Zig Version

Zig 0.15+

Steps to Reproduce and Observed Behavior

 extern var buffer: [*]addrspace(.storage_buffer) f32;

  export fn test_fn() void {
      _ = buffer[0]; // Error: illegal operation on logical pointer
  }

Build:
zig build-lib -target spirv64-vulkan -mcpu vulkan_v1_2+variable_pointers test.zig

Edit summary:
I was using [*]f32 addrspace(.storage_buffer) which is wrong => needs to be [*]addrspace(.storage_buffer) f32. The old error was leading me to believe the address space was being lost, but in reality it was not set correctly. Fixing this leads to the New Error. Fix 2 should solve this. Will post a pr soon.
Edit summary end.

Old Error:
test.zig:16:11: note: cannot perform arithmetic on pointers with address space 'generic' on target spirv-vulkan

New Error:
test.zig:16:11: note: cannot perform arithmetic on pointers with address space 'storage_buffer' on target spirv-vulkan

Fix 2

src/target.zig:569 unconditionally marks .storage_buffer as logical - which is true.
src/Sema.zig:23166 checks via arePointersLogical if indexing operations are allowed:

 if (target_util.arePointersLogical(target, as)) {
            return sema.failWithOwnedErrorMsg(block, msg: {
                const msg = try sema.errMsg(src, "illegal operation on logical pointer of type '{f}'", .{ty.fmt(pt)});

Which is wrong because .storage_buffer can support indexing via OpPtrAccessChain if variable_pointers_storage_buffer is enabled.
A quick fix would be to change src/target.zig:569 to:

.storage_buffer => !target.cpu.features.isEnabled(@intFromEnum(std.Target.spirv.Feature.variable_pointers)),

I would suggest a name change though, because arePointersLogical is not asking if indexing operations are allowed. .storage_buffer pointers are still logical. But they can also support Indexing.
Maybe something like:

 /// Returns whether new pointer values can be derived from existing pointers in the given
 /// address space. In SPIR-V, this corresponds to whether OpPtrAccessChain and similar
 /// pointer derivation operations are supported, which depends on capabilities like
 /// Addresses, VariablePointers, VariablePointersStorageBuffer, PhysicalStorageBufferAddresses
 pub fn canDerivePointers(target: *const std.Target, as: AddressSpace) bool {