Fix pointer array copying and various array pinning regressions in CoreCLR

[jkoritzinsky]

Summary

Fix copying and pinning regressions in CoreCLR's built-in array marshalling:

• Incorrect copying: the array metadata retained the pointee type while using a pointer-sized VARTYPE. The generic marshaler consequently used the pointee's size: a four-element byte*[] allocated and copied four bytes instead of 32 on x64.
• Lost pinning: the pinning predicate required a blittable value-type method table, excluding pointer and function-pointer type descriptors.
• Enum pinning: evaluate pinning against the enum's underlying primitive instead of the enum's own layout flags.
• Unicode character pinning: recognize char[] when its selected native representation is UTF-16, including explicit I2/U2 element types. ANSI and Boolean conversions continue to use copying.

Preserve the actual element TypeHandle in the marshalling operands, and select nint only as the carrier for generic copying. Managed allocation retains the declared pointer-array type and preserves null native arrays. Eligible forward P/Invokes use the existing pinning path; ref/out and reverse calls continue to copy.

Treat pointer elements as opaque native-sized values, including function pointers, struct pointers, and pointer-to-pointer elements. Update the managed compatibility assertions and native layout consumers accordingly. SAFEARRAY pointer support and non-pointer conversion rules are not broadened.

Regression coverage

Added 324 cases in the existing interop suites: 250 pointer/native-integer cases and 74 enum/character/conversion-control cases. Coverage includes forward P/Invoke and unmanaged-function-pointer delegates, required copying, exact copy-back array types, ref/out parameters, reverse callbacks, fixed-array fields, null/empty and odd-length arrays, and pinning across compacting GC. Pointer coverage includes float*, struct pointers, pointer-to-pointer elements, and managed/unmanaged function pointers.

The enum cases cover all eight standard underlying integral types. Character cases cover UTF-16, ANSI, and explicit element-type overrides; Boolean controls ensure conversion still occurs. Assertions distinguish passing managed contents directly from copying. Native exports and callback types explicitly use Cdecl for x86.

Validation

The product fixes and full 324-case regression set were validated locally:

Runtime configuration	New cases passed	Total related array cases passed
Windows x64 Checked	324	344
Windows x64 Release	324	344
Windows x86 Checked	324	343

The x86 difference is a 64-bit-only SAFEARRAY element-size mismatch control. Result XML was checked for failures, rather than relying only on the merged runner's exit code.

After the final test-only renames and runtime-specific data splits, the x64 Checked managed interop tests were rebuilt and rerun: 344 passed, 0 failed, including all 324 added cases. The Release and x86 results above precede those test-only changes.

Baseline copying, pinning, and function-pointer failures were reproduced. With only the copying repair applied, 80 copy cases passed while all four pinning-direction checks still failed, verifying that pinning does not merely hide a broken copy path.

The enum/character additions were also run before their fix: 32 pinning cases failed while all ANSI and Boolean conversion controls passed. All 74 added enum/character/control cases pass with the updated predicate.

IntPtr[] and UIntPtr[] already behaved correctly on this checkout; their product behavior is unchanged and is covered by the new tests.

Runtime-specific test exclusions

CI exposed separate NativeAOT and Mono issues; this PR does not change either runtime's implementation. Split theory data into passing and failing partitions and use narrowly scoped ActiveIssue attributes:

• NativeAOT: exclude exactly 27 failing rows: null fixed-array fields, null ref/out arrays, and nonempty reverse-copy cases. Tracked by [NativeAOT] Array marshalling differences exposed by pointer-array tests #134628; the remaining 223 pointer cases stay enabled.
• Compiled Mono: exclude exactly 17 failing function-pointer rows, tracked by [mono] Function pointer type equality and type compatibility are not properly handled #90308. Null function-pointer rows, ordinary data-pointer rows, and Mono interpreter function-pointer coverage remain enabled. Other method-level Mono exclusions for copying, layout, and character semantics remain.
• WebAssembly: retain the pointer-test exclusion for the shared test host's missing unmanaged-callback thunks, tracked by [wasm][coreclr] GetUnmanagedCallersOnlyThunk: unknown thunk for unmanaged callers only method #124219.

