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--- git_merge [2019/03/06 15:13] – [Query containedness and mergeness] rpjday
+++ git_merge [2019/03/13 13:09] (current) – [Global merge.ff option] rpjday
@@ Line 66: / Line 66: @@
              /          master
         D---E
+</code>
+or, depicted another way:
+<code>
+        D---E---A---B---C master
+                          topic
 </code>
@@ Line 226: / Line 233: @@
 Welcome to the second edition of the Pro Git book.
 ... etc ...
+</code>
+===== Advanced merging =====
+==== Fast-forwarding ====
+Recall a fast-forward merge:
+<code>
+              A---B---C topic
+             /          master
+        D---E
+</code>
+You may or may not want that:
+<code>
+--ff
+    When the merge resolves as a fast-forward, only update the
+    branch pointer, without creating a merge commit. This is
+    the default behavior.
+--no-ff
+    Create a merge commit even when the merge resolves as a
+    fast-forward. This is the default behaviour when merging an
+    annotated (and possibly signed) tag that is not stored in
+    its natural place in refs/tags/ hierarchy.
+--ff-only
+    Refuse to merge and exit with a non-zero status unless the
+    current HEAD is already up to date or the merge can be
+    resolved as a fast-forward.
+</code>
+==== Committing ====
+<code>
+--commit, --no-commit
+    Perform the merge and commit the result. This option can be
+    used to override --no-commit.
+    With --no-commit perform the merge but pretend the merge
+    failed and do not autocommit, to give the user a chance to
+    inspect and further tweak the merge result before
+    committing.
+</code>
+==== Editing ====
+<code>
+--edit, -e, --no-edit
+    Invoke an editor before committing successful mechanical
+    merge to further edit the auto-generated merge message, so
+    that the user can explain and justify the merge. The
+    --no-edit option can be used to accept the auto-generated
+    message (this is generally discouraged). The --edit (or -e)
+    option is still useful if you are giving a draft message
+    with the -m option from the command line and want to edit
+    it in the editor.
+</code>
+==== Squashing ====
+<code>
+--squash, --no-squash
+    Produce the working tree and index state as if a real merge
+    happened (except for the merge information), but do not
+    actually make a commit, move the HEAD, or record
+    $GIT_DIR/MERGE_HEAD (to cause the next git commit command
+    to create a merge commit). This allows you to create a
+    single commit on top of the current branch whose effect is
+    the same as merging another branch (or more in case of an
+    octopus).
+    With --no-squash perform the merge and commit the result.
+    This option can be used to override --squash.
+</code>
+As in:
+<code>
+$ git checkout master
+$ git merge --squash <branch with many commits>
+$ git commit
+</code>
+===== Setting merge options =====
+==== Per-branch merge options ====
+From ''man git-config'', you can set (either locally or globally) //per-branch// merge options:
+<code>
+branch.<name>.mergeOptions
+    Sets default options for merging into branch <name>. The
+    syntax and supported options are the same as those of git-
+    merge(1), but option values containing whitespace
+    characters are currently not supported.
+</code>
+For example, if you wanted to prevent any fast-forward merges to any ''master'' branch across all of your repositories, you could:
+<code>
+$ git config --global branch.master.mergeOptions "--no-ff"
+</code>
+==== Global merge.ff option ====
+For merging, there is at least one repo-wide merge option you can set (see ''man git-merge''):
+<code>
+merge.ff
+    By default, Git does not create an extra merge commit when
+    merging a commit that is a descendant of the current
+    commit. Instead, the tip of the current branch is
+    fast-forwarded. When set to false, this variable tells Git
+    to create an extra merge commit in such a case (equivalent
+    to giving the --no-ff option from the command line). When
+    set to only, only such fast-forward merges are allowed
+    (equivalent to giving the --ff-only option from the command
+    line).
+</code>
+So for widespread fast-forward merge configuration:
+<code>
+$ git config --global merge.ff "true"
+</code>
+This setting is superseded by any per-branch fast-forward merge setting.
+===== Merge strategies =====
+==== ours ====
+Technically record a merge while totally ignoring its content -- for record-keeping.
+Example:
+<code>
+$ git checkout master
+$ git merge --strategy=ours <obsolete branch>
+</code>
+How to make ''master'' look exactly like ''develop'':
+<code>
+$ git checkout topic
+$ git merge -s ours master
+$ git checkout master
+$ git merge --ff-only topic
+</code>
+To do this for an arbitrary commit, create a temporary branch:
+<code>
+$ git checkout -b tempbranch <commit ID>
+$ git merge -s ours master
+$ git checkout master
+$ git merge --ff-only tempbranch
 </code>