Returning an error from an error union with a 0 length array fails with -ofmt=c

[MasonRemaley]

Zig Version

0.14.0-dev.737+30b4a87db

Steps to Reproduce and Observed Behavior

Minimal repro thanks to @ianprime0509:

test {
    try @import("std").testing.expectError(error.E, f());
}

fn f() error{E}![0]u8 {
    return error.E;
}

Stack trace

build/stage4/bin/zig test lib/std/std.zig -target x86_64-linux -ofmt=c -lc --test-filter "error-union-zero-len-array"
thread 57888 panic: reached unreachable code
/home/mason/Documents/zig/lib/std/debug.zig:404:14: 0x5b4e62c in assert (zig)
    if (!ok) unreachable; // assertion failure
             ^S
/home/mason/Documents/zig/src/codegen/c.zig:8089:15: 0x753666d in freeLocal (zig)
        assert(!f.allocs.contains(local_index));
              ^l.Crc(u32,.{ .polynomial = 7
/home/mason/Documents/zig/src/codegen/c.zig:8066:18: 0x753690d in die (zig)
    try freeLocal(f, inst, local_index, ref_inst);
                 ^n_15613
/home/mason/Documents/zig/src/codegen/c.zig:8105:16: 0x787589d in feed (zig)
        try die(bt.f, bt.inst, op_ref);
               ^ion
/home/mason/Documents/zig/src/codegen/c.zig:7122:24: 0x78ba91a in airAggregateInit (zig)
            try bt.feed(element);
                       ^r
/home/mason/Documents/zig/src/codegen/c.zig:3257:54: 0x753caf0 in genBodyInner (zig)
            .aggregate_init   => try airAggregateInit(f, inst),
                                                     ^
/home/mason/Documents/zig/src/codegen/c.zig:3032:25: 0x753f616 in genBody (zig)
        try genBodyInner(f, body);
                        ^
/home/mason/Documents/zig/src/codegen/c.zig:3073:20: 0x7129613 in genBodyResolveState (zig)
        try genBody(f, body);
                   ^
/home/mason/Documents/zig/src/codegen/c.zig:4941:28: 0x789ba92 in airCondBr (zig)
    try genBodyResolveState(f, inst, liveness_condbr.then_deaths, then_body, false);
                           ^
/home/mason/Documents/zig/src/codegen/c.zig:3232:47: 0x753b78d in genBodyInner (zig)
            .cond_br          => try airCondBr(f, inst),
                                              ^
/home/mason/Documents/zig/src/codegen/c.zig:3071:25: 0x71295dd in genBodyResolveState (zig)
        try genBodyInner(f, body);
                        ^s
/home/mason/Documents/zig/src/codegen/c.zig:4605:28: 0x787f0ee in lowerBlock (zig)
    try genBodyResolveState(f, inst, &.{}, body, true);
                           ^es
/home/mason/Documents/zig/src/codegen/c.zig:4582:22: 0x787f852 in airBlock (zig)
    return lowerBlock(f, inst, @ptrCast(f.air.extra[extra.end..][0..extra.data.body_len]));
                     ^atures
