Remove unused to_ir.Var.GlobalVar constructor

[mvanhorn]

Summary

Removes the to_ir.Var.GlobalVar constructor from the to_ir.Var union and the two elseif var_info._tag == "to_ir.Var.GlobalVar" arms in to_ir.lua that referenced it. Per issue #662 these are residual after the rest of the global-handling rewrite.

Why this matters

Issue #662 says to_ir.Var.GlobalVar is residual code. Confirmed by reading the function that produces to_ir.Var values:

ToIR:resolve_variable (src/pallene/to_ir.lua:237) only ever constructs to_ir.Var.LocalVar (line 255) inside its initial loop, then optionally promotes that value to to_ir.Var.Upvalue (line 288) when the declaration is captured by an enclosing function. There is no code path that constructs to_ir.Var.GlobalVar. The function asserts var is set, so it always returns either LocalVar or Upvalue.

That means the two elseif var_info._tag == "to_ir.Var.GlobalVar" arms in exp_to_value (line 1066) and exp_to_assignment (line 1314) are unreachable. The first arm contains only a -- Fallthrough to default comment; the second arm contains bb:append_cmd(ir.Cmd.GetGlobal(loc, dst, var_info.id)) which can never execute. The else branch with tagged_union.error(var_info._tag) still catches any future tag the compiler might add.

Changes

src/pallene/to_ir.lua: 5 lines removed across 3 spots.

• Line 31: GlobalVar = {"id"}, removed from the define_union("Var", { ... }) block.
• Lines 1066-1067 in exp_to_value: drop the elseif ... GlobalVar arm whose body is just a comment.
• Lines 1314-1315 in exp_to_assignment: drop the elseif ... GlobalVar arm whose bb:append_cmd(ir.Cmd.GetGlobal(...)) body is unreachable.

The two else branches that follow each removed elseif continue to call tagged_union.error(var_info._tag), so any new variant would still be caught loudly at runtime.

Testing

After the change, grep -rn 'GlobalVar' src/pallene/ returns no matches.

I do not have a Lua / busted toolchain in this environment, so I did not run the test suite locally. The change is mechanical removal of dead code; no logic flow is altered.

Closes #662

[hugomg]

Is this AI generated?

Please do not submit AI-generated code to pallene