[JNIEnv] Support sbyte jagged arrays

[simonrozsival]

Summary

• add explicit sbyte converters beside the existing byte converters used by shared JNIEnv array creation, copying, reading, and element access
• reinterpret sbyte[] as JNI byte-array storage bit-for-bit, so negative managed values retain their two's-complement byte representation
• keep JNI [B fallback routing mapped to managed byte, avoiding any canonicalization of existing byte requests to sbyte

This affects generic and non-generic JNIEnv.NewArray, JNIEnv.GetArray, and JNIEnv.CopyArray paths, including recursive jagged-array handling.

Experiment evidence

Both legacy and trimmable typemap experiments produced the expected JNI signatures ([[B and [[[B) for sbyte jagged arrays. Creation then failed during recursive leaf conversion with:

Don't know how to convert type 'System.SByte' to an Android.Runtime.IJavaObject.

The signatures were therefore already correct; the shared converter dictionaries omitted sbyte while containing byte.

Tests

Added on-device regression coverage for generic and non-generic NewArray/GetArray/CopyArray at ranks 1, 2, and 3:

• sbyte: minimum, negative, zero, and maximum values
• byte: values with high bits set, confirming existing unsigned managed behavior remains unchanged
• JNI signatures asserted as [B, [[B, and [[[B

Validation:

• dotnet build src/Mono.Android/Mono.Android.csproj --no-restore ... — passed (15 existing warnings)
• device tests not run because this worktree has no locally built SDK; direct test-project compilation is blocked by missing Java.Interop reflection test types in the unprepared checkout

[simonrozsival]

/review

[github-actions]

✅ Android PR Reviewer completed successfully!

Generated by Android PR Reviewer for #12115

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Pull request overview

This PR aims to extend Android.Runtime.JNIEnv array marshaling to support sbyte (including jagged arrays) by treating managed sbyte[] as JNI byte[] ([B) storage bit-for-bit, and it adds on-device regression tests for array creation, reading, and copying at ranks 1–3.

Changes:

• Add sbyte handling to shared JNIEnv converter tables used by NewArray, GetArray, CopyArray, and element access.
• Add new on-device tests validating sbyte/byte jagged-array round-trips and expected JNI signatures ([B, [[B, [[[B).

Show a summary per file

File	Description
tests/Mono.Android-Tests/Mono.Android-Tests/Android.Runtime/JnienvArrayMarshaling.cs	Adds regression tests for sbyte jagged arrays and high-bit byte preservation across ranks 1–3.
src/Mono.Android/Android.Runtime/JNIEnv.cs	Introduces sbyte entries in marshaling/converter dictionaries used by array creation/copying/reading and element access.

Review details

Suppressed comments (4)

src/Mono.Android/Android.Runtime/JNIEnv.cs:934

• ❌ error JNI interop — (byte[])(object)(sbyte[])source will throw InvalidCastException at runtime; arrays of sbyte are not interchangeable with arrays of byte. This path needs a real conversion or an sbyte[]-aware JNI region helper instead of casting.

				{ typeof (sbyte),       (source, dest) => CopyArray ((byte[]) (object) (sbyte[]) source, dest) },

src/Mono.Android/Android.Runtime/JNIEnv.cs:1057

• ❌ error JNI interop — CopyArray (source, (byte[])(object)r) will throw InvalidCastException because r is an sbyte[]. This will break JNIEnv.GetArray<sbyte> and jagged-array recursion for sbyte.

				{ typeof (sbyte), (type, source, len) => {
					var r = new sbyte [len];
					CopyArray (source, (byte[]) (object) r);
					return r;

src/Mono.Android/Android.Runtime/JNIEnv.cs:1393

• ❌ error JNI interop — NewArray ((byte[])(object)(sbyte[])source) relies on an invalid runtime cast between sbyte[] and byte[]. This will throw and prevent creating JNI arrays from managed sbyte[].

				{ typeof (sbyte),         (source) => NewArray ((byte[]) (object) (sbyte[]) source) },

src/Mono.Android/Android.Runtime/JNIEnv.cs:1531

• ❌ error JNI interop — (byte[])(object)_value will throw InvalidCastException because _value is an sbyte[]. This breaks setting individual sbyte array elements (and any recursive array creation path that uses this dictionary).

				{ typeof (sbyte), (dest, index, value) => {
					var _value = new[]{(sbyte) value!};
					_SetByteArrayRegion (dest, index, _value.Length, (byte[]) (object) _value);
				} },

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Lite

[github-actions]

⚠️ Needs Changes

Findings: 0 errors · 0 warnings · 1 suggestion

The sbyte converter additions are otherwise consistent with the existing signed/unsigned primitive-array reinterpretation pattern, and the rank 1–3 round-trip tests verify both signed values and unchanged high-bit byte behavior. Please avoid introducing the new null-forgiving operator noted inline; the focused element-access coverage requested in the existing review thread would also complete coverage of the changed converter tables.

The latest dotnet-android build (#1562046) is still in progress with no failures reported so far, so the PR is not yet fully green.

Generated by Android PR Reviewer for #12115 · gpt56 · 100.7 AIC · ⌖ 8.98 AIC · ⊞ 25.7K
_{Comment /review to run again}

[github-actions]

🤖 💡 Nullable — This new entry introduces another null-forgiving operator even though value is declared object?. Please pattern-match it to an sbyte (and throw a contextual exception for null or the wrong type) before creating _value; that preserves the invariant instead of suppressing nullable analysis.

Rule: Never use the null-forgiving operator