Change merge mode default based on driver

The default merge mode is 'merge-resolve' because it has been observed
that it more closely matches the behavior of jgit in Gerrit (or, at
least it did the last time we looked into this).  The other drivers
are unlikely to use jgit and more likely to use the default git
merge strategy.

This change allows the default to differ based on the driver, and
changes the default for all non-gerrit drivers to 'merge'.

The implementation anticipates that we may want to add more granularity
in the future, so the API accepts a project as an argument, and in
the future, drivers could provide a per-project default (which they
may obtain from the remote code review system).  That is not implemented
yet.

This adds some extra data to the /projects endpoint in the REST api.
It is currently not easy (and perhaps not possible) to determine what a
project's merge mode is through the api.  This change adds a metadata
field to the output which will show the resulting value computed from
all of the project stanzas.  The project stanzas themselves may have
null values for the merge modes now, so the web app now protects against
that.

Change-Id: I9ddb79988ca08aba4662cd82124bd91e49fd053c

1 files changed, 3 insertions, 1 deletions

diff --git a/web/src/containers/project/ProjectVariant.jsx b/web/src/containers/project/ProjectVariant.jsx
index 51a093a32..36d2c09ce 100644
--- a/web/src/containers/project/ProjectVariant.jsx
+++ b/web/src/containers/project/ProjectVariant.jsx
@@ -22,7 +22,9 @@ function ProjectVariant(props) {
   const { tenant, variant } = props
   const rows = []
 
-  rows.push({label: 'Merge mode', value: variant.merge_mode})
+  if (variant.merge_mode) {
+    rows.push({label: 'Merge mode', value: variant.merge_mode})
+  }
 
   if (variant.templates.length > 0) {
     const templateList = (