The newly excluded row sets match the recorded CI failures exactly, and the generated merged runner's predicates and skip reporting were checked. NativeAOT and Mono behavior was investigated from CI evidence and source inspection; neither runtime was rerun locally. Linux and ARM64 were not run locally.

Generated-code comparison

Release x64 P/Invoke stubs, with tiering and ReadyToRun disabled:

Direction	Baseline bytes	Fixed bytes	Baseline instructions	Fixed instructions
Default	294	185	86	58
In	294	185	86	58
Out	303	185	89	58
In/Out	332	185	97	58

The fixed pinning stubs contain no unmanaged-allocation helper, Memmove, or CoTaskMemFree calls. These are code-generation measurements, not benchmark timings.

For the new enum and UTF-16 declarations, Release x64 stubs shrink from 281-285 bytes (82-83 instructions) to 170 bytes (54 instructions), likewise eliminating allocation/copy/free calls. The ANSI and Boolean control stubs retain their previous code sizes and call paths.

Resolves #134174
Resolves #134576
Resolves #134577
Resolves #134575
Resolves #134573

Note

This PR was created with assistance from GitHub Copilot.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

CoreCLR IL stub and interop behavior changed substantially, with only Windows x86/x64 validation reported and Linux/ARM64 unverified.

Review effort: Lite
Findings: None

What changed in this PR

Fixes CoreCLR pointer-array marshalling by preserving pointer element types, using nint as the copy carrier, and enabling safe pinning.

Changes:

• Corrects native-size copying and declared array-type preservation.
• Enables pinning for pointer and function-pointer arrays.
• Adds extensive P/Invoke, reverse-callback, and fixed-array tests.

File	Description
mlinfo.h	Preserves the element TypeHandle.
mlinfo.cpp	Treats pointer elements as native-sized values.
ilmarshalers.cpp	Updates carrier selection, allocation, pinning, and layout handling.
fieldmarshaler.cpp	Uses the preserved element type for native layout.
StubHelpers.cs	Supports pointer-array compatibility assertions.
MarshalArrayLPArrayNative.cpp	Adds native pointer-array test helpers.
AsLPArrayTest.cs	Adds pointer-array marshalling and pinning coverage.
AsByValArrayTest.cs	Adds fixed pointer-array field coverage.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Broad, low-level CoreCLR marshalling changes require final human review.

Review effort: Lite
Findings: None

[Copilot]

Copilot review overview

🔵 Needs a closer look

The marshalling and runtime changes require final human review.

Review effort: Lite
Findings: None

[Copilot]

Copilot review overview

🟡 Changes recommended

One or more issues must be addressed before approval.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1 · 1

Open (2)

• Gate LPArray tests on Wasm reverse-thunk limitation · New
• Mark Wasm limitation with ActiveIssue instead of runtime skip · New

[jkoritzinsky]

Fixed the NativeAOT coverage and addressed the two new issues.

[Copilot]

Copilot review overview

🔵 Needs a closer look

The runtime marshalling changes are broad and require final human review.

Review effort: Lite
Findings: None

[Copilot]

Copilot review overview

🔵 Needs a closer look

Broad runtime marshalling changes and incomplete cross-platform validation warrant final human review.

Review effort: Lite
Findings: None

[MichalStrehovsky]

I'm not the one ultimately in charge, but this is starting to conflate fixes for things unrelated to pinning that will make backporting more difficult if we need to backport some of this.

[jkoritzinsky]

All of this PR needs to be back ported. I figured it was easier to backport 1 or 2 PRs that fix a bunch of regressions than 7 or 8 PRs with conflicting changes.