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			When a series of patches for a topic-B depends on having topic-A,
the workflow to prepare the topic-B branch would look like this:
    $ git checkout -b topic-B main
    $ git merge --no-ff --no-edit topic-A
    $ git am <mbox-for-topic-B
When topic-A gets updated, recreating the first merge and rebasing
the rest of the topic-B, all on detached HEAD, is a useful
technique.  After updating topic-A with its new round of patches:
    $ git checkout topic-B
    $ prev=$(git rev-parse 'HEAD^{/^Merge branch .topic-A. into}')
    $ git checkout --detach $prev^1
    $ git merge --no-ff --no-edit topic-A
    $ git rebase --onto HEAD $prev @{-1}^0
    $ git checkout -B @{-1}
This will
 (0) check out the current topic-B.
 (1) find the previous merge of topic-A into topic-B.
 (2) detach the HEAD to the parent of the previous merge.
 (3) merge the updated topic-A to it.
 (4) reapply the patches to rebuild the rest of topic-B.
 (5) update topic-B with the result.
without contaminating the reflog of topic-B too much.  topic-B@{1}
is the "logically previous" state before topic-A got updated, for
example.  At (4), comparison (e.g. range-diff) between HEAD and
@{-1} is a meaningful way to sanity check the result, and the same
can be done at (5) by comparing topic-B and topic-B@{1}.
But there is one glitch.  The merge into the detached HEAD done in
the step (3) above gives us "Merge branch 'topic-A' into HEAD", and
does not say "into topic-B".
Teach the "--into-name=<branch>" option to "git merge" and its
underlying "git fmt-merge-message", to pretend as if we were merging
into <branch>, no matter what branch we are actually merging into,
when they prepare the merge message.  The pretend name honors the
usual "into <target>" suppression mechanism, which can be seen in
the tests added here.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
		
	
		
			
				
	
	
		
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| #ifndef FMT_MERGE_MSG_H
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| #define FMT_MERGE_MSG_H
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| 
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| #include "strbuf.h"
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| 
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| #define DEFAULT_MERGE_LOG_LEN 20
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| 
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| struct fmt_merge_msg_opts {
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| 	unsigned add_title:1,
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| 		credit_people:1;
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| 	int shortlog_len;
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| 	const char *into_name;
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| };
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| 
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| extern int merge_log_config;
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| int fmt_merge_msg_config(const char *key, const char *value, void *cb);
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| int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
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| 		  struct fmt_merge_msg_opts *);
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| 
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| 
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| #endif /* FMT_MERGE_MSG_H */
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