[dynamic dispatch] Explicit generic specialization with interface type crashes with error 99999

[NV-xiaoyongs]

Issue Description

Explicitly specializing a constrained generic function with an interface type — genericFunc<IFoo>(obj, 3.0) — crashes the compiler with error 99999: Unexpected context type for parameter info retrieval.

This is a different crash from #10263 (which uses implicit inference). When the same function is called with implicit inference (genericFunc(obj, 3.0)), the compiler correctly emits error 33180. The explicit specialization path hits a separate unhandled code path.

Reproducer Code

interface IFoo
{
    float calc(float x);
}

struct A : IFoo { float calc(float x) { return x * 2.0; } }
struct B : IFoo { float calc(float x) { return x + 10.0; } }

float genericFunc<T : IFoo>(T obj, float x)
{
    return obj.calc(x);
}

IFoo makeObj(int id)
{
    if (id == 0) return A();
    else return B();
}

RWStructuredBuffer<float> outputBuffer;

[numthreads(1, 1, 1)]
void computeMain(int id : SV_DispatchThreadID)
{
    IFoo obj = makeObj(id);
    float result = genericFunc<IFoo>(obj, 3.0);   // CRASH
    outputBuffer[0] = result;
}

Command line:

slangc repro.slang -target hlsl -stage compute -entry computeMain

Expected Behavior

The compiler emits error 33180 (consistent with the implicit inference case), since genericFunc(obj, 3.0) already produces that diagnostic.

Actual Behavior

(0): error 99999: Slang compilation aborted due to an exception of N5Slang13InternalErrorE: unexpected: Unexpected context type for parameter info retrieval

The crash occurs on all targets (spirv, hlsl, glsl).

Note: Changing to implicit inference — genericFunc(obj, 3.0) instead of genericFunc<IFoo>(obj, 3.0) — correctly produces:

error 33180: specializing '...' with an existential type is not allowed. All generic arguments must be statically resolvable at compile time.

Environment

• Slang Version: commit 6ffecd3 (master, 2026-02-26)
• OS: Linux 6.14.0-37-generic x86_64 (Ubuntu 24.04)

Additional Context

Found during issue #10290 testing. Related test file: tests/language-feature/dynamic-dispatch/diagnose-explicit-specialize-with-interface.slang.

This could be filed as a standalone issue or added as a note on #10263 since both involve interface types flowing into generic parameters.