Wrong dependency version derivation

[peterdemin]

pip-compile fails to derive dependency version if different versions of package C are required by different versions of package B with an older version of B derived in the first round.

Here is the example:

First round:

Latest version of package A==2 requires old package B==1
Latest version of package B requires C==2

Second round:

B==1 requires C==1

Third round

C==1,2 fails to resolve.

I simplified things, but here is actual output if you are interested:

$ pip-compile -vvv --output-file requirements.txt requirements.txt.in -rU | grep -e django-ncbi-auth -e ncbi-myncbi-account -e django-ncbi-admin
  django-ncbi-admin
  django-ncbi-auth
  found candidate django-ncbi-admin==2.0.3 (constraint was <any>)
  found candidate django-ncbi-auth==5.1 (constraint was <any>)
  django-ncbi-admin==2.0.3 not in cache, need to check index
  django-ncbi-admin==2.0.3  requires django-ncbi-auth~=4.4.0, django<1.10.0,>=1.7.0
  django-ncbi-auth==5.1 not in cache, need to check index
  django-ncbi-auth==5.1     requires django<1.10,>=1.7, ipcalc~=1.99, ncbi-myncbi-account~=6.0
  adding django-ncbi-auth~=4.4.0
  adding ncbi-myncbi-account~=6.0
  django-ncbi-admin
  django-ncbi-auth~=4.4.0
  ncbi-myncbi-account~=6.0
  found candidate django-ncbi-admin==2.0.3 (constraint was <any>)
  found candidate django-ncbi-auth==4.4 (constraint was ~=4.4.0)
  found candidate ncbi-myncbi-account==6.0 (constraint was ~=6.0)
  django-ncbi-admin==2.0.3  requires django-ncbi-auth~=4.4.0, django<1.10.0,>=1.7.0
  django-ncbi-auth==4.4 not in cache, need to check index
  django-ncbi-auth==4.4     requires django<1.10,>=1.7, ipcalc~=1.99, ncbi-myncbi-account~=5.0
  ncbi-myncbi-account==6.0 not in cache, need to check index
  ncbi-myncbi-account==6.0  requires lxml~=3.4, ncbi-tx~=5.0, six
  adding ncbi-myncbi-account~=5.0
  django-ncbi-admin
  django-ncbi-auth~=4.4.0
  ncbi-myncbi-account~=5.0,~=6.0
  found candidate django-ncbi-admin==2.0.3 (constraint was <any>)
  found candidate django-ncbi-auth==4.4 (constraint was ~=4.4.0)
Could not find a version that matches ncbi-myncbi-account~=5.0,~=6.0
Tried: 1.0, 1.1, 1.1, 2.0, 2.0.1, 2.0.1, 2.0.1.post11+f5a85a6, 3.0, 3.0, 4.0, 4.0, 5.0, 5.0, 6.0, 6.0

Expected result

I expected, that the requirements of chosen B==1 on C will override requirements from B==2.

Actual result

But currently, they are combined resulting in impossible version requirements.

[davidovich]

Can you verify if this is still the case in 1.8.1 ? I think I may have fixed your issue in #450. Thanks.

[peterdemin]

I confirm. Version 1.8.0 failed on my requirements.txt.in. But after upgrade to 1.8.1 pip-compile resolved dependencies correctly.
Nice work! Thanks!