Move description of --diff-merges option from git-log.txt to
diff-options.txt so that it is included in the git-show help.

While we are at it, make git-show closer to git-log in this area by
providing similar wording in the introduction of diff options.

Signed-off-by: Sergey Organov <redacted>
---
 Documentation/diff-options.txt | 54 ++++++++++++++++++++++++++++++++++
 Documentation/git-log.txt      | 52 --------------------------------
 Documentation/git-show.txt     |  8 +++--
 3 files changed, 60 insertions(+), 54 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 573fb9bb71e2..f1629887103e 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt

@@ -33,6 +33,60 @@ endif::git-diff[]
        show the patch by default, or to cancel the effect of `--patch`.
 endif::git-format-patch[]

+ifdef::git-log[]
+Note that unless one of `--diff-merges` variants (including short
+`-m`, `-c`, and `--cc` options) is explicitly given, merge commits
+will not show a diff, even if a diff format like `--patch` is
+selected, nor will they match search options like `-S`. The exception
+is when `--first-parent` is in use, in which case
+`--diff-merges=first-parent` is implied.

+
+--diff-merges=(off|none|first-parent|separate|combined|dense-combined)::
+--no-diff-merges::
+       Specify diff format to be used for merge commits. This has no
+       effect unless diff output is enabled in the first place (e.g.,
+       with `--patch` option.)
++
+--diff-merges=(off|none):::
+--no-diff-merges:::
+       (default) Disable output of diffs for merge commits. Useful to
+       override implied value.
++
+--diff-merges=first-parent:::
+       This option makes merge commits show the full diff with
+       respect to the first parent only, exactly like  regular
+       commits.
++
+--diff-merges=separate:::
+-m:::
+       This makes merge commits show the full diff with respect to
+       each of the parents. Separate log entry and diff is generated
+       for each parent.
++
+--diff-merges=combined:::
+-c:::
+       With this option, diff output for a merge commit shows the
+       differences from each of the parents to the merge result
+       simultaneously instead of showing pairwise diff between a
+       parent and the result one at a time. Furthermore, it lists
+       only files which were modified from all parents.
++
+--diff-merges=dense-combined:::
+--cc:::
+       With this option the output produced by
+       `--diff-merges=combined` is further compressed by omitting
+       uninteresting hunks whose contents in the parents have only
+       two variants and the merge result picks one of them without
+       modification.
+
+--combined-all-paths::
+       This flag causes combined diffs (used for merge commits) to
+       list the name of the file from all parents.  It thus only has
+       effect when `--diff-merges=[dense-]combined` is in use, and
+       is likely only useful if filename changes are detected (i.e.
+       when either rename or copy detection have been requested).
+endif::git-log[]
+
 -U<n>::
 --unified=<n>::
        Generate diffs with <n> lines of context instead of

diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index de498a189646..0cacc780bf30 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt

@@ -120,58 +120,6 @@ DIFF FORMATTING
 By default, `git log` does not generate any diff output. The options
 below can be used to show the changes made by each commit.

-Note that unless one of `--diff-merges` variants (including short
-`-m`, `-c`, and `--cc` options) is explicitly given, merge commits
-will not show a diff, even if a diff format like `--patch` is
-selected, nor will they match search options like `-S`. The exception
-is when `--first-parent` is in use, in which case
-`--diff-merges=first-parent` is implied.
-
---diff-merges=(off|none|first-parent|separate|combined|dense-combined)::
---no-diff-merges::
-       Specify diff format to be used for merge commits. This has no
-       effect unless diff output is enabled in the first place (e.g.,
-       with `--patch` option.)
-+
---diff-merges=(off|none):::
---no-diff-merges:::
-       (default) Disable output of diffs for merge commits. Useful to
-       override implied value.
-+
---diff-merges=first-parent:::
-       This option makes merge commits show the full diff with
-       respect to the first parent only, exactly like  regular
-       commits.
-+
---diff-merges=separate:::
--m:::
-       This makes merge commits show the full diff with respect to
-       each of the parents. Separate log entry and diff is generated
-       for each parent.
-+
---diff-merges=combined:::
--c:::
-       With this option, diff output for a merge commit shows the
-       differences from each of the parents to the merge result
-       simultaneously instead of showing pairwise diff between a
-       parent and the result one at a time. Furthermore, it lists
-       only files which were modified from all parents.
-+
---diff-merges=dense-combined:::
---cc:::
-       With this option the output produced by
-       `--diff-merges=combined` is further compressed by omitting
-       uninteresting hunks whose contents in the parents have only
-       two variants and the merge result picks one of them without
-       modification.
-
---combined-all-paths::
-       This flag causes combined diffs (used for merge commits) to
-       list the name of the file from all parents.  It thus only has
-       effect when `--diff-merges=[dense-]combined` is in use, and
-       is likely only useful if filename changes are detected (i.e.
-       when either rename or copy detection have been requested).
-

 :git-log: 1
 include::diff-options.txt[]

diff --git a/Documentation/git-show.txt b/Documentation/git-show.txt
index fcf528c1b30d..abe58ce5d3a8 100644
--- a/Documentation/git-show.txt
+++ b/Documentation/git-show.txt

@@ -45,8 +45,12 @@ include::pretty-options.txt[]
 include::pretty-formats.txt[]


-COMMON DIFF OPTIONS
--------------------
+DIFF FORMATTING
+---------------
+
+By default, `git show` does not generate any diff output. The options
+below can be used to show the changes made by each commit.
+