`@errorCast` crashes on inferred error set

[andrewrk]

Zig Version

0.12.0-dev.705+af40bce08

Steps to Reproduce and Observed Behavior

const std = @import("std");

test {
    const bar: error{Bad}!i32 = @errorCast(foo());
    std.testing.expect((try bar) == 1234);
}

fn foo() !i32 {
    return 1234;
}

$ stage4/bin/zig test test3.zig 
thread 1049783 panic: reached unreachable code
Analyzing test3.zig: test3.zig:test_0
      %6 = dbg_block_begin()
      %7 = dbg_stmt(2, 5)
      %8 = block_comptime({
        %9 = error_set_decl(parent, {
          Bad,
        }) 
        %10 = error_union_type(%9, @InternPool.Index.i32_type) 
        %11 = break(%8, %10)
      }) 
      %12 = dbg_stmt(2, 33)
      %13 = decl_val("foo") 
      %14 = dbg_stmt(2, 47)
      %15 = call(.auto, %13, []) 
    > %16 = extended(error_cast(%8, %15)) 
      %17 = as_node(%8, %16) 
      %18 = dbg_var_val(%17, "bar")
      %19 = save_err_ret_index(%17)
      %20 = dbg_stmt(3, 5)
      %21 = decl_ref("std") 
      %22 = dbg_stmt(3, 8)
      %23 = field_ptr(%21, "testing") 
      %24 = dbg_stmt(3, 16)
      %25 = dbg_stmt(3, 23)
      %26 = field_call(nodiscard .auto, %23, "expect", [
        {
          %27 = dbg_stmt(3, 25)
          %28 = try(%17, {
            %29 = err_union_code(%17) 
            %30 = dbg_stmt(3, 25)
            %31 = ret_node(%29) 
          }) 
          %32 = int(1234)
          %33 = cmp_eq(%28, %32) 
          %34 = break_inline(%26, %33)
        },
      ]) 
      %35 = dbg_block_end()
      %36 = restore_err_ret_index(%5, %4294967211)
      %37 = break(%5, @InternPool.Index.void_value)
    For full context, use the command
      zig ast-check -t test3.zig

  in test3.zig: test3.zig:test_0
    > %5 = block({%6..%37}) 

/home/andy/Downloads/zig/src/type.zig:2874:26: 0x691d46a in errorSetNames (zig)
                .none => unreachable, // unresolved inferred error set
                         ^
/home/andy/Downloads/zig/src/Sema.zig:21782:69: 0x6c9baa6 in zirErrorCast (zig)
        if (!operand_ty.isAnyError(mod) and operand_ty.errorSetNames(mod).len == 0) break :disjoint true;
                                                                    ^
/home/andy/Downloads/zig/src/Sema.zig:1255:65: 0x68d024f in analyzeBodyInner (zig)
                    .error_cast         => try sema.zirErrorCast(         block, extended),
                                                                ^
/home/andy/Downloads/zig/src/Sema.zig:5887:34: 0x72841bb in resolveBlockBody (zig)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
/home/andy/Downloads/zig/src/Sema.zig:5870:33: 0x6ccc160 in zirBlock (zig)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
/home/andy/Downloads/zig/src/Sema.zig:1578:49: 0x68d7947 in analyzeBodyInner (zig)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
/home/andy/Downloads/zig/src/Sema.zig:917:30: 0x6b9ff78 in analyzeBody (zig)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
/home/andy/Downloads/zig/src/Module.zig:4847:21: 0x68a4826 in analyzeFnBody (zig)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
/home/andy/Downloads/zig/src/Module.zig:3442:40: 0x664a7fd in ensureFuncBodyAnalyzed (zig)
            var air = mod.analyzeFnBody(func_index, sema_arena) catch |err| switch (err) {
                                       ^
/home/andy/Downloads/zig/src/Compilation.zig:3458:42: 0x66488cd in processOneJob (zig)
            module.ensureFuncBodyAnalyzed(func) catch |err| switch (err) {
                                         ^
/home/andy/Downloads/zig/src/Compilation.zig:3395:30: 0x647bf5b in performAllTheWork (zig)
            try processOneJob(comp, work_item, main_progress_node);
                             ^
/home/andy/Downloads/zig/src/Compilation.zig:2194:31: 0x64774ec in update (zig)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/andy/Downloads/zig/src/main.zig:4194:24: 0x64a6530 in updateModule (zig)
        try comp.update(main_progress_node);
                       ^
/home/andy/Downloads/zig/src/main.zig:3597:17: 0x64c96c1 in buildOutputType (zig)
    updateModule(comp) catch |err| switch (err) {
                ^
/home/andy/Downloads/zig/src/main.zig:275:31: 0x631dba7 in mainArgs (zig)
        return buildOutputType(gpa, arena, args, .zig_test);
                              ^
/home/andy/Downloads/zig/src/main.zig:213:20: 0x631ac05 in main (zig)
    return mainArgs(gpa, arena, args);
                   ^
/home/andy/Downloads/zig/lib/std/start.zig:486:37: 0x631a61e in main (zig)
    std.os.argv = @as([*][*:0]u8, @ptrCast(c_argv))[0..@as(usize, @intCast(c_argc))];
                                    ^
???:?:?: 0x7f081db3dacd in ??? (libc.so.6)
Unwind information for `libc.so.6:0x7f081db3dacd` was not available, trace may be incomplete

Aborted (core dumped)

Expected Behavior

Test passed.