Merge branch 'jl/submodule-fetch-on-demand'

* jl/submodule-fetch-on-demand:
  fetch/pull: Describe --recurse-submodule restrictions in the BUGS section
  submodule update: Don't fetch when the submodule commit is already present
  fetch/pull: Don't recurse into a submodule when commits are already present
  Submodules: Add 'on-demand' value for the 'fetchRecurseSubmodule' option
  config: teach the fetch.recurseSubmodules option the 'on-demand' value
  fetch/pull: Add the 'on-demand' value to the --recurse-submodules option
  fetch/pull: recurse into submodules when necessary

Conflicts:
	builtin/fetch.c
	submodule.c

Documentation/config.txt

@@ -897,9 +897,13 @@ diff.wordRegex::
 	characters are *ignorable* whitespace.
 
 fetch.recurseSubmodules::
-	A boolean value which changes the behavior for fetch and pull, the
-	default is to not recursively fetch populated submodules unless
-	configured otherwise.
+	This option can be either set to a boolean value or to 'on-demand'.
+	Setting it to a boolean changes the behavior of fetch and pull to
+	unconditionally recurse into submodules when set to true or to not
+	recurse at all when set to false. When set to 'on-demand' (the default
+	value), fetch and pull will only recurse into a populated submodule
+	when its superproject retrieves a commit that updates the submodule's
+	reference.
 
 fetch.unpackLimit::
 	If the number of objects fetched over the git native
@@ -1823,7 +1827,7 @@ submodule.<name>.update::
 	linkgit:git-submodule[1] and linkgit:gitmodules[5] for details.
 
 submodule.<name>.fetchRecurseSubmodules::
-	This option can be used to enable/disable recursive fetching of this
+	This option can be used to control recursive fetching of this
 	submodule. It can be overridden by using the --[no-]recurse-submodules
 	command line option to "git fetch" and "git pull".
 	This setting will override that from in the linkgit:gitmodules[5]

Documentation/fetch-options.txt

@@ -65,14 +65,33 @@ ifndef::git-pull[]
 	specified with the remote.<name>.tagopt setting. See
 	linkgit:git-config[1].
 
---[no-]recurse-submodules::
-	This option controls if new commits of all populated submodules should
-	be fetched too (see linkgit:git-config[1] and linkgit:gitmodules[5]).
+--recurse-submodules[=yes|on-demand|no]::
+	This option controls if and under what conditions new commits of
+	populated submodules should be fetched too. It can be used as a
+	boolean option to completely disable recursion when set to 'no' or to
+	unconditionally recurse into all populated submodules when set to
+	'yes', which is the default when this option is used without any
+	value. Use 'on-demand' to only recurse into a populated submodule
+	when the superproject retrieves a commit that updates the submodule's
+	reference to a commit that isn't already in the local submodule
+	clone.
+
+--no-recurse-submodules::
+	Disable recursive fetching of submodules (this has the same effect as
+	using the '--recurse-submodules=no' option).
 
 --submodule-prefix=<path>::
 	Prepend <path> to paths printed in informative messages
 	such as "Fetching submodule foo".  This option is used
 	internally when recursing over submodules.
+
+--recurse-submodules-default=[yes|on-demand]::
+	This option is used internally to temporarily provide a
+	non-negative default value for the --recurse-submodules
+	option.  All other methods of configuring fetch's submodule
+	recursion (such as settings in linkgit:gitmodules[5] and
+	linkgit:git-config[1]) override this option, as does
+	specifying --[no-]recurse-submodules directly.
 endif::git-pull[]
 
 -u::

Documentation/git-fetch.txt

@@ -76,6 +76,15 @@ The `pu` branch will be updated even if it is does not fast-forward,
 because it is prefixed with a plus sign; `tmp` will not be.
 
 
+BUGS
+----
+Using --recurse-submodules can only fetch new commits in already checked
+out submodules right now. When e.g. upstream added a new submodule in the
+just fetched commits of the superproject the submodule itself can not be
+fetched, making it impossible to check out that submodule later without
+having to do a fetch again. This is expected to be fixed in a future git
+version.
+
 SEE ALSO
 --------
 linkgit:git-pull[1]

Documentation/git-pull.txt

@@ -84,7 +84,7 @@ must be given before the options meant for 'git fetch'.
 --verbose::
 	Pass --verbose to git-fetch and git-merge.
 
---[no-]recurse-submodules::
+--[no-]recurse-submodules[=yes|on-demand|no]::
 	This option controls if new commits of all populated submodules should
 	be fetched too (see linkgit:git-config[1] and linkgit:gitmodules[5]).
 	That might be necessary to get the data needed for merging submodule
@@ -220,6 +220,15 @@ If you tried a pull which resulted in a complex conflicts and
 would want to start over, you can recover with 'git reset'.
 
 
+BUGS
+----
+Using --recurse-submodules can only fetch new commits in already checked
+out submodules right now. When e.g. upstream added a new submodule in the
+just fetched commits of the superproject the submodule itself can not be
+fetched, making it impossible to check out that submodule later without
+having to do a fetch again. This is expected to be fixed in a future git
+version.
+
 SEE ALSO
 --------
 linkgit:git-fetch[1], linkgit:git-merge[1], linkgit:git-config[1]

Documentation/gitmodules.txt

@@ -45,12 +45,12 @@ submodule.<name>.update::
 	the '--merge' or '--rebase' options.
 
 submodule.<name>.fetchRecurseSubmodules::
-	This option can be used to enable/disable recursive fetching of this
+	This option can be used to control recursive fetching of this
 	submodule. If this option is also present in the submodules entry in
 	.git/config of the superproject, the setting there will override the
 	one found in .gitmodules.
 	Both settings can be overridden on the command line by using the
-	"--[no-]recurse-submodules" option to "git fetch" and "git pull"..
+	"--[no-]recurse-submodules" option to "git fetch" and "git pull".
 
 submodule.<name>.ignore::
 	Defines under what circumstances "git status" and the diff family show