Merge branch 'master' into fix-get-mapping-head

* master: (1210 commits)
  Add support for clear scroll to high level REST client (elastic#25038)
  Tiny correction in inner-hits.asciidoc (elastic#25066)
  Added release notes for 6.0.0-alpha2
  Expand index expressions against indices only when managing aliases (elastic#23997)
  Collapse inner hits rest test should not skip 5.x
  Settings: Fix secure settings by prefix (elastic#25064)
  add `exclude_keys` option to KeyValueProcessor (elastic#24876)
  Test: update missing body tests to run against versions >= 5.5.0
  Track EWMA[1] of task execution time in search threadpool executor
  Removes an invalid assert in resizing big arrays which does not always hold (resizing can result in a smaller size than the current size, while the assert attempted to verify the new size is always greater than the current).
  Fixed NPEs caused by requests without content. (elastic#23497)
  Plugins can register pre-configured char filters (elastic#25000)
  Build: Allow preserving shared dir (elastic#24962)
  Tests: Make secure settings available from settings builder for tests (elastic#25037)
  [TEST] Skip wildcard expansion test due to breaking change
  Test that gradle and Java version types match (elastic#24943)
  Include duplicate jar when jarhell check fails
  Change ScriptContexts to use needs instead of uses$. (elastic#25036)
  Change `has_child`, `has_parent` queries and `childen` aggregation to work with the new join field type and at the same time maintaining support for the `_parent` meta field type.
  Remove comma-separated feature parsing for GetIndicesAction
  ...

Author: jasontedor

.github/ISSUE_TEMPLATE.md

@@ -1,40 +1,46 @@
 <!--
-GitHub is reserved for bug reports and feature requests. The best place
-to ask a general question is at the Elastic Discourse forums at
-https://discuss.elastic.co. If you are in fact posting a bug report or
-a feature request, please include one and only one of the below blocks
-in your new issue. Note that whether you're filing a bug report or a
-feature request, ensure that your submission is for an
-[OS that we support](https://www.elastic.co/support/matrix#show_os).
-Bug reports on an OS that we do not support or feature requests
-specific to an OS that we do not support will be closed.
--->
 
-<!--
-If you are filing a bug report, please remove the below feature
-request block and provide responses for all of the below items.
+** Please read the guidelines below. **
+
+Issues that do not follow these guidelines are likely to be closed.
+
+1.  GitHub is reserved for bug reports and feature requests. The best place to
+    ask a general question is at the Elastic [forums](https://discuss.elastic.co).
+    GitHub is not the place for general questions.
+
+2.  Is this bug report or feature request for a supported OS? If not, it
+    is likely to be closed.  See https://www.elastic.co/support/matrix#show_os
+
+3.  Please fill out EITHER the feature request block or the bug report block
+    below, and delete the other block.
+
 -->
 
+<!-- Feature request -->
+
+**Describe the feature**:
+
+<!-- Bug report -->
+
 **Elasticsearch version**:
 
 **Plugins installed**: []
 
-**JVM version**:
+**JVM version** (`java -version`):
 
-**OS version**:
+**OS version** (`uname -a` if on a Unix-like system):
 
 **Description of the problem including expected versus actual behavior**:
 
 **Steps to reproduce**:
+
+Please include a *minimal* but *complete* recreation of the problem, including
+(e.g.) index creation, mappings, settings, query etc.  The easier you make for
+us to reproduce it, the more likely that somebody will take the time to look at it.
+
  1.
  2.
  3.
 
 **Provide logs (if relevant)**:
 
-<!--
-If you are filing a feature request, please remove the above bug
-report block and provide responses for all of the below items.
--->
-
-**Describe the feature**:

.github/PULL_REQUEST_TEMPLATE.md

@@ -11,3 +11,4 @@ attention.
 - If submitting code, have you built your formula locally prior to submission with `gradle check`?
 - If submitting code, is your pull request against master? Unless there is a good reason otherwise, we prefer pull requests against master and will backport as needed.
 - If submitting code, have you checked that your submission is for an [OS that we support](https://www.elastic.co/support/matrix#show_os)?
+- If you are submitting this code for a class then read our [policy](https://github.com/elastic/elasticsearch/blob/master/CONTRIBUTING.md#contributing-as-part-of-a-class) for that.

CONTRIBUTING.md

@@ -88,8 +88,8 @@ Contributing to the Elasticsearch codebase
 **Repository:** [https://github.com/elastic/elasticsearch](https://github.com/elastic/elasticsearch)
 
 Make sure you have [Gradle](http://gradle.org) installed, as
-Elasticsearch uses it as its build system. Gradle must be version 2.13 _exactly_ in
-order to build successfully.
+Elasticsearch uses it as its build system. Gradle must be at least
+version 3.3 in order to build successfully.
 
 Eclipse users can automatically configure their IDE: `gradle eclipse`
 then `File: Import: Existing Projects into Workspace`. Select the
@@ -101,7 +101,11 @@ IntelliJ users can automatically configure their IDE: `gradle idea`
 then `File->New Project From Existing Sources`. Point to the root of
 the source directory, select
 `Import project from external model->Gradle`, enable
-`Use auto-import`.
+`Use auto-import`. Additionally, in order to run tests directly from 
+IDEA 2017.1 and above it is required to disable IDEA run launcher, 
+which can be achieved by adding `-Didea.no.launcher=true` 
+[JVM option](https://intellij-support.jetbrains.com/hc/en-us/articles/206544869-Configuring-JVM-options-and-platform-properties) 
+
 
