compiler segfault with empty union

[billzez]

Zig Version

0.11.0-dev.5

Steps to Reproduce and Observed Behavior

const U = union(enum) {};

fn f2(u: U) void {
    _ = u;
}

pub fn main() void {
    _ = f2;
}

Expected Behavior

stage1 gives an error:

./main.zig:1:11: error: unions must have 1 or more fields
const U = union(enum) {};

[nektro]

stack trace on 0.11.0-dev.6+2943df016

thread 662502 panic: index out of bounds
/home/meghan/src/zig/src/codegen/llvm.zig:7900:34: 0xc913a7 in codegen.llvm.FuncGen.airArg (zig2)
        const arg_val = self.args[self.arg_index];
                                 ^
/home/meghan/src/zig/src/codegen/llvm.zig:4531:51: 0xc7844d in codegen.llvm.FuncGen.genBody (zig2)
                .arg            => try self.airArg(inst),
                                                  ^
/home/meghan/src/zig/src/codegen/llvm.zig:1225:19: 0xc73227 in codegen.llvm.Object.updateFunc (zig2)
        fg.genBody(air.getMainBody()) catch |err| switch (err) {
                  ^
/home/meghan/src/zig/src/link/Elf.zig:2411:74: 0x9bf0a7 in link.Elf.updateFunc (zig2)
        if (self.llvm_object) |llvm_object| return llvm_object.updateFunc(module, func, air, liveness);
                                                                         ^
/home/meghan/src/zig/src/link.zig:558:77: 0x7d3ca9 in link.File.updateFunc (zig2)
            .elf   => return @fieldParentPtr(Elf,   "base", base).updateFunc(module, func, air, liveness),
                                                                            ^
/home/meghan/src/zig/src/Module.zig:4385:37: 0x7b1221 in Module.ensureFuncBodyAnalyzed (zig2)
            comp.bin_file.updateFunc(mod, func, air, liveness) catch |err| switch (err) {
                                    ^
/home/meghan/src/zig/src/Compilation.zig:3065:42: 0x65fde3 in Compilation.processOneJob (zig2)
            module.ensureFuncBodyAnalyzed(func) catch |err| switch (err) {
                                         ^
/home/meghan/src/zig/src/Compilation.zig:3003:30: 0x64d66f in Compilation.performAllTheWork (zig2)
            try processOneJob(comp, work_item);
                             ^
/home/meghan/src/zig/src/Compilation.zig:2331:31: 0x645d1e in Compilation.update (zig2)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/meghan/src/zig/src/main.zig:3337:20: 0x5d12bf in main.updateModule (zig2)
    try comp.update();
                   ^
/home/meghan/src/zig/src/main.zig:3008:17: 0x518618 in main.buildOutputType (zig2)
    updateModule(gpa, comp, hook) catch |err| switch (err) {
                ^
/home/meghan/src/zig/src/main.zig:238:31: 0x4b10af in main.mainArgs (zig2)
        return buildOutputType(gpa, arena, args, .run);
                              ^
/home/meghan/src/zig/src/stage1.zig:56:24: 0x4b0725 in main (zig2)
        stage2.mainArgs(gpa, arena, args) catch unreachable;
                       ^

[Vexu]

Related #12376