Assertion `incoming_count != 0' failed.

[bnoordhuis]

With commit 517e8ea:

fn S(comptime _: type) -> type {
    return union(enum) { M };
}

pub fn main() {
    switch (@typeOf(S(i8).M)) {}
}

Produces:

$ zig version
0.1.1.517e8ea4

$ zig build-exe x.zig
zig: /home/bnoordhuis/src/zig/src/ir.cpp:955: IrInstruction* ir_build_phi(IrBuilder*, Scope*, AstNode*, size_t, IrBasicBlock**, IrInstruction**): Assertion `incoming_count != 0' failed.

Backtrace:

#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007ffff3913f5d in __GI_abort () at abort.c:90
#2  0x00007ffff3909f17 in __assert_fail_base (fmt=<optimized out>, assertion=assertion@entry=0x555556e2a355 "incoming_count != 0", file=file@entry=0x555556e2a268 "/home/bnoordhuis/src/zig/src/ir.cpp", line=line@entry=955, function=function@entry=0x555556e2f5c0 <ir_build_phi(IrBuilder*, Scope*, AstNode*, unsigned long, IrBasicBlock**, IrInstruction**)::__PRETTY_FUNCTION__> "IrInstruction* ir_build_phi(IrBuilder*, Scope*, AstNode*, size_t, IrBasicBlock**, IrInstruction**)") at assert.c:92
#3  0x00007ffff3909fc2 in __GI___assert_fail (assertion=0x555556e2a355 "incoming_count != 0", file=0x555556e2a268 "/home/bnoordhuis/src/zig/src/ir.cpp", line=955, function=0x555556e2f5c0 <ir_build_phi(IrBuilder*, Scope*, AstNode*, unsigned long, IrBasicBlock**, IrInstruction**)::__PRETTY_FUNCTION__> "IrInstruction* ir_build_phi(IrBuilder*, Scope*, AstNode*, size_t, IrBasicBlock**, IrInstruction**)") at assert.c:101
#4  0x0000555555da36f1 in ir_build_phi (irb=0x7fffffffd4f0, scope=0x5555595dba30, source_node=0x555557667c70, incoming_count=0, incoming_blocks=0x0, incoming_values=0x0) at /home/bnoordhuis/src/zig/src/ir.cpp:955
#5  0x0000555555db2df9 in ir_gen_switch_expr (irb=0x7fffffffd4f0, scope=0x5555595dba30, node=0x555557667c70) at /home/bnoordhuis/src/zig/src/ir.cpp:4995
#6  0x0000555555db4a4b in ir_gen_node_raw (irb=0x7fffffffd4f0, node=0x555557667c70, scope=0x5555595dba30, lval=...) at /home/bnoordhuis/src/zig/src/ir.cpp:5441
#7  0x0000555555db4c7d in ir_gen_node_extra (irb=0x7fffffffd4f0, node=0x555557667c70, scope=0x5555595dba30, lval=...) at /home/bnoordhuis/src/zig/src/ir.cpp:5467
#8  0x0000555555db4d0d in ir_gen_node (irb=0x7fffffffd4f0, node=0x555557667c70, scope=0x5555595dba30) at /home/bnoordhuis/src/zig/src/ir.cpp:5473
#9  0x0000555555da81f2 in ir_gen_block (irb=0x7fffffffd4f0, parent_scope=0x5555595d8920, block_node=0x555557667bd0) at /home/bnoordhuis/src/zig/src/ir.cpp:2584
#10 0x0000555555db4537 in ir_gen_node_raw (irb=0x7fffffffd4f0, node=0x555557667bd0, scope=0x5555595d8920, lval=...) at /home/bnoordhuis/src/zig/src/ir.cpp:5385
#11 0x0000555555db4c7d in ir_gen_node_extra (irb=0x7fffffffd4f0, node=0x555557667bd0, scope=0x5555595d8920, lval=...) at /home/bnoordhuis/src/zig/src/ir.cpp:5467
#12 0x0000555555db4e93 in ir_gen (codegen=0x55555762edc0, node=0x555557667bd0, scope=0x5555595d8920, ir_executable=0x5555595d8730) at /home/bnoordhuis/src/zig/src/ir.cpp:5504
#13 0x0000555555db4fbc in ir_gen_fn (codegen=0x55555762edc0, fn_entry=0x5555595d86c0) at /home/bnoordhuis/src/zig/src/ir.cpp:5524
#14 0x0000555555d7042b in analyze_fn_body (g=0x55555762edc0, fn_table_entry=0x5555595d86c0) at /home/bnoordhuis/src/zig/src/analyze.cpp:3683
#15 0x0000555555d7111d in semantic_analyze (g=0x55555762edc0) at /home/bnoordhuis/src/zig/src/analyze.cpp:3900
#16 0x0000555555d9d43d in gen_root_source (g=0x55555762edc0) at /home/bnoordhuis/src/zig/src/codegen.cpp:5744
#17 0x0000555555d9e66c in codegen_build (g=0x55555762edc0) at /home/bnoordhuis/src/zig/src/codegen.cpp:6064
#18 0x0000555555dec8d1 in main (argc=3, argv=0x7fffffffdb18) at /home/bnoordhuis/src/zig/src/main.cpp:852

[andrewrk]

Thanks for the report. I think this has to do with the union having only 1 field.

Zig has runtime safety for unions, and there is an optimization where the secret enum field does not need to exist if there is only 1 field. Looks like a bug with that situation.

I'll look into this over the next couple days.