manifest_xml: initial support for <superproject>

At most one superproject may be specified. It will be used
to specify the URL of superproject.

It would have 3 attributes: remote, name, and default.
Only "name" is required while the others have reasonable defaults.

<remote name="superproject-url" review="<url>" />
<superproject remote="superproject-url" name="platform/superproject"/>

TODO: This CL only implements the parsing logic and further work
will be in followup CLs.

Tested the code with the following commands.

$ ./run_tests tests/test_manifest_xml.py
$ ./run_tests -v

Bug: https://crbug.com/gerrit/13709
Tested-by: Raman Tenneti <rtenneti@google.com>
Change-Id: I5b4bba02c8b59601c754cf6b5e4d07a1e16ce167
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/292982
Reviewed-by: Mike Frysinger <vapier@google.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/docs/manifest-format.md b/docs/manifest-format.md
index ca385ba3..8e5e2874 100644
--- a/docs/manifest-format.md
+++ b/docs/manifest-format.md
@@ -29,6 +29,7 @@ following DTD:
                       project*,
                       extend-project*,
                       repo-hooks?,
+                      superproject?,
                       include*)>
 
   <!ELEMENT notice (#PCDATA)>
@@ -98,6 +99,10 @@ following DTD:
   <!ATTLIST repo-hooks in-project CDATA #REQUIRED>
   <!ATTLIST repo-hooks enabled-list CDATA #REQUIRED>
 
+  <!ELEMENT superproject (EMPTY)>
+  <!ATTLIST superproject name    CDATA #REQUIRED>
+  <!ATTLIST superproject remote  IDREF #IMPLIED>
+
   <!ELEMENT include EMPTY>
   <!ATTLIST include name   CDATA #REQUIRED>
   <!ATTLIST include groups CDATA #IMPLIED>
@@ -377,6 +382,28 @@ defined `project` element.
 
 Attribute `enabled-list`: List of hooks to use, whitespace or comma separated.
 
+### Element superproject
+
+***
+ *Note*: This is currently a WIP.
+***
+
+NB: See the [git superprojects documentation](
+https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects) for background
+information.
+
+This element is used to specify the URL of the superproject. It has "name" and
+"remote" as atrributes. Only "name" is required while the others have
+reasonable defaults. At most one superproject may be specified.
+Attempting to redefine it will fail to parse.
+
+Attribute `name`: A unique name for the superproject. This attribute has the
+same meaning as project's name attribute. See the
+[element project](#element-project) for more information.
+
+Attribute `remote`: Name of a previously defined remote element.
+If not supplied the remote given by the default element is used.
+
 ### Element include
 
 This element provides the capability of including another manifest