Merge branch 'jn/merge-renormalize'

* jn/merge-renormalize:
  merge-recursive --renormalize
  rerere: never renormalize
  rerere: migrate to parse-options API
  t4200 (rerere): modernize style
  ll-merge: let caller decide whether to renormalize
  ll-merge: make flag easier to populate
  Documentation/technical: document ll_merge
  merge-trees: let caller decide whether to renormalize
  merge-trees: push choice to renormalize away from low level
  t6038 (merge.renormalize): check that it can be turned off
  t6038 (merge.renormalize): try checkout -m and cherry-pick
  t6038 (merge.renormalize): style nitpicks
  Don't expand CRLFs when normalizing text during merge
  Try normalizing files to avoid delete/modify conflicts when merging
  Avoid conflicts when merging branches with mixed normalization

Conflicts:
	builtin/rerere.c
	t/t4200-rerere.sh

4 files changed, 129 insertions, 0 deletions

diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index 2e2370ccdb..e5a27d875e 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -317,6 +317,17 @@ command is "cat").
 	smudge = cat
 ------------------------
 
+For best results, `clean` should not alter its output further if it is
+run twice ("clean->clean" should be equivalent to "clean"), and
+multiple `smudge` commands should not alter `clean`'s output
+("smudge->smudge->clean" should be equivalent to "clean").  See the
+section on merging below.
+
+The "indent" filter is well-behaved in this regard: it will not modify
+input that is already correctly indented.  In this case, the lack of a
+smudge filter means that the clean filter _must_ accept its own output
+without modifying it.
+
 
 Interaction between checkin/checkout attributes
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -331,6 +342,29 @@ In the check-out codepath, the blob content is first converted
 with `text`, and then `ident` and fed to `filter`.
 
 
+Merging branches with differing checkin/checkout attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you have added attributes to a file that cause the canonical
+repository format for that file to change, such as adding a
+clean/smudge filter or text/eol/ident attributes, merging anything
+where the attribute is not in place would normally cause merge
+conflicts.
+
+To prevent these unnecessary merge conflicts, git can be told to run a
+virtual check-out and check-in of all three stages of a file when
+resolving a three-way merge by setting the `merge.renormalize`
+configuration variable.  This prevents changes caused by check-in
+conversion from causing spurious merge conflicts when a converted file
+is merged with an unconverted file.
+
+As long as a "smudge->clean" results in the same output as a "clean"
+even on files that are already smudged, this strategy will
+automatically resolve all filter-related conflicts.  Filters that do
+not act in this way may cause additional merge conflicts that must be
+resolved manually.
+
+
 Generating diff text
 ~~~~~~~~~~~~~~~~~~~~
 
diff --git a/Documentation/merge-config.txt b/Documentation/merge-config.txt
index a403155052..b72f533970 100644
--- a/Documentation/merge-config.txt
+++ b/Documentation/merge-config.txt
@@ -15,6 +15,16 @@ merge.renameLimit::
 	during a merge; if not specified, defaults to the value of
 	diff.renameLimit.
 
+merge.renormalize::
+	Tell git that canonical representation of files in the
+	repository has changed over time (e.g. earlier commits record
+	text files with CRLF line endings, but recent ones use LF line
+	endings).  In such a repository, git can convert the data
+	recorded in commits to a canonical form before performing a
+	merge to reduce unnecessary conflicts.  For more information,
+	see section "Merging branches with differing checkin/checkout
+	attributes" in linkgit:gitattributes[5].
+
 merge.stat::
 	Whether to print the diffstat between ORIG_HEAD and the merge result
 	at the end of the merge.  True by default.
diff --git a/Documentation/merge-strategies.txt b/Documentation/merge-strategies.txt
index a5bc1dbb95..049313d601 100644
--- a/Documentation/merge-strategies.txt
+++ b/Documentation/merge-strategies.txt
@@ -40,6 +40,18 @@ the other tree did, declaring 'our' history contains all that happened in it.
 theirs;;
 	This is opposite of 'ours'.
 
+renormalize;;
+	This runs a virtual check-out and check-in of all three stages
+	of a file when resolving a three-way merge.  This option is
+	meant to be used when merging branches with different clean
+	filters or end-of-line normalization rules.  See "Merging
+	branches with differing checkin/checkout attributes" in
+	linkgit:gitattributes[5] for details.
+
+no-renormalize;;
+	Disables the `renormalize` option.  This overrides the
+	`merge.renormalize` configuration variable.
+
 subtree[=path];;
 	This option is a more advanced form of 'subtree' strategy, where
 	the strategy makes a guess on how two trees must be shifted to
diff --git a/Documentation/technical/api-merge.txt b/Documentation/technical/api-merge.txt
new file mode 100644
index 0000000000..a7e050bb7a
--- /dev/null
+++ b/Documentation/technical/api-merge.txt
@@ -0,0 +1,73 @@
+merge API
+=========
+
+The merge API helps a program to reconcile two competing sets of
+improvements to some files (e.g., unregistered changes from the work
+tree versus changes involved in switching to a new branch), reporting
+conflicts if found.  The library called through this API is
+responsible for a few things.
+
+ * determining which trees to merge (recursive ancestor consolidation);
+
+ * lining up corresponding files in the trees to be merged (rename
+   detection, subtree shifting), reporting edge cases like add/add
+   and rename/rename conflicts to the user;
+
+ * performing a three-way merge of corresponding files, taking
+   path-specific merge drivers (specified in `.gitattributes`)
+   into account.
+
+Low-level (single file) merge
+-----------------------------
+
+`ll_merge`::
+
+	Perform a three-way single-file merge in core.  This is
+	a thin wrapper around `xdl_merge` that takes the path and
+	any merge backend specified in `.gitattributes` or
+	`.git/info/attributes` into account.  Returns 0 for a
+	clean merge.
+
+The caller:
+
+1. allocates an mmbuffer_t variable for the result;
+2. allocates and fills variables with the file's original content
+   and two modified versions (using `read_mmfile`, for example);
+3. calls ll_merge();
+4. reads the output from result_buf.ptr and result_buf.size;
+5. releases buffers when finished (free(ancestor.ptr); free(ours.ptr);
+   free(theirs.ptr); free(result_buf.ptr);).
+
+If the modifications do not merge cleanly, `ll_merge` will return a
+nonzero value and `result_buf` will generally include a description of
+the conflict bracketed by markers such as the traditional `<<<<<<<`
+and `>>>>>>>`.
+
+The `ancestor_label`, `our_label`, and `their_label` parameters are
+used to label the different sides of a conflict if the merge driver
+supports this.
+
+The `flag` parameter is a bitfield:
+
+ - The `LL_OPT_VIRTUAL_ANCESTOR` bit indicates whether this is an
+   internal merge to consolidate ancestors for a recursive merge.
+
+ - The `LL_OPT_FAVOR_MASK` bits allow local conflicts to be automatically
+   resolved in favor of one side or the other (as in 'git merge-file'
+   `--ours`/`--theirs`/`--union`).
+   They can be populated by `create_ll_flag`, whose argument can be
+   `XDL_MERGE_FAVOR_OURS`, `XDL_MERGE_FAVOR_THEIRS`, or
+   `XDL_MERGE_FAVOR_UNION`.
+
+Everything else
+---------------
+
+Talk about <merge-recursive.h> and merge_file():
+
+ - merge_trees() to merge with rename detection
+ - merge_recursive() for ancestor consolidation
+ - try_merge_command() for other strategies
+ - conflict format
+ - merge options
+
+(Daniel, Miklos, Stephan, JC)