Avoid using simple constants like 0 or 1 all over the place in unit tests

[nodakai]

We should replace simple constants given to system/library calls with something more distinguishable for the ease of debugging with system/library call tracer such as strace.

Let me emphasize that replacing them doesn't have to be perfect from the beginning. Perfectionism will not help anyone.

Example: a constant 0 here

assert_eq!(a.send_to(&[0], addr1), Ok(()));

eventually appears in the strace output log as

10793 sendto(12, "\0", 1, 0, {sa_family=AF_INET, sin_port=htons(9641), sin_addr=inet_addr("127.0.0.1")}, 16 <unfinished ...>

but the problem is, there are other unit tests which does send_to(2) of "\0". It's troublesome to find the source code line corresponding to the above log. If the original Rust code was written as

assert_eq!(a.send_to(b"x", addr1), Ok(()));

and the other send_to(2) calls used "y", "z" etc, we can easily find the above location from the output line which would look like

10793 sendto(12, "x", 1, 0, {sa_family=AF_INET, sin_port=htons(9641), sin_addr=inet_addr("127.0.0.1")}, 16 <unfinished ...>

My motivation is: I'm investigating why the unit test driver of libstd sometimes get stuck like this:

25174 pts/20   Ss     0:06  \_ /bin/zsh
 9886 pts/20   S+     0:00  |   \_ strace -f -o /tmp/test-03-13-14.log ./x86_64-unknown-linux-gnu/stage2/test/stdtest-x86_64-unknown-linux-gnu
 9891 pts/20   Sl+    0:02  |       \_ ./x86_64-unknown-linux-gnu/stage2/test/stdtest-x86_64-unknown-linux-gnu
10895 pts/20   Z+     0:00  |           \_ [sleep] <defunct>
10921 pts/20   Z+     0:00  |           \_ [stdtest-x86_64-] <defunct>
10971 pts/20   Z+     0:00  |           \_ [stdtest-x86_64-] <defunct>
11001 pts/20   Z+     0:00  |           \_ [stdtest-x86_64-] <defunct>

I can probably post a (partial) fix of #[test] fn recv_from_timeout() in libstd/io/net/udp.rs later.

$ ag '1079[23]|10800' test-03-13-14.log
28336:9891  <... clone resumed> child_stack=0x7f71ebdfdfb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7f71ebdfe9d0, tls=0x7f71ebdfe700, child_tidptr=0x7f71ebdfe9d0) = 10792
28350:10792 set_robust_list(0x7f71ebdfe9e0, 24 <unfinished ...>
28358:10792 <... set_robust_list resumed> )   = 0
28359:10792 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f722c6cc000
28360:10792 sigaltstack({ss_sp=0x7f722c6cc000, ss_flags=0, ss_size=8192}, NULL) = 0
28361:10792 sched_getaffinity(10792, 32, {ff, 0, 0, 0}) = 32
28362:10792 clone(child_stack=0x7f71eafeafb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7f71eafeb9d0, tls=0x7f71eafeb700, child_tidptr=0x7f71eafeb9d0) = 10793
28363:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
28366:10793 set_robust_list(0x7f71eafeb9e0, 24 <unfinished ...>
28538:10793 <... set_robust_list resumed> )   = 0
28543:10793 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...>
28676:10793 <... mmap resumed> )              = 0x7f722c6be000
28679:10793 sigaltstack({ss_sp=0x7f722c6be000, ss_flags=0, ss_size=8192} <unfinished ...>
28683:10793 <... sigaltstack resumed> , NULL) = 0
28686:10793 sched_getaffinity(10793, 32,  <unfinished ...>
28690:10793 <... sched_getaffinity resumed> {ff, 0, 0, 0}) = 32
28696:10793 getcwd( <unfinished ...>
28699:10793 <... getcwd resumed> "/home/nodakai/src/rust-HEAD", 2048) = 28
28703:10793 getcwd( <unfinished ...>
28706:10793 <... getcwd resumed> "/home/nodakai/src/rust-HEAD", 2048) = 28
28710:10793 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP <unfinished ...>
28714:10793 <... socket resumed> )            = 12
28717:10793 bind(12, {sa_family=AF_INET, sin_port=htons(9640), sin_addr=inet_addr("127.0.0.1")}, 16 <unfinished ...>
28720:10793 <... bind resumed> )              = 0
28724:10793 clone( <unfinished ...>
28729:10793 <... clone resumed> child_stack=0x7f71ebbfcfb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7f71ebbfd9d0, tls=0x7f71ebbfd700, child_tidptr=0x7f71ebbfd9d0) = 10800
28731:10793 select(13, [12], NULL, NULL, {0, 20000} <unfinished ...>
29248:10800 set_robust_list(0x7f71ebbfd9e0, 24 <unfinished ...>
29463:10800 <... set_robust_list resumed> )   = 0
30101:10800 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...>
30744:10800 <... mmap resumed> )              = 0x7f722c6d2000
31039:10793 <... select resumed> )            = 0 (Timeout)
31041:10793 select(13, [12], NULL, NULL, {0, 0} <unfinished ...>
31043:10793 <... select resumed> )            = 0 (Timeout)
31045:10793 sendto(12, "\0", 1, 0, {sa_family=AF_INET, sin_port=htons(9641), sin_addr=inet_addr("127.0.0.1")}, 16 <unfinished ...>
31047:10793 <... sendto resumed> )            = 1
31049:10793 recvfrom(12,  <unfinished ...>
31291:10800 sigaltstack({ss_sp=0x7f722c6d2000, ss_flags=0, ss_size=8192} <unfinished ...>
31747:10800 <... sigaltstack resumed> , NULL) = 0
32023:10800 sched_getaffinity(10800, 32,  <unfinished ...>
32039:10800 <... sched_getaffinity resumed> {ff, 0, 0, 0}) = 32
32056:10800 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP <unfinished ...>
32062:10800 <... socket resumed> )            = 8
32072:10800 bind(8, {sa_family=AF_INET, sin_port=htons(9641), sin_addr=inet_addr("127.0.0.1")}, 16 <unfinished ...>
32078:10800 <... bind resumed> )              = 0
32082:10800 recvfrom(8,  <unfinished ...>
52140:10792 <... futex resumed> )             = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
52143:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
63288:10792 <... futex resumed> )             = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
63290:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
75761:10792 <... futex resumed> )             = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
75765:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
75802:10792 <... futex resumed> )             = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
75804:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
88756:10793 <... recvfrom resumed> 0x7f71eafea27f, 1, 0, 0x7f71eafea0b8, 0x7f71eafea0ac) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
88758:10792 <... futex resumed> )             = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
88761:10792 futex(0x7f722ac2da8c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
89145:10793 recvfrom(12,  <unfinished ...>
172341:10800 +++ killed by SIGINT +++
172342:10793 +++ killed by SIGINT +++
172343:10792 +++ killed by SIGINT +++

[steveklabnik]

Triage: i am not aware of any efforts to update the test suite in this regard.

[brson]

While this is a good objective, I think without specifics of which test cases need to be cleaned up with better constants it's not actionable enough to keep open.