SDK 10.0.400 regression: cross-assembly inline SRTP call throws in Release

[cmeeren]

An inline SRTP call from Aether 8.3.1 that works with SDK 10.0.303 compiles but throws at runtime with SDK 10.0.400, including optimized Release builds.

Repro steps

1. Extract the attached project: fsharp-aether-srtp-repro.zip
2. Run dotnet run -c Release.
3. Change global.json to SDK 10.0.303 and repeat for comparison.

Expected behavior

The program should output:

{ Value = 1 }

Actual behavior

With SDK 10.0.400:

Unhandled exception. System.NotSupportedException:
Dynamic invocation of op_HatEquals is not supported
   at Aether.Optic.set[a,b,c](a optic, b value)

SDK 10.0.303 produces the expected output.

Known workarounds

• Pin the SDK to 10.0.303.
• Rebuilding the unmodified Aether 8.3.1 source with SDK 10.0.303 also makes the SDK 10.0.400 consumer pass.
• --always-inline+ does not fix the failing Release call.

Related information

• Windows 11 Pro 10.0.26200, win-x64
• .NET SDK 10.0.400, commit 14fbf8d527
• .NET 10
• Aether 8.3.1
• Regression range: SDK 10.0.303 → 10.0.400
• Possibly related to Debugger: prefer no inlining in non-optimized builds #19548

[T-Gro]

This is a consequence of #19548, let's fix it with #20260 .

Affected producer libraries: compiled with F# 5.0 or earlier—before PR #6811 (f45ef819b5, July 2021) removed PseudoVal. Only binaries exposing required-inline definitions encoded with zero flag bits are affected, typically cross-assembly SRTP/inline APIs such as Aether.

Affected consumers: code compiled by a compiler containing PR #19548, notably SDK 10.0.400. The target framework or referenced FSharp.Core version alone does not determine exposure; the compiler that built the library does.

Rebuilding the library with F# 6+ avoids the bug.

[auduchinok]

@T-Gro Is it expected that #19548 got backported to .NET 10? I thought it'd only go to .NET 11 previews?