Fixed size arrays of structs produce incorrect padding [C#, master]

[develmi]

padding_bug_prepro.zip

I did my best to narrow this problem down. It looks like flatc.exe produces wrong padding for fixed arrays of structs in c#.
Fixed size array of longs is generated correctly:

    builder.Prep(8, 80);
    builder.PutLong(Int2);
    for (int _idx0 = 8; _idx0 > 0; _idx0--) {
      builder.PutLong(IntStruct[_idx0-1]);
    }
    builder.Pad(4); // <- correctly placed padding
    builder.PutInt(Int1);

But in the case of array of structs:

    builder.Prep(8, 80);
    builder.PutLong(Int2);
    builder.Pad(4); // <- incorrectly placed padding, unnecessary padding of 4 bytes
    for (int _idx0 = 8; _idx0 > 0; _idx0--) {
      builder.Prep(8, 8); // same thing, results in one more alignment, producing extra 4 bytes
      builder.PutLong(int_struct_LongField[_idx0-1]);
    }
    builder.PutInt(Int1);

Both schemes should result in exactly the same buffer layout: there is no difference in laying out array of longs and array of structs that contain a single long.
As you can see in the attachment, incorrect padding leads to everything to be offset by a few bytes

Thank you!

[aardappel]

@svenk177 who wrote this in #5313

[svenk177]

Thanks for sharing!

There seems to be a missing check for arrays of structs in InlineAlignment.
Changing it to:

inline size_t InlineAlignment(const Type &type) {
  if (IsStruct(type)) {
    return type.struct_def->minalign;
  } else if (IsArray(type)) {
    return IsStruct(type.VectorType()) ? type.struct_def->minalign : SizeOf(type.element);
  } else {
    return SizeOf(type.base_type);
  }
}

should fix it. Can you confirm?

[develmi]

Hey, thanks! Your changes solve the problem.

[github-actions]

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