/home/mason/Documents/zig/src/codegen/c.zig:3220:46: 0x753afa4 in genBodyInner (zig)
            .block            => try airBlock(f, inst),
                                             ^
/home/mason/Documents/zig/src/codegen/c.zig:3032:25: 0x753f616 in genBody (zig)
        try genBodyInner(f, body);
                        ^res
/home/mason/Documents/zig/src/codegen/c.zig:3073:20: 0x7129613 in genBodyResolveState (zig)
        try genBody(f, body);ls
                   ^
/home/mason/Documents/zig/src/codegen/c.zig:2833:28: 0x712824e in genFunc (zig)
    try genBodyResolveState(f, undefined, &.{}, main_body, false);
                           ^
/home/mason/Documents/zig/src/link/C.zig:252:20: 0x712a6b7 in updateFunc (zig)
    codegen.genFunc(&function) catch |err| switch (err) {
                   ^.gfx1200
/home/mason/Documents/zig/src/link.zig:426:82: 0x6c75111 in updateFunc (zig)
                return @as(*tag.Type(), @fieldParentPtr("base", base)).updateFunc(pt, func_index, air, liveness);
                                                                                 ^
/home/mason/Documents/zig/src/Zcu/PerThread.zig:826:22: 0x67e3889 in linkerUpdateFunc (zig)
        lf.updateFunc(pt, func_index, air, liveness) catch |err| switch (err) {
                     ^apple_a14
/home/mason/Documents/zig/src/Compilation.zig:4070:36: 0x635dd00 in processOneCodegenJob (zig)
            try pt.linkerUpdateFunc(func.func, func.air);
                                   ^
/home/mason/Documents/zig/src/Compilation.zig:4042:33: 0x635ce3f in codegenThread (zig)
            processOneCodegenJob(tid, comp, codegen_job) catch |job_error| {
                                ^
/home/mason/Documents/zig/lib/std/Thread/Pool.zig:178:50: 0x635cf81 in runFn (zig)
            @call(.auto, func, .{id.?} ++ closure.arguments);
                                                 ^
/home/mason/Documents/zig/lib/std/Thread/Pool.zig:291:32: 0x630b36d in worker (zig)
            run_node.data.runFn(&run_node.data, id);
                               ^58
/home/mason/Documents/zig/lib/std/Thread.zig:409:13: 0x6025b6a in callFn__anon_74738 (zig)
            @call(.auto, f, args);
            ^rc.cpu.ultrasparc
/home/mason/Documents/zig/lib/std/Thread.zig:678:30: 0x5da3612 in entryFn (zig)
                return callFn(f, args_ptr.*);
                             ^
./nptl/pthread_create.c:442:8: 0x7d0974894ac2 in start_thread (pthread_create.c)
../sysdeps/unix/sysv/linux/x86_64/clone3.S:81:0: 0x7d097492684f in ??? (../sysdeps/unix/sysv/linux/x86_64/clone3.S)
???:?:?: 0x0 in ??? (???)
fish: Job 1, 'build/stage4/bin/zig test lib/s…' terminated by signal SIGABRT (Abort)

