Add runtime templating in configuration - #242

This PR is an attempt to partially fix #158 and superseded #181

Runtime templating

It allows templating configuration based on runtime information.
The function "pipeline" accepts one parameter where the value corresponds to a updatecli configuration key, a value where the key is case insensitive.

which can be defined like:

title: {{ pipeline "Source.Output" }}
sources:
default:
name: Get Latest helm release version
kind: githubRelease
spec:
owner: "helm"
repository: "helm"
token: {{ requiredEnv .github.token }}
username: olblak
version: latest

The configuration is updated after each stage, if it finds a function configuration value set to pipeline "updatecli_config", then it tries to replace with a value but only if the value exists otherwise it keeps pipeline "updatecli_config" for the next run .

While working on this PR, I took the following shortcuts

• the function pipeline can't be used for [sources, conditions, target] map key such as

title: {{ pipeline "Source.Output" }}
conditions:
  {{ pipeline "source.default":
    name: ...
    kind: githubRelease
    spec:
        ...

• I now mix context variable and global configuration, and I should split those two pieces of information into different variables such as sources.default.result should become context.sources.default.result
• We need a way to define resource order, because sources, conditions, and targets are maps, the order is not guaranteed so we can't reference source information from another source.

Depends_on

A depends_on key can be use to specify resources dependencies within a stage.
So in the following example the depends_on assume that we have another source with the id "weekly"
otherwise we fail the pipeline

sources:
  stable:
    kind: jenkins
    depends_on:
      - weekly
    name: Get Latest Jenkins stable version
    spec:
      github:
        token: {{ requiredEnv .github.token }}
        username: {{ .github.username }}

Errors

In case of a dependency loop detected, we return the following error

#########################
# RUNTIMETEMPLATING.TPL #
#########################

ERROR: Depency loop detected between Sources["weekly"] and Sources["stable"]
ERROR: ✗ dependency loop detected