Supress fatal message in CPP example build

[aLekSer]

There is no .git folder in Docker when make build on examples/cpp-simple.
variable.
Note that when running next command AGONES_VERSION set as it should:
make run-sdk-command SDK_FOLDER=cpp COMMAND=build

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug

/kind cleanup

What this PR does / Why we need it:

Which issue(s) this PR fixes:

Closes #1091

Special notes for your reviewer:

[agones-bot]

Build Succeeded 👏

Build Id: eec802ce-0f15-437d-bc34-e6ecab1de36e

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.8.0-e069123
• image: gcr.io/agones-images/agones-sdk:1.8.0-e069123
• image: gcr.io/agones-images/agones-ping:1.8.0-e069123
• Linux C++ SDK (build): agonessdk-1.8.0-e069123-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.8.0-e069123.zip

A preview of the website (the last 30 builds are retained):

• https://e069123-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1701/head:pr_1701 && git checkout pr_1701
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.8.0-e069123

[roberthbailey]

This looks reasonable to me (since the output is only used if the return code from the child process is 0).

@dsazonoff - you had some thoughts on #1091 so I wanted to see if you had opinions about this solution?

[roberthbailey]

/assign

[aLekSer]

And adding link to my latest comment on the ticket:
#1091 (comment)
This code actually updates agones_VERSION value, when we build CPP SDK itself, not with an example:

set(agones_VERSION 1.7.0)

[dsazonoff]

Original error message was produced because of missing .git folder. It is an output of a git describe --tags --abbrev=0 command, and actually it's not an error, from the build point of view.

@aLekSer solution looks good, I think it can be merged.

Possible improvements is to do next steps to fill the version variable:

1. Check for an existing environment variable "VERSION" and use it if possible.
2. Otherwise check if it's a git repo (we need to locate .git folder). If yes - get version from git as in existing code
3. Otherwise just do not specify a version

Pseudocode:

if (DEFINED $ENV{VERSION)
  set(AGONES_VERSION $ENV{VERSION)
else()
  # keep existing code, but set AGONES_VERSION only for successful git execution
  find_package(git...)
  if (git_FOUND ...)
   ...
  endif()
endif()

set(project_version_param)
if (DEFINED AGONES_VERSION)
  set(project_version_param VERSION ${AGONES_VERSION})
endif()

project( ... ${project_version_param })

P.S. I'll do a new PR if I'll have some free time.

[agones-bot]

Build Succeeded 👏

Build Id: 202fd934-b9e4-48ef-bec8-aeac6a6dde78

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.8.0-f6f3392
• image: gcr.io/agones-images/agones-sdk:1.8.0-f6f3392
• image: gcr.io/agones-images/agones-ping:1.8.0-f6f3392
• Linux C++ SDK (build): agonessdk-1.8.0-f6f3392-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.8.0-f6f3392.zip

A preview of the website (the last 30 builds are retained):

• https://f6f3392-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1701/head:pr_1701 && git checkout pr_1701
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.8.0-f6f3392

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aLekSer, roberthbailey

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