Progress bar prints each update on a new line

[irfinnew]

Note that this bug is not fixed by #4317, it has a different cause.

The erratic behaviour, on Yarn 1.1.0, NodeJS v6.11.4, Debian 9.1, rxvt terminal emulator (TERM=rxvt):

Strace shows that Yarn prints the progress bar without any control characters such as \r (in fact, not even \n, so technically all updates are on one huge line...):

22145 write(2, "[--------------------------------------------------------------------------------------------------------------------------] 0/1138", 131) = 131
22145 write(2, "[--------------------------------------------------------------------------------------------------------------------------] 3/1138", 131) = 131
22145 write(2, "[#-------------------------------------------------------------------------------------------------------------------------] 5/1138", 131) = 131
22145 write(2, "[#-------------------------------------------------------------------------------------------------------------------------] 7/1138", 131 <unfinished ...>

After some prodding and poking, I found out that Yarn does print the progress bar properly when the COLORTERM environment variable is set:

Strace reveals that in this case, Yarn is emitting control characters, in a separate write (why not simply \r instead of ^[[1G? Ehh...):

22401 write(2, "[--------------------------------------------------------------------------------------------------------------------------] 0/1138", 131) = 131
22401 write(2, "\33[1G", 4)             = 4
22401 write(2, "[--------------------------------------------------------------------------------------------------------------------------] 3/1138", 131) = 131
22401 write(2, "\33[1G", 4 <unfinished ...>
22401 write(2, "[#-------------------------------------------------------------------------------------------------------------------------] 5/1138", 131) = 131
22401 write(2, "\33[1G", 4)             = 4
22401 write(2, "[#-------------------------------------------------------------------------------------------------------------------------] 7/1138", 131) = 131
22401 write(2, "\33[1G", 4)             = 4

But this environment variable is both optional and obsolete, so Yarn should not rely on it.

[BYK]

Ah, great find! Would you like to submit a PR and get your name in the commit history for both discovering and fixing this annoyance? :)

[irfinnew]

Hehe, nwholloway beat me to it :)

His fix works for me!

[arcanis]

Thanks anyway for letting us know :)