Document has_many :extend option
Document has_many :extend option

https://github.com/rails/rails/commit/5937bd02dee112646469848d7fe8a8bfcef5b4c1#commitcomment-9205786

yhirano55/rails,alecspopa/rails,BlakeWilliams/rails,iainbeeston/rails,elfassy/rails,arjes/rails,Spin42/rails,joonyou/rails,vipulnsward/rails,MSP-Greg/rails,Envek/rails,palkan/rails,pvalena/rails,lucasmazza/rails,illacceptanything/illacceptanything,flanger001/rails,illacceptanything/illacceptanything,ledestin/rails,kmcphillips/rails,Erol/rails,yhirano55/rails,arunagw/rails,repinel/rails,joonyou/rails,kddeisz/rails,assain/rails,ngpestelos/rails,tgxworld/rails,yawboakye/rails,stefanmb/rails,rbhitchcock/rails,lcreid/rails,kddeisz/rails,kmayer/rails,coreyward/rails,utilum/rails,88rabbit/newRails,tjschuck/rails,illacceptanything/illacceptanything,xlymian/rails,Spin42/rails,bradleypriest/rails,shioyama/rails,assain/rails,ledestin/rails,yalab/rails,rbhitchcock/rails,voray/rails,xlymian/rails,matrinox/rails,Stellenticket/rails,ttanimichi/rails,joonyou/rails,mechanicles/rails,yahonda/rails,esparta/rails,sergey-alekseev/rails,elfassy/rails,georgeclaghorn/rails,gcourtemanche/rails,Envek/rails,BlakeWilliams/rails,yawboakye/rails,yasslab/railsguides.jp,starknx/rails,sergey-alekseev/rails,arunagw/rails,yawboakye/rails,marklocklear/rails,sealocal/rails,vipulnsward/rails,flanger001/rails,Erol/rails,kamipo/rails,illacceptanything/illacceptanything,bogdanvlviv/rails,maicher/rails,illacceptanything/illacceptanything,coreyward/rails,Edouard-chin/rails,illacceptanything/illacceptanything,richseviora/rails,ledestin/rails,Envek/rails,brchristian/rails,odedniv/rails,eileencodes/rails,elfassy/rails,flanger001/rails,mohitnatoo/rails,mohitnatoo/rails,sealocal/rails,notapatch/rails,rossta/rails,gauravtiwari/rails,illacceptanything/illacceptanything,tjschuck/rails,gfvcastro/rails,kirs/rails-1,kaspth/rails,arunagw/rails,gavingmiller/rails,kmcphillips/rails,jeremy/rails,eileencodes/rails,betesh/rails,MichaelSp/rails,MichaelSp/rails,mijoharas/rails,gfvcastro/rails,riseshia/railsguides.kr,prathamesh-sonpatki/rails,stefanmb/rails,fabianoleittes/rails,aditya-kapoor/rails,pschambacher/rails,kmayer/rails,palkan/rails,hanystudy/rails,alecspopa/rails,Edouard-chin/rails,yalab/rails,rossta/rails,schuetzm/rails,rafaelfranca/omg-rails,yalab/rails,MSP-Greg/rails,vassilevsky/rails,bradleypriest/rails,pvalena/rails,deraru/rails,odedniv/rails,ngpestelos/rails,maicher/rails,kenta-s/rails,kachick/rails,shioyama/rails,yhirano55/rails,kaspth/rails,illacceptanything/illacceptanything,kmayer/rails,schuetzm/rails,esparta/rails,koic/rails,MichaelSp/rails,travisofthenorth/rails,marklocklear/rails,kmcphillips/rails,amoody2108/TechForJustice,gfvcastro/rails,vipulnsward/rails,notapatch/rails,samphilipd/rails,travisofthenorth/rails,prathamesh-sonpatki/rails,mohitnatoo/rails,lcreid/rails,shioyama/rails,riseshia/railsguides.kr,starknx/rails,utilum/rails,utilum/rails,iainbeeston/rails,jeremy/rails,baerjam/rails,tjschuck/rails,hanystudy/rails,EmmaB/rails-1,Edouard-chin/rails,printercu/rails,mathieujobin/reduced-rails-for-travis,riseshia/railsguides.kr,bogdanvlviv/rails,felipecvo/rails,gcourtemanche/rails,kachick/rails,kirs/rails-1,kddeisz/rails,starknx/rails,betesh/rails,Vasfed/rails,mathieujobin/reduced-rails-for-travis,esparta/rails,brchristian/rails,riseshia/railsguides.kr,deraru/rails,yawboakye/rails,ttanimichi/rails,notapatch/rails,rafaelfranca/omg-rails,Vasfed/rails,88rabbit/newRails,yalab/rails,baerjam/rails,gauravtiwari/rails,mtsmfm/railstest,marklocklear/rails,Stellenticket/rails,iainbeeston/rails,schuetzm/rails,kamipo/rails,flanger001/rails,yahonda/rails,MSP-Greg/rails,yasslab/railsguides.jp,mechanicles/rails,amoody2108/TechForJustice,mtsmfm/rails,printercu/rails,eileencodes/rails,kmcphillips/rails,rails/rails,rbhitchcock/rails,illacceptanything/illacceptanything,lcreid/rails,odedniv/rails,georgeclaghorn/rails,BlakeWilliams/rails,mohitnatoo/rails,yhirano55/rails,illacceptanything/illacceptanything,tgxworld/rails,mtsmfm/rails,kenta-s/rails,mechanicles/rails,Stellenticket/rails,arunagw/rails,gfvcastro/rails,Sen-Zhang/rails,baerjam/rails,pvalena/rails,samphilipd/rails,matrinox/rails,hanystudy/rails,samphilipd/rails,palkan/rails,stefanmb/rails,assain/rails,matrinox/rails,yasslab/railsguides.jp,xlymian/rails,mechanicles/rails,Erol/rails,voray/rails,fabianoleittes/rails,lucasmazza/rails,illacceptanything/illacceptanything,amoody2108/TechForJustice,richseviora/rails,koic/rails,lcreid/rails,printercu/rails,jeremy/rails,kaspth/rails,georgeclaghorn/rails,sealocal/rails,yahonda/rails,illacceptanything/illacceptanything,untidy-hair/rails,deraru/rails,kamipo/rails,prathamesh-sonpatki/rails,travisofthenorth/rails,gavingmiller/rails,felipecvo/rails,utilum/rails,mathieujobin/reduced-rails-for-travis,vipulnsward/rails,travisofthenorth/rails,printercu/rails,untidy-hair/rails,mtsmfm/railstest,richseviora/rails,eileencodes/rails,EmmaB/rails-1,bolek/rails,esparta/rails,ttanimichi/rails,tijwelch/rails,ngpestelos/rails,Stellenticket/rails,vassilevsky/rails,Erol/rails,pschambacher/rails,illacceptanything/illacceptanything,mijoharas/rails,aditya-kapoor/rails,repinel/rails,brchristian/rails,tijwelch/rails,palkan/rails,gauravtiwari/rails,rails/rails,gcourtemanche/rails,bradleypriest/rails,Sen-Zhang/rails,iainbeeston/rails,bolek/rails,baerjam/rails,tijwelch/rails,shioyama/rails,maicher/rails,rails/rails,fabianoleittes/rails,Envek/rails,betesh/rails,prathamesh-sonpatki/rails,joonyou/rails,koic/rails,arjes/rails,fabianoleittes/rails,bogdanvlviv/rails,tgxworld/rails,illacceptanything/illacceptanything,alecspopa/rails,untidy-hair/rails,rossta/rails,yahonda/rails,tjschuck/rails,arjes/rails,yasslab/railsguides.jp,aditya-kapoor/rails,vassilevsky/rails,illacceptanything/illacceptanything,sergey-alekseev/rails,Vasfed/rails,assain/rails,Sen-Zhang/rails,MSP-Greg/rails,gavingmiller/rails,betesh/rails,bolek/rails,tgxworld/rails,pvalena/rails,mtsmfm/railstest,untidy-hair/rails,felipecvo/rails,mijoharas/rails,coreyward/rails,aditya-kapoor/rails,kddeisz/rails,notapatch/rails,Edouard-chin/rails,88rabbit/newRails,schuetzm/rails,kachick/rails,EmmaB/rails-1,lucasmazza/rails,kirs/rails-1,mtsmfm/rails,kenta-s/rails,voray/rails,repinel/rails,rafaelfranca/omg-rails,jeremy/rails,pschambacher/rails,repinel/rails,Spin42/rails,deraru/rails,Vasfed/rails,BlakeWilliams/rails,rails/rails,georgeclaghorn/rails,bogdanvlviv/rails