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 <body class="article">
 <div id="header">
 <h1>Trivial merge rules</h1>
 </div>
 <div id="content">
 <div id="preamble">
 <div class="sectionbody">
 <div class="paragraph"><p>This document describes the outcomes of the trivial merge logic in read-tree.</p></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_one_way_merge">One-way merge</h2>
 <div class="sectionbody">
 <div class="paragraph"><p>This replaces the index with a different tree, keeping the stat info
 for entries that don&#8217;t change, and allowing -u to make the minimum
 required changes to the working tree to have it match.</p></div>
 <div class="paragraph"><p>Entries marked <em>+</em> have stat information. Spaces marked <em>*</em> don&#8217;t
 affect the result.</p></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>index tree result
 -----------------------
 * (empty) (empty)
 (empty) tree tree
 index+ tree tree
 index+ index index+</code></pre>
 </div></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_two_way_merge">Two-way merge</h2>
 <div class="sectionbody">
 <div class="paragraph"><p>It is permitted for the index to lack an entry; this does not prevent
 any case from applying.</p></div>
 <div class="paragraph"><p>If the index exists, it is an error for it not to match either the old
 or the result.</p></div>
 <div class="paragraph"><p>If multiple cases apply, the one used is listed first.</p></div>
 <div class="paragraph"><p>A result which changes the index is an error if the index is not empty
 and not up-to-date.</p></div>
 <div class="paragraph"><p>Entries marked <em>+</em> have stat information. Spaces marked <em>*</em> don&#8217;t
 affect the result.</p></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>case index old new result
 -------------------------------------
 0/2 (empty) * (empty) (empty)
 1/3 (empty) * new new
 4/5 index+ (empty) (empty) index+
 6/7 index+ (empty) index index+
 10 index+ index (empty) (empty)
 14/15 index+ old old index+
 18/19 index+ old index index+
 20 index+ index new new</code></pre>
 </div></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_three_way_merge">Three-way merge</h2>
 <div class="sectionbody">
 <div class="paragraph"><p>It is permitted for the index to lack an entry; this does not prevent
 any case from applying.</p></div>
 <div class="paragraph"><p>If the index exists, it is an error for it not to match either the
 head or (if the merge is trivial) the result.</p></div>
 <div class="paragraph"><p>If multiple cases apply, the one used is listed first.</p></div>
 <div class="paragraph"><p>A result of "no merge" means that index is left in stage 0, ancest in
 stage 1, head in stage 2, and remote in stage 3 (if any of these are
 empty, no entry is left for that stage). Otherwise, the given entry is
 left in stage 0, and there are no other entries.</p></div>
 <div class="paragraph"><p>A result of "no merge" is an error if the index is not empty and not
 up-to-date.</p></div>
 <div class="paragraph"><p><strong>empty</strong> means that the tree must not have a directory-file conflict
  with the entry.</p></div>
 <div class="paragraph"><p>For multiple ancestors, a <em>+</em> means that this case applies even if
 only one ancestor or remote fits; a <em>^</em> means all of the ancestors
 must be the same.</p></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>case ancest head remote result
 ----------------------------------------
 1 (empty)+ (empty) (empty) (empty)
 2ALT (empty)+ *empty* remote remote
 2 (empty)^ (empty) remote no merge
 3ALT (empty)+ head *empty* head
 3 (empty)^ head (empty) no merge
 4 (empty)^ head remote no merge
 5ALT * head head head
 6 ancest+ (empty) (empty) no merge
 8 ancest^ (empty) ancest no merge
 7 ancest+ (empty) remote no merge
 10 ancest^ ancest (empty) no merge
 9 ancest+ head (empty) no merge
 16 anc1/anc2 anc1 anc2 no merge
 13 ancest+ head ancest head
 14 ancest+ ancest remote remote
 11 ancest+ head remote no merge</code></pre>
 </div></div>
 <div class="paragraph"><p>Only #2ALT and #3ALT use <strong>empty</strong>, because these are the only cases
 where there can be conflicts that didn&#8217;t exist before. Note that we
 allow directory-file conflicts between things in different stages
 after the trivial merge.</p></div>
 <div class="paragraph"><p>A possible alternative for #6 is (empty), which would make it like
 #1. This is not used, due to the likelihood that it arises due to
 moving the file to multiple different locations or moving and deleting
 it in different branches.</p></div>
 <div class="paragraph"><p>Case #1 is included for completeness, and also in case we decide to
 put on <em>+</em> markings; any path that is never mentioned at all isn&#8217;t
 handled.</p></div>
 <div class="paragraph"><p>Note that #16 is when both #13 and #14 apply; in this case, we refuse
 the trivial merge, because we can&#8217;t tell from this data which is
 right. This is a case of a reverted patch (in some direction, maybe
 multiple times), and the right answer depends on looking at crossings
 of history or common ancestors of the ancestors.</p></div>
 <div class="paragraph"><p>Note that, between #6, #7, #9, and #11, all cases not otherwise
 covered are handled in this table.</p></div>
 <div class="paragraph"><p>For #8 and #10, there is alternative behavior, not currently
 implemented, where the result is (empty). As currently implemented,
 the automatic merge will generally give this effect.</p></div>
 </div>
 </div>
 </div>
 <div id="footnotes"><hr /></div>
 <div id="footer">
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	<div id="header">
