[release/10.0] Fix ComInterfaceGenerator collision on same-named methods in disjoint cross-assembly bases

[Copilot]

main PR AaronRobinsonMSFT@55aa5e6

Addresses #122708 in .NET 10.

Description

Cross-assembly [GeneratedComInterface] inheritance could fail generation when disjoint external bases each exposed a same-named method (customer repro: MyMethod), producing CS8785 from a ComMethodInfo dictionary key collision. This PR ports the servicing-safe dedup fix for release/10.0 and adds targeted regression coverage.

Customer Impact

Without this fix, valid cross-assembly COM interface hierarchies fail to compile under source generation, blocking .NET 10 migration scenarios reported by enterprise customers.

Regression

No. This is a latent key-collision bug in external-interface handling, surfaced by specific same-name cross-assembly method shapes.

Testing

• Reproduced pre-fix failure (CS8785 with duplicate ComMethodInfo key).
• Added regression assets/tests for the customer shape (combined + standalone variants).
• Ran ComInterfaceGenerator.Tests (with standard failing/ignore/outerloop exclusions); new tests and suite pass.

Risk

Low. Change is surgical and confined to generator-internal key identity for externally-defined methods; no public API, generated source contract, or runtime behavior changes.

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[Copilot]

Pull request overview

Ports a servicing-safe fix to the ComInterfaceGenerator for release/10.0 to prevent key collisions when collecting externally-defined COM interface methods that share the same name across disjoint base interfaces (cross-assembly inheritance scenario, issue #122708).

Changes:

• Extend generator-internal ComMethodInfo identity for externally-defined methods with a stable per-symbol ExternalSymbolId (doc comment id / fully-qualified fallback) to avoid dictionary key collisions.
• Add SharedTypes test assets that model two external base interfaces with same-named methods.
• Add cross-assembly inheritance regression coverage validating combined and standalone implementations.

Show a summary per file

File	Description
src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/BaseInterfaces/ISameNameMethodsDifferentAssembly.cs	Adds external base interfaces with same-named MyMethod to reproduce the collision shape across assemblies.
src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Tests/Interfaces/IDerivedFromExternalSameName.cs	Adds derived test interfaces that inherit the new external bases (with SYSLIB1230 suppressed, consistent with existing tests).
src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Tests/CrossAssemblyInheritanceTests.cs	Adds regression tests covering both-disjoint-bases and standalone base-path behavior through StrategyBasedComWrappers.
src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/ComMethodInfo.cs	Fixes external-method keying by incorporating ExternalSymbolId into record equality/hash for externally-defined methods.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0