fix script_name without / at beginning

[abtinmo]

What kind of change does this PR introduce?

• bug fix
• feature
• docs update
• tests/coverage improvement
• refactoring
• other

What is the related issue number (starting with #)

#1772

What is the current behavior? (You can also link to an open issue here)

#1772

What is the new behavior (if this is a feature change)?

1. shows an error, telling: script_name foo should start with /

2. fixes the script_name to prevent 404 error (not sure if it's necessary)

Other information:

Checklist:

• I think the code is well written
• I wrote good commit messages
• I have squashed related commits together after the changes have been approved
• Unit tests for the changes exist
• Integration tests for the changes exist (if applicable)
• I used the same coding conventions as the rest of the project
• The new code doesn't generate linter offenses
• Documentation reflects the changes
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences

[webknjaz]

Hey @abtinmo, thanks for the PR!

Please add a test for this change. And make sure the CI is green.

[codecov]

Codecov Report

Merging #1835 into master will decrease coverage by 2.89%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #1835     +/-   ##
=========================================
- Coverage   81.21%   78.31%   -2.9%     
=========================================
  Files         104      104             
  Lines       13625    13264    -361     
=========================================
- Hits        11065    10388    -677     
- Misses       2560     2876    +316

[abtinmo]

Hi @webknjaz,

it seems there is a problem with your macos config for ci.
and failed with AppVeyor is for #1750

[webknjaz]

@abtinmo don't worry Circle CI and that flaky test. Just add a test case for your change.

[abtinmo]

@webknjaz its done.

[webknjaz]

This change feels dangerous so I would also require a clear approval from @jaraco, not just myself.

[jaraco]

I'm disinclined to continue to let the user supply an erroneous value and correct it for them. Why not instead hard-fail (raise an exception) when invalid values are input (similar to how script_name=None is handled)?

[abtinmo]

fixes the script_name to prevent 404 error (not sure if it's necessary) , its what i said in my first comment.
i don't think letting user to continue is a right solution. but in doc i saw this:
This should start with a slash

so i choose to fix error myself and throw a console error.
raise an exception is indeed a better solution

[webknjaz]

AFAIR we discussed raising an exception for the invalid input. I'll wait for this change before attempting to review again.