Feat add candidate output

[pohlt]

Pull Request Check List

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

I'm currently struggling with installing packages from multiple repos and had the impression that the log output could be improved.
The PR adds some more log output (log level: DETAIL) about matching candidates and their origin. If no matching candidates could be found, the non-matching candidates are printed to give the user some idea what might have gone wrong.

[codecov-commenter]

Codecov Report

Merging #421 (9aed1e0) into master (bb01e47) will decrease coverage by 0.18%.
The diff coverage is 100.00%.

❗ Current head 9aed1e0 differs from pull request most recent head f6592c4. Consider uploading reports for the commit f6592c4 to get more accurate results

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
- Coverage   83.36%   83.17%   -0.19%     
==========================================
  Files          68       68              
  Lines        5289     5302      +13     
  Branches      937      942       +5     
==========================================
+ Hits         4409     4410       +1     
- Misses        609      620      +11     
- Partials      271      272       +1     

Flag	Coverage Δ
unittests	83.11% <100.00%> (-0.17%)	⬇️

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Impacted Files	Coverage Δ
pdm/models/candidates.py	85.47% <ø> (ø)
pdm/models/repositories.py	71.42% <100.00%> (+2.50%)	⬆️
pdm/models/in_process/__init__.py	72.72% <0.00%> (-12.13%)	⬇️
pdm/models/python.py	88.88% <0.00%> (-6.67%)	⬇️
pdm/models/environment.py	79.65% <0.00%> (-0.87%)	⬇️
pdm/project/core.py	88.85% <0.00%> (-0.84%)	⬇️

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[frostming]

What is the value if the candidate is from a file link(including VCS, remote file and local file)?

[pohlt]

Good question. I haven't tried and don't know. At least it doesn't break if comes_from is not set.

[frostming]

Just to make sure it displays a meaningful value not confusing

[pohlt]

For the cases you mentioned, pdm doesn't seem to go through the repository search. At least I wasn't able to get the candidate list output.

[frostming]

The UI needs more careful design, consider this:

1. What message should be written into the log file when verbose is off.
2. How many lines will be output to the screen and whether it is easy for users to see what is happening.
3. Any color formatting to improve the readability?
4. Should the output go to stderr or stdout?

And in fact, there is a redundant output level DEBUG that is never used in PDM. It can be activated with -vv but currently no message falls into this level.

[pohlt]

The UI needs more careful design, consider this:

1. What message should be written into the log file when verbose is off.
2. How many lines will be output to the screen and whether it is easy for users to see what is happening.
3. Any color formatting to improve the readability?
4. Should the output go to stderr or stdout?

And in fact, there is a redundant output level DEBUG that is never used in PDM. It can be activated with -vv but currently no message falls into this level.

If you give me your preferences on those topics, I'm happy to adapt the code. I also thought about using the DEBUG level. Might be the better choice.

[frostming]

Here is a output with the change of this PR:
log.txt

As you can see there are lots of duplicate lines that are not informative. I recommend only log failing cases here in find_matches and log the pinned candidate that is chosen by the resolver. You can do this by improving the output of pdm/resolver/reporters.py. The current output is poorly designed and lacks color emphasis.

[frostming]

You can log the unfiltered candidate list (length limited to top 10) when find_matches failed to find any.

[pohlt]

Here is a output with the change of this PR:
log.txt

As you can see there are lots of duplicate lines that are not informative. I recommend only log failing cases here in find_matches and log the pinned candidate that is chosen by the resolver. You can do this by improving the output of pdm/resolver/reporters.py. The current output is poorly designed and lacks color emphasis.

I don't understand the "lacks color emphasis" in context with logging the output to a file: We cannot use color there, right?
W.r.t. formatting I tried to be more compliant.

[frostming]

Here is a output with the change of this PR:
log.txt
As you can see there are lots of duplicate lines that are not informative. I recommend only log failing cases here in find_matches and log the pinned candidate that is chosen by the resolver. You can do this by improving the output of pdm/resolver/reporters.py. The current output is poorly designed and lacks color emphasis.

I don't understand the "lacks color emphasis" in context with logging the output to a file: We cannot use color there, right?
W.r.t. formatting I tried to be more compliant.

You are right, I turned verbose on so the output goes to stdout, improving the format is also good

[pohlt]

I'm going to filter out the duplicate lines. Please don't accept yet.
Ok, done.

[linw1995]

LGTM 💯

[frostming]

Thanks for contribution