progress bar uses stderr instead of stdout

[Bezier89]

This appears to be a regression of #536

conda version : 4.5.0
conda-build version : 3.8.0
python version : 3.5.5.final.0
platform : win-64

Run a command such as follows:

conda create --yes -n TestEnv1 requests > stdout.txt 2> stderr.txt

Note that all the progress bar output goes into stderr.txt, while the rest goes into stdout.txt, as expected. Here's my stderr.txt:

win_inet_pton 1.0.1: | 0%
win_inet_pton 1.0.1: ########## | 100%

cffi 1.11.5: | 0%
cffi 1.11.5: #######5 | 75%
cffi 1.11.5: #########6 | 96%
cffi 1.11.5: ########## | 100%

pycparser 2.18: | 0%
pycparser 2.18: #######5 | 75%
pycparser 2.18: #########7 | 97%
pycparser 2.18: ########## | 100%

pip 9.0.3: | 0%
pip 9.0.3: #3 | 14%
pip 9.0.3: #####7 | 57%
pip 9.0.3: #######5 | 75%
pip 9.0.3: ########7 | 87%
pip 9.0.3: #########6 | 97%
pip 9.0.3: ########## | 100%

chardet 3.0.4: | 0%
chardet 3.0.4: #######5 | 75%
chardet 3.0.4: #########5 | 95%
chardet 3.0.4: ########## | 100%

six 1.11.0: | 0%
six 1.11.0: ########1 | 82%
six 1.11.0: ########## | 100%

vs2015_runtime 14.0.25420: | 0%
vs2015_runtime 14.0.25420: ###1 | 31%
vs2015_runtime 14.0.25420: #######5 | 75%
vs2015_runtime 14.0.25420: ########5 | 86%
vs2015_runtime 14.0.25420: #########5 | 95%
vs2015_runtime 14.0.25420: ########## | 100%

certifi 2018.1.18: | 0%
certifi 2018.1.18: ########8 | 88%
certifi 2018.1.18: ########## | 100%

openssl 1.0.2o: | 0%
openssl 1.0.2o: 1 | 2%
openssl 1.0.2o: #8 | 18%
openssl 1.0.2o: ###6 | 36%
openssl 1.0.2o: #####4 | 55%
openssl 1.0.2o: #######3 | 73%
openssl 1.0.2o: ########5 | 86%
openssl 1.0.2o: #########5 | 96%
openssl 1.0.2o: ########## | 100%

idna 2.6: | 0%
idna 2.6: #######8 | 79%
idna 2.6: ########## | 100%

asn1crypto 0.24.0: | 0%
asn1crypto 0.24.0: #######5 | 75%
asn1crypto 0.24.0: #########5 | 95%
asn1crypto 0.24.0: ########## | 100%

pysocks 1.6.8: | 0%
pysocks 1.6.8: ########## | 100%

cryptography 2.2.2: | 0%
cryptography 2.2.2: 2 | 2%
cryptography 2.2.2: #######5 | 75%
cryptography 2.2.2: #########3 | 93%
cryptography 2.2.2: ########## | 100%

urllib3 1.22: | 0%
urllib3 1.22: #######5 | 75%
urllib3 1.22: #########5 | 96%
urllib3 1.22: ########## | 100%

requests 2.18.4: | 0%
requests 2.18.4: #######7 | 77%
requests 2.18.4: ########## | 100%

