No error when using [D2DInputSimple(n)] but reading outside of current pixel

[rickbrew]

I only noticed this recently when someone on the PDN forum posted a shader that was using D2DInputSimple even though they were doing complex sampling: https://forums.getpaint.net/topic/124551-gpu-median-filter/

To repro this, take any D2D shader that specifies [D2DInputComplex(n)] and replace it with [D2DInputSimple(n)].

Two weird things happen:

1. No compile-time error, which I was expecting d2d1effecthelpers.hlsli to force, e.g. by mapping D2DSampleInputAtOffset(n) to some invalid syntax or the equivalent of a #pragma error
2. The shader works fine?! What's the actual difference here then? I wonder if it would confuse/break D2D if it tries to use the shader as a linked shader

My proposal is that ComputeSharp.D2D1 should detect this and emit an error.