Fixing git double-commit history

Question 1

The command to accomplish that is:

git rebase -i HEAD~7

This will open up your editor with something like this:

pick f392171 Removed most clearfixs in templates
pick ba9dd9a Removed most clearfixs in templates
pick df71a27 Unew redirect logic
pick 79ce782 Merge branch 'develop' of github.com:xxx/xxx into develop
pick 1383070 Merge branch 'develop' of github.com:xxx/xxx into develop
...

Now you can tell git what to do with each commit. Let's keep the commit f392171, the one where we added our feature. We'll squash the following two commits into the first one - leaving us with one clean.

Change your file to this:

pick f392171 Removed most clearfixs in templates
squash ba9dd9a Removed most clearfixs in templates
pick df71a27 Unew redirect logic
pick 79ce782 Merge branch 'develop' of github.com:xxx/xxx into develop
squash 1383070 Merge branch 'develop' of github.com:xxx/xxx into develop

When you save and exit the editor, Git applies all two changes and then puts you back into the editor to merge the three commit messages:

# This is a combination of  commits.
# The first commit's message is:
Removed most clearfixs in templates

# This is the 2nd commit message:

Removed most clearfixs in templates

When done, save and quit your editor. Git will now squash the commits into one. All done!

Then you have to do

git push origin your-branch -f

to force your locally commits changes into remote branch.

Note: You have to do a squash to every duplicated commit.

Question 2

Answer by @VAIRIX is perfect but there are complex cases where duplicate commits doesn't appear adjacent to each other, so squashing won't help.

So taking below history, (assume a~ is duplicate of a)

 # h
 # g
 # f
 # c~
 # b~
 # a~
 # e
 # d
 # c
 # b
 # a

Command to follow: (as told in answer by @VAIRIX or below if you want to rebase with master) git rebase master -i (Better follow git rebase -i HEAD~n to avoid rebasing headache)

Now! 1) squash the repeated commits as below:

 pick h
 pick g
 pick f
 pick c~
 s b~
 s a~
 pick e
 pick d
 pick c
 pick b
 pick a

Now, this will squash your commits in c

 # h
 # g
 # f
 # c~ (having changes of a~ and b~)
 # e
 # d
 # c
 # b
 # a

In my case, c~ was anti-commit of c, so I just had to do the process again, but now instead of squash with s, I'm dropping the commit with d

 pick h
 pick g
 pick f
 d c~ (having changes of a~ and b~)
 pick e
 pick d
 pick c
 pick b
 pick a

Now, you history will remove all the duplicate commits. Now, you can compare with the origin branch you had using git diff which had duplicate commits against your this branch. There shouldn't be any diff if you did it perfectly.

This process might seem a little longer but you're assured that you didn't miss any commits.