python 3.6.5: | 0%
python 3.6.5: 2 | 3%
python 3.6.5: 7 | 7%
python 3.6.5: #2 | 12%
python 3.6.5: #6 | 17%
python 3.6.5: ##1 | 21%
python 3.6.5: ##5 | 26%
python 3.6.5: ### | 30%
python 3.6.5: ###4 | 35%
python 3.6.5: ###9 | 40%
python 3.6.5: ####4 | 44%
python 3.6.5: ####8 | 48%
python 3.6.5: #####2 | 53%
python 3.6.5: #####7 | 58%
python 3.6.5: ######2 | 62%
python 3.6.5: ######6 | 67%
python 3.6.5: #######1 | 71%
python 3.6.5: #######5 | 76%
python 3.6.5: #######8 | 79%
python 3.6.5: ########1 | 81%
python 3.6.5: ########2 | 83%
python 3.6.5: ########4 | 84%
python 3.6.5: ########5 | 85%
python 3.6.5: ########5 | 86%
python 3.6.5: ########6 | 87%
python 3.6.5: ########7 | 87%
python 3.6.5: ########7 | 88%
python 3.6.5: ########8 | 88%
python 3.6.5: ########8 | 89%
python 3.6.5: ########8 | 89%
python 3.6.5: ########9 | 89%
python 3.6.5: ########9 | 90%
python 3.6.5: ########9 | 90%
python 3.6.5: ######### | 90%
python 3.6.5: ######### | 91%
python 3.6.5: ######### | 91%
python 3.6.5: #########1 | 91%
python 3.6.5: #########1 | 92%
python 3.6.5: #########1 | 92%
python 3.6.5: #########2 | 92%
python 3.6.5: #########2 | 93%
python 3.6.5: #########2 | 93%
python 3.6.5: #########3 | 93%
python 3.6.5: #########3 | 93%
python 3.6.5: #########3 | 94%
python 3.6.5: #########4 | 94%
python 3.6.5: #########4 | 94%
python 3.6.5: #########4 | 95%
python 3.6.5: #########4 | 95%
python 3.6.5: #########5 | 95%
python 3.6.5: #########5 | 95%
python 3.6.5: #########5 | 96%
python 3.6.5: #########6 | 96%
python 3.6.5: #########6 | 96%
python 3.6.5: #########6 | 97%
python 3.6.5: #########6 | 97%
python 3.6.5: #########7 | 97%
python 3.6.5: #########7 | 97%
python 3.6.5: #########7 | 98%
python 3.6.5: #########7 | 98%
python 3.6.5: #########8 | 98%
python 3.6.5: #########8 | 98%
python 3.6.5: #########8 | 99%
python 3.6.5: #########8 | 99%
python 3.6.5: #########8 | 99%
python 3.6.5: #########9 | 99%
python 3.6.5: #########9 | 99%
python 3.6.5: #########9 | 100%
python 3.6.5: #########9 | 100%
python 3.6.5: #########9 | 100%
python 3.6.5: #########9 | 100%
python 3.6.5: ########## | 100%

pyopenssl 17.5.0: | 0%
pyopenssl 17.5.0: ########5 | 86%
pyopenssl 17.5.0: ########## | 100%

setuptools 39.0.1: | 0%
setuptools 39.0.1: #######5 | 75%
setuptools 39.0.1: ########9 | 89%
setuptools 39.0.1: ########## | 100%

ca-certificates 2018.03.07: | 0%
ca-certificates 2018.03.07: #######6 | 77%
ca-certificates 2018.03.07: ########## | 100%

wincertstore 0.2: | 0%
wincertstore 0.2: ########## | 100%

wheel 0.31.0: | 0%
wheel 0.31.0: ########5 | 86%
wheel 0.31.0: ########## | 100%

vc 14: | 0%
vc 14: ########## | 100%

[Bezier89]

PR: #7146

[kalefranz]

Can we elaborate on why we prefer progress bars and other UI elements (e.g. spinners) going to stdout? Just to make sure we’re all on the same page.

In general, we should take this opportunity to distinguish what we send to stdout vs what we send to stderr, and under what configuration conditions those change (e.g. json, quiet, or verbose flags).

[Bezier89]

@kalefranz As a rule of thumb, I would say that normal, expected things should go to stdout, and unexpected (not necessarily leading to a crash, but at least somehow interesting/noteworthy) things should go to stderr. Also that the number of lines written to stderr should be quite small, or else it makes finding actual errors cumbersome when they're preceded by hundreds of lines of progress bars!

[Bezier89]

@kalefranz Are there any objections to merging #7146? Seems like a simple fix.

[github-actions]

Hi there, thank you for your contribution to Conda!

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