Expected Behavior

I expected the test to pass.

[ianprime0509]

I was able to reduce this further:

test {
    g(error.E, .{});
}

pub fn g(a: anyerror, b: anyerror![0]u8) void {
    if (b) |v| {
        h(.{ a, v });
    } else |err| {
        h(.{ a, err });
    }
}

pub fn h(_: anytype) void {}

Here's the output of zig test -ofmt=c test.zig as of 0.14.0-dev.841+ea847535f:

Stack trace

thread 1527409 panic: reached unreachable code
/var/home/ian/src/zig/lib/std/debug.zig:384:14: 0x17dc92c in assert (zig)
    if (!ok) unreachable; // assertion failure
             ^
/var/home/ian/src/zig/src/codegen/c.zig:8089:15: 0x31c488d in freeLocal (zig)
        assert(!f.allocs.contains(local_index));
              ^
/var/home/ian/src/zig/src/codegen/c.zig:8066:18: 0x31c4b2d in die (zig)
    try freeLocal(f, inst, local_index, ref_inst);
                 ^
/var/home/ian/src/zig/src/codegen/c.zig:8105:16: 0x3503c5d in feed (zig)
        try die(bt.f, bt.inst, op_ref);
               ^
/var/home/ian/src/zig/src/codegen/c.zig:7122:24: 0x3548cda in airAggregateInit (zig)
            try bt.feed(element);
                       ^
/var/home/ian/src/zig/src/codegen/c.zig:3257:54: 0x31cad10 in genBodyInner (zig)
            .aggregate_init   => try airAggregateInit(f, inst),
                                                     ^
/var/home/ian/src/zig/src/codegen/c.zig:3032:25: 0x31cd836 in genBody (zig)
        try genBodyInner(f, body);
                        ^
/var/home/ian/src/zig/src/codegen/c.zig:3073:20: 0x2db31f3 in genBodyResolveState (zig)
        try genBody(f, body);
                   ^
/var/home/ian/src/zig/src/codegen/c.zig:4941:28: 0x3529e52 in airCondBr (zig)
    try genBodyResolveState(f, inst, liveness_condbr.then_deaths, then_body, false);
                           ^
/var/home/ian/src/zig/src/codegen/c.zig:3232:47: 0x31c99ad in genBodyInner (zig)
            .cond_br          => try airCondBr(f, inst),
                                              ^
/var/home/ian/src/zig/src/codegen/c.zig:3071:25: 0x2db31bd in genBodyResolveState (zig)
        try genBodyInner(f, body);
                        ^
/var/home/ian/src/zig/src/codegen/c.zig:4605:28: 0x350d4ae in lowerBlock (zig)
    try genBodyResolveState(f, inst, &.{}, body, true);
                           ^
/var/home/ian/src/zig/src/codegen/c.zig:4582:22: 0x350dc12 in airBlock (zig)
    return lowerBlock(f, inst, @ptrCast(f.air.extra[extra.end..][0..extra.data.body_len]));
                     ^
/var/home/ian/src/zig/src/codegen/c.zig:3220:46: 0x31c91c4 in genBodyInner (zig)
            .block            => try airBlock(f, inst),
                                             ^
/var/home/ian/src/zig/src/codegen/c.zig:3032:25: 0x31cd836 in genBody (zig)
        try genBodyInner(f, body);
                        ^
/var/home/ian/src/zig/src/codegen/c.zig:3073:20: 0x2db31f3 in genBodyResolveState (zig)
        try genBody(f, body);
                   ^
/var/home/ian/src/zig/src/codegen/c.zig:2833:28: 0x2db1e2e in genFunc (zig)
    try genBodyResolveState(f, undefined, &.{}, main_body, false);
                           ^
/var/home/ian/src/zig/src/link/C.zig:252:20: 0x2db4297 in updateFunc (zig)
    codegen.genFunc(&function) catch |err| switch (err) {
                   ^
/var/home/ian/src/zig/src/link.zig:426:82: 0x28fdaa1 in updateFunc (zig)
                return @as(*tag.Type(), @fieldParentPtr("base", base)).updateFunc(pt, func_index, air, liveness);
                                                                                 ^
/var/home/ian/src/zig/src/Zcu/PerThread.zig:826:22: 0x246b7f9 in linkerUpdateFunc (zig)
        lf.updateFunc(pt, func_index, air, liveness) catch |err| switch (err) {
                     ^
/var/home/ian/src/zig/src/Compilation.zig:4070:36: 0x1fe64d0 in processOneCodegenJob (zig)
            try pt.linkerUpdateFunc(func.func, func.air);
                                   ^
/var/home/ian/src/zig/src/Compilation.zig:4042:33: 0x1fe560f in codegenThread (zig)
            processOneCodegenJob(tid, comp, codegen_job) catch |job_error| {
                                ^
/var/home/ian/src/zig/lib/std/Thread/Pool.zig:178:50: 0x1fe5751 in runFn (zig)
            @call(.auto, func, .{id.?} ++ closure.arguments);
                                                 ^
/var/home/ian/src/zig/lib/std/Thread/Pool.zig:291:32: 0x1f93b1d in worker (zig)
            run_node.data.runFn(&run_node.data, id);
                               ^
/var/home/ian/src/zig/lib/std/Thread.zig:409:13: 0x1cb255a in callFn__anon_74768 (zig)
            @call(.auto, f, args);
            ^
/var/home/ian/src/zig/lib/std/Thread.zig:678:30: 0x1a31902 in entryFn (zig)
                return callFn(f, args_ptr.*);
                             ^
???:?:?: 0x7fd4f50fe1b6 in ??? (libc.so.6)
Unwind information for `libc.so.6:0x7fd4f50fe1b6` was not available, trace may be incomplete

???:?:?: 0x7fd4f51803cb in ??? (libc.so.6)
Aborted (core dumped)