 The Elasticsearch codebase makes heavy use of Java `assert`s and the
 test runner requires that assertions be enabled within the JVM. This
@@ -139,3 +143,32 @@ Before submitting your changes, run the test suite to make sure that nothing is
 ```sh
 gradle check
 ```
+
+Contributing as part of a class
+-------------------------------
+In general Elasticsearch is happy to accept contributions that were created as
+part of a class but strongly advise against making the contribution as part of
+the class. So if you have code you wrote for a class feel free to submit it.
+
+Please, please, please do not assign contributing to Elasticsearch as part of a
+class. If you really want to assign writing code for Elasticsearch as an
+assignment then the code contributions should be made to your private clone and
+opening PRs against the primary Elasticsearch clone must be optional, fully
+voluntary, not for a grade, and without any deadlines.
+
+Because:
+
+* While the code review process is likely very educational, it can take wildly
+varying amounts of time depending on who is available, where the change is, and
+how deep the change is. There is no way to predict how long it will take unless
+we rush.
+* We do not rush reviews without a very, very good reason. Class deadlines
+aren't a good enough reason for us to rush reviews.
+* We deeply discourage opening a PR you don't intend to work through the entire
+code review process because it wastes our time.
+* We don't have the capacity to absorb an entire class full of new contributors,
+especially when they are unlikely to become long time contributors.
+
+Finally, we require that you run `gradle check` before submitting a
+non-documentation contribution. This is mentioned above, but it is worth
+repeating in this section because it has come up in this context.

README.textile

@@ -200,7 +200,7 @@ We have just covered a very small portion of what Elasticsearch is all about. Fo
 
 h3. Building from Source
 
-Elasticsearch uses "Gradle":https://gradle.org for its build system. You'll need to have version 2.13 of Gradle installed.
+Elasticsearch uses "Gradle":https://gradle.org for its build system. You'll need to have at least version 3.3 of Gradle installed.
 
 In order to create a distribution, simply run the @gradle assemble@ command in the cloned directory.
 

TESTING.asciidoc

@@ -345,24 +345,23 @@ VM running trusty by running
 
 These are the linux flavors the Vagrantfile currently supports:
 
-* ubuntu-1204 aka precise
 * ubuntu-1404 aka trusty
 * ubuntu-1604 aka xenial
 * debian-8 aka jessie, the current debian stable distribution
 * centos-6
 * centos-7
-* fedora-24
+* fedora-25
 * oel-6 aka Oracle Enterprise Linux 6
 * oel-7 aka Oracle Enterprise Linux 7
 * sles-12
-* opensuse-13
+* opensuse-42 aka Leap
 
 We're missing the following from the support matrix because there aren't high
 quality boxes available in vagrant atlas:
 
 * sles-11
 
-We're missing the follow because our tests are very linux/bash centric:
+We're missing the following because our tests are very linux/bash centric:
 
 * Windows Server 2012
 
@@ -418,38 +417,58 @@ sudo -E bats $BATS_TESTS/*rpm*.bats
 If you wanted to retest all the release artifacts on a single VM you could:
 
 -------------------------------------------------
-gradle vagrantSetUp
-vagrant up ubuntu-1404 --provider virtualbox && vagrant ssh ubuntu-1404
+gradle setupBats
+cd qa/vagrant; vagrant up ubuntu-1404 --provider virtualbox && vagrant ssh ubuntu-1404
 cd $BATS_ARCHIVES
 sudo -E bats $BATS_TESTS/*.bats
 -------------------------------------------------
 
 You can also use Gradle to prepare the test environment and then starts a single VM:
 
 -------------------------------------------------
-gradle vagrantFedora24#up
+gradle vagrantFedora25#up
 -------------------------------------------------
 
-Or any of vagrantCentos6#up, vagrantDebian8#up, vagrantFedora24#up, vagrantOel6#up,
-vagrantOel7#up, vagrantOpensuse13#up, vagrantSles12#up, vagrantUbuntu1204#up,
-vagrantUbuntu1604#up.
+Or any of vagrantCentos6#up, vagrantCentos7#up, vagrantDebian8#up,
+vagrantFedora25#up, vagrantOel6#up, vagrantOel7#up, vagrantOpensuse13#up,
+vagrantSles12#up, vagrantUbuntu1404#up, vagrantUbuntu1604#up.
 
 Once up, you can then connect to the VM using SSH from the elasticsearch directory:
 
 -------------------------------------------------
-vagrant ssh fedora-24
+vagrant ssh fedora-25
 -------------------------------------------------
 
 Or from another directory:
 
 -------------------------------------------------
-VAGRANT_CWD=/path/to/elasticsearch vagrant ssh fedora-24
+VAGRANT_CWD=/path/to/elasticsearch vagrant ssh fedora-25
 -------------------------------------------------
 
 Note: Starting vagrant VM outside of the elasticsearch folder requires to
 indicates the folder that contains the Vagrantfile using the VAGRANT_CWD
 environment variable.
 
+== Testing backwards compatibility
+
+Backwards compatibility tests exist to test upgrading from each supported version
+to the current version. To run all backcompat tests use:
+
+-------------------------------------------------
+gradle bwcTest
+-------------------------------------------------
+
+A specific version can be tested as well. For example, to test backcompat with
+version 5.3.2 run:
+
+-------------------------------------------------
+gradle v5.3.2#bwcTest
+-------------------------------------------------
+
+When running `gradle check`, some minimal backcompat checks are run. Which version
+is tested depends on the branch. On master, this will test against the current
+stable branch. On the stable branch, it will test against the latest release
+branch. Finally, on a release branch, it will test against the most recent release.
 
 == Coverage analysis
 
@@ -505,4 +524,3 @@ included as part of the build by checking the projects of the build.
 ---------------------------------------------------------------------------
 gradle projects
 ---------------------------------------------------------------------------
-