Delete ArrayEEClass - compute multidim array rank from BaseSize

[Copilot]

ArrayEEClass (ArrayClass) stored only m_rank — a single byte redundant with information already encoded in MethodTable::m_baseSize. This PR removes the class entirely and derives rank from BaseSize, matching NativeAOT's approach.

Changes

CoreCLR VM (C++)

• class.h: Remove ArrayClass entirely. Remove PTR_ArrayClass typedef (no longer needed). Add Module::CreateArrayMethodTable as friend of EEClass (its constructor is protected, and the function now calls ::new (pMemory) EEClass() directly).
• methodtable.inl: MethodTable::GetRank() now computes rank from BaseSize:

  // SZARRAY fast path unchanged; multidim:
  DWORD boundsSize = GetBaseSize() - ARRAYBASE_BASESIZE;
  return boundsSize / (sizeof(DWORD) * 2);

  This works because CreateArrayMethodTable sets BaseSize = ARRAYBASE_BASESIZE + Rank * sizeof(DWORD) * 2 for ELEMENT_TYPE_ARRAY. The DATA_ALIGNMENT > 4 padding path on 32-bit is dead code on all supported platforms.
• array.cpp: GenerateArrayAccessorCallSig and InitArrayMethodDesc become local static void functions (were ArrayClass members). Allocation uses sizeof(EEClass) and EEClass* directly; SetRank() call removed.
• object.inl: GetLowerBoundsOffset uses pMT->GetRank() directly.
• datadescriptor.inc: Remove ArrayClass type block; add CDAC_GLOBAL(ArrayBaseSize, uint32, ARRAYBASE_BASESIZE).
• methodtable.cpp: Remove redundant if (IsArray()) DAC memory enumeration block (now handled uniformly by EEClass::EnumMemoryRegions). Simplify array cast check to use !pTargetMT->IsMultiDimArray() instead of GetInternalCorElementType() == ELEMENT_TYPE_SZARRAY.
• methodtable.h, ceeload.h: Delete all friend class NativeImageDumper; declarations throughout the repo (4 occurrences).

Managed cDAC

• Remove DataType.ArrayClass, Data.ArrayClass.
• RuntimeTypeSystem_1.IsArray() computes rank from BaseSize using the new ArrayBaseSize global (Constants.Globals.ArrayBaseSize).

cDAC Tests

• Mock descriptors no longer allocate ArrayClass; multidim array MethodTable mock now sets BaseSize = ArrayBaseSize + rank * 2 * sizeof(int) (previously always used ArrayBaseSize, which was inconsistent with the real runtime).
• ObjectTests data-pointer assertions updated: for a rank-R multidim array, data starts at address + ArrayBaseSize + R * 2 * sizeof(int).
• Added ValidateMultidimArrayRank test (as a [Theory] over all standard architectures) directly verifying IsArray() returns correct rank (4 and 1) from BaseSize.

Documentation

• docs/design/datacontracts/RuntimeTypeSystem.md: Removed the ArrayClass | Rank data descriptor row, added ArrayBaseSize to the globals table, and updated the IsArray pseudocode to derive multidimensional array rank from BaseSize instead of reading from ArrayClass.

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[jkotas]

@copilot

[jkotas]

@copilot More feedback above

[jkotas]

@max-charlamb PTLA - small data contract simplification that makes NativeAOT and CoreCLR more similar.

Also, could you please take look at the runtime-diagnostics failures? They do not appear related to my change.

[Copilot]

Pull request overview

Removes the redundant CoreCLR ArrayClass/ArrayEEClass (which only stored array rank) and derives multidimensional array rank from MethodTable::BaseSize, aligning CoreCLR with the existing NativeAOT approach. Updates cDAC (native + managed) and its tests to match the new layout/contract shape.

Changes:

• CoreCLR VM: delete ArrayClass, refactor array helper methods to file-local statics, and compute MethodTable::GetRank() from BaseSize.
• cDAC: remove ArrayClass data/type usage and compute array rank from BaseSize (plus a new exported global for ARRAYBASE_BASESIZE).
• Tests: adjust mock descriptors/object layout math and add coverage validating multidim rank derivation.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/vm/array.cpp	Refactors former ArrayClass helpers to static functions; allocates EEClass directly for arrays.
src/coreclr/vm/class.h	Removes ArrayClass definition; adds Module::CreateArrayMethodTable friend to allow placement-new EEClass.
src/coreclr/vm/classcompat.h	Removes ArrayClass forward decl.
src/coreclr/vm/ceeload.h	Removes NativeImageDumper friend declarations.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Removes ArrayClass type; adds ArrayBaseSize global exporting ARRAYBASE_BASESIZE.
src/coreclr/vm/methodtable.cpp	Simplifies array casting logic and DAC memory enumeration now that ArrayClass is gone.
src/coreclr/vm/methodtable.h	Removes ArrayClass forward decl and NativeImageDumper friends.
src/coreclr/vm/methodtable.inl	Implements MethodTable::GetRank() using BaseSize - ARRAYBASE_BASESIZE.
src/coreclr/vm/object.inl	Computes lower-bounds offset using pMT->GetRank() directly.
src/coreclr/vm/vars.hpp	Removes ArrayClass forward decl.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/DataType.cs	Removes DataType.ArrayClass.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds Globals.ArrayBaseSize.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Computes multidim rank from BaseSize using Globals.ArrayBaseSize.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/EEClass.cs	Deletes managed ArrayClass data reader.
src/native/managed/cdac/tests/ContractDescriptor/TargetTests.SubDescriptors.cs	Removes ArrayClass size-only descriptor entry.
src/native/managed/cdac/tests/MethodTableTests.cs	Adds ValidateMultidimArrayRank coverage for rank derivation.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.cs	Removes ArrayClassFields descriptor.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.Object.cs	Updates mock array BaseSize to encode rank for multidim arrays; uses EEClass directly.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.RuntimeTypeSystem.cs	Removes AddArrayClass; adds Globals.ArrayBaseSize to the mock target.
src/native/managed/cdac/tests/ObjectTests.cs	Updates expected multidim array data pointer to account for rank-encoded bounds in BaseSize.

[max-charlamb]

@copilot, please update RuntimeTypeSystem.md docs with the relevant changes.

[Copilot]

@copilot, please update RuntimeTypeSystem.md docs with the relevant changes.

Done in 6e4b409. Updated RuntimeTypeSystem.md to: remove the ArrayClass | Rank data descriptor row, add ArrayBaseSize to the globals table, and update the IsArray pseudocode to derive multidim rank from BaseSize instead of reading from ArrayClass.

[max-charlamb]

@copilot , please fix the build break in linux-x64 checked CLR_Tools_Tests caused by the modified cDAC unit tests

[max-charlamb]

lgtm from a cDAC perspective once the cDAC unit tests pass CI

[Copilot]

@copilot , please fix the build break in linux-x64 checked CLR_Tools_Tests caused by the modified cDAC unit tests

Fixed in 0e7648e. The ValidateMultidimArrayRank method was missing [Theory] and [ClassData(typeof(MockTarget.StdArch))] attributes, triggering xUnit1013. All 916 cDAC tests pass locally.