	<h1>Trivial merge rules</h1>
	</div>
	<div id="content">
	<div id="preamble">
	<div class="sectionbody">
	<div class="paragraph"><p>This document describes the outcomes of the trivial merge logic in read-tree.</p></div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_one_way_merge">One-way merge</h2>
	<div class="sectionbody">
	<div class="paragraph"><p>This replaces the index with a different tree, keeping the stat info
	for entries that don’t change, and allowing -u to make the minimum
	required changes to the working tree to have it match.</p></div>
	<div class="paragraph"><p>Entries marked <em>+</em> have stat information. Spaces marked <em>*</em> don’t
	affect the result.</p></div>
	<div class="literalblock">
	<div class="content">
	<pre><code>index tree result
	-----------------------
	* (empty) (empty)
	(empty) tree tree
	index+ tree tree
	index+ index index+</code></pre>
	</div></div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_two_way_merge">Two-way merge</h2>
	<div class="sectionbody">
	<div class="paragraph"><p>It is permitted for the index to lack an entry; this does not prevent
	any case from applying.</p></div>
	<div class="paragraph"><p>If the index exists, it is an error for it not to match either the old
	or the result.</p></div>
	<div class="paragraph"><p>If multiple cases apply, the one used is listed first.</p></div>
	<div class="paragraph"><p>A result which changes the index is an error if the index is not empty
	and not up-to-date.</p></div>
	<div class="paragraph"><p>Entries marked <em>+</em> have stat information. Spaces marked <em>*</em> don’t
	affect the result.</p></div>
	<div class="literalblock">
	<div class="content">
	<pre><code>case index old new result
	-------------------------------------
	0/2 (empty) * (empty) (empty)
	1/3 (empty) * new new
	4/5 index+ (empty) (empty) index+
	6/7 index+ (empty) index index+
	10 index+ index (empty) (empty)
	14/15 index+ old old index+
	18/19 index+ old index index+
	20 index+ index new new</code></pre>
	</div></div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_three_way_merge">Three-way merge</h2>
	<div class="sectionbody">
	<div class="paragraph"><p>It is permitted for the index to lack an entry; this does not prevent
	any case from applying.</p></div>
	<div class="paragraph"><p>If the index exists, it is an error for it not to match either the
	head or (if the merge is trivial) the result.</p></div>
	<div class="paragraph"><p>If multiple cases apply, the one used is listed first.</p></div>
	<div class="paragraph"><p>A result of "no merge" means that index is left in stage 0, ancest in
	stage 1, head in stage 2, and remote in stage 3 (if any of these are
	empty, no entry is left for that stage). Otherwise, the given entry is
	left in stage 0, and there are no other entries.</p></div>
	<div class="paragraph"><p>A result of "no merge" is an error if the index is not empty and not
	up-to-date.</p></div>
	<div class="paragraph"><p><strong>empty</strong> means that the tree must not have a directory-file conflict
	with the entry.</p></div>
	<div class="paragraph"><p>For multiple ancestors, a <em>+</em> means that this case applies even if
	only one ancestor or remote fits; a <em>^</em> means all of the ancestors
	must be the same.</p></div>
	<div class="literalblock">
	<div class="content">
	<pre><code>case ancest head remote result
	----------------------------------------
	1 (empty)+ (empty) (empty) (empty)
	2ALT (empty)+ empty remote remote
	2 (empty)^ (empty) remote no merge
	3ALT (empty)+ head empty head
	3 (empty)^ head (empty) no merge
	4 (empty)^ head remote no merge
	5ALT * head head head
	6 ancest+ (empty) (empty) no merge
	8 ancest^ (empty) ancest no merge
	7 ancest+ (empty) remote no merge
	10 ancest^ ancest (empty) no merge
	9 ancest+ head (empty) no merge
	16 anc1/anc2 anc1 anc2 no merge
	13 ancest+ head ancest head
	14 ancest+ ancest remote remote
	11 ancest+ head remote no merge</code></pre>
	</div></div>
	<div class="paragraph"><p>Only #2ALT and #3ALT use <strong>empty</strong>, because these are the only cases
	where there can be conflicts that didn’t exist before. Note that we
	allow directory-file conflicts between things in different stages
	after the trivial merge.</p></div>
	<div class="paragraph"><p>A possible alternative for #6 is (empty), which would make it like
	#1. This is not used, due to the likelihood that it arises due to
	moving the file to multiple different locations or moving and deleting
	it in different branches.</p></div>
	<div class="paragraph"><p>Case #1 is included for completeness, and also in case we decide to
	put on <em>+</em> markings; any path that is never mentioned at all isn’t
	handled.</p></div>
	<div class="paragraph"><p>Note that #16 is when both #13 and #14 apply; in this case, we refuse
	the trivial merge, because we can’t tell from this data which is
	right. This is a case of a reverted patch (in some direction, maybe
	multiple times), and the right answer depends on looking at crossings
	of history or common ancestors of the ancestors.</p></div>
	<div class="paragraph"><p>Note that, between #6, #7, #9, and #11, all cases not otherwise
	covered are handled in this table.</p></div>
	<div class="paragraph"><p>For #8 and #10, there is alternative behavior, not currently
	implemented, where the result is (empty). As currently implemented,
	the automatic merge will generally give this effect.</p></div>
	</div>
	</div>
	</div>
	<div id="footnotes"><hr /></div>
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	Last updated 2013-08-20 08:40:27 PDT
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