gistfile1.txt

# courtesy of doener from git IRC channel. Thanks man!

A---B---C---D (master)
 \   \
  \   X---X (topicA)
   \
    X---X---X (topicB)

(integration branch is somewhere else...)

a) Reset "integration" to "master":

A---B---C---D (master) (integration)
 \   \
  \   X---X (topicA)
   \
    X---X---X (topicB)

b) Merge what you need to "integration" (--no-ff)

A---B---C---D (master)
 \   \       \
  \   \       Ma--Mb (integration)
   \   \     /   /
    \   X---X (topicA)
     \         /
      X---X---X (topicB)

c) test

d) eventually update "master"

"master" can be fast-forwarded to "integration", leading to:

A---B---C---D---Ma--Mb (master) (integration
 \   \         /   /
  \   \       /   /
   \   \     /   /
    \   X---X (topicA)
     \         /
      X---X---X (topicB)

While a --no-ff would mean:

A---B---C---D--------Mi (master)
 \   \       \      /
  \   \       Ma--Mb (integration)
   \   \     /   /
    \   X---X (topicA)
     \         /
      X---X---X (topicB)

# if the test suite isn't successfull, you don't reach step d) and go back to a), so the merges you did in b) get dropped again, and there's only exactly one merge per topic branch

# since you already do --no-ff merges when merging into "integration", master should be fast-forwarded, you already have the per-topic merges, you (usually) don't want yet another one on top

# integration is reset to master, and then only sees --no-ff merges, so there's nothing but merges in it, so a fast-forward adds nothing but merge commits to master

# you should always redo the integration branch from scratch, so you're free to choose what to integrate for this test run