comment thread src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/ScannerHashingHelper.cs Outdated

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simonrozsival force-pushed the copilot/update-hash-algorithm-to-xxhash64 branch from ab689ec to d71cbd8 Compare May 4, 2026 18:37

Copilot AI and others added 6 commits May 4, 2026 20:39

[TrimmableTypeMap] support AndroidPackageNamingPolicy with XxHash64 d…

dadde19

…efault Agent-Logs-Url: https://github.com/dotnet/android/sessions/a90e2abd-ca59-4b98-a498-64caa983b1d0 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

[TrimmableTypeMap] reduce hashing allocations in JavaPeerScanner

679fa83

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[TrimmableTypeMap] extract scanner hashing helper and scope defaults

dc59600

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[TrimmableTypeMap] default trimmable policy to Crc64 and keep Lowerca…

554672d

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[TrimmableTypeMap] remove xxhash64 path and improve Crc64 hashing buf…

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[TrimmableTypeMap] clarify Crc64 switch and keep pooled legacy buffering

0354f0d

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simonrozsival force-pushed the copilot/update-hash-algorithm-to-xxhash64 branch from d71cbd8 to 0354f0d Compare May 4, 2026 18:41

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Merge origin/main and resolve TrimmableTypeMap conflicts with CRC64 f…

7aa55cd

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