Make GetMethodInfo work for non-jit'ed code

[leculver]

Fix GetMethodByHandle for struct methods and generic method instantiations

Problem

GetMethodByHandle had two related bugs in DacMethodLocator.GetMethodInfo:

1. Struct methods returned null (Get ClrMethod from virtual method of struct #1306): The old code unconditionally called GetCodeHeaderData(NativeCodeAddr) in the same conditional as GetMethodDescData. When HasNativeCode == 0 (unboxing stubs, un-jitted inherited methods like ToString/Equals/GetHashCode), NativeCodeAddr is 0 and GetCodeHeaderData fails, causing GetMethodInfo to return false — which made GetMethodByHandle return null.

2. Value-type generic method instantiations reported wrong compilation info (Missing some compilation information for generic methods #935): For methods like Echo<int>(), the old code's slot-based lookup via GetMethodTableSlot returned the generic method definition (uninstantiated stub) instead of the JIT'd instantiation, yielding CompilationType=None and HotSize=0 even though WinDbg's !DumpMD correctly shows the method as jitted. The reporter's own investigation confirmed that GetCodeHeaderData(NativeCodeAddr) returns the correct data while the slot-based path does not.

Fix

Restructured GetMethodInfo into a three-tier approach:

1. Primary path (HasNativeCode != 0): Use GetCodeHeaderData(NativeCodeAddr) to get the correct JIT type and code size. This handles all jitted methods including value-type generic instantiations (the Missing some compilation information for generic methods #935 scenario).

2. Slot-based fallback (HasNativeCode == 0 but slot has code): Try GetMethodTableSlot + GetCodeHeaderData(slot). This is a defensive path for cases where a per-instantiation MethodDesc has HasNativeCode=0 but the method table slot points to shared JIT'd code (e.g., reference-type generic instantiations sharing code via __Canon).

3. No native code: Return CompilationType.None with default HotColdRegions for methods that genuinely haven't been JIT compiled.

Tests

Six new regression tests covering both issues:

Test	Scenario
GetMethodByHandle_StructImplementingInterface_FindsAllMethods	All methods on StructWithInterface resolve via GetMethodByHandle (#1306)
StructMethodCompilationType_MatchesJitStatus	Struct has both jitted and un-jitted methods with correct CompilationType (#1306)
GetMethodByHandle_ValueTypeGenericMethod_ReturnsJittedInfo	Echo<int>() reports CompilationType=Jit and non-zero HotSize (#935 exact scenario)
GetMethodByHandle_GenericMethodWithRefType_ReturnsJittedInfo	GenericClass<bool,int,float,string,object>.Invoke resolves correctly (#935)
GetMethodByHandle_RefTypeGenericInstantiation_ResolvesAllMethods	All methods on a ref-type generic instantiation from the heap resolve (#935)

All tests pass on both Windows (.NET Framework dumps) and Linux (.NET Core 10 dumps).

Fixes #1306. Fixes #935. (CompilationType and HotSize; the Name truncation sub-issue is tracked separately.)

[Copilot]

Pull request overview

This PR fixes ClrRuntime.GetMethodByHandle resolution for method handles whose MethodDesc exists but which don’t have code header data available (commonly for non-JIT’ed methods and some stubs), by no longer requiring GetCodeHeaderData to succeed in order to return MethodInfo. It also adds a regression scenario and tests around struct interface dispatch to cover issue #1306.

Changes:

• Update DacMethodLocator.GetMethodInfo to succeed when GetMethodDescData succeeds even if code header/native code data is unavailable, returning CompilationType.None + default HotColdRegions in that case.
• Extend the Types test target and shared test library to exercise struct interface dispatch (unboxing stub scenario).
• Add regression tests validating GetMethodByHandle can resolve methods for a struct implementing an interface, and asserting compilation-type behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
src/Microsoft.Diagnostics.Runtime/DacImplementation/DacMethodLocator.cs	Decouples MethodDesc lookup from code header lookup; returns a usable MethodInfo even when native code metadata can’t be read.
src/Microsoft.Diagnostics.Runtime.Tests/src/MethodTests.cs	Adds regression tests for struct/interface method handle resolution and compilation-type expectations.
src/TestTargets/Types/Types.cs	Triggers struct interface dispatch in the dump target to reproduce issue conditions.
src/TestTargets/Shared/SharedLibrary.cs	Adds IStructTest and StructWithInterface used by the new dump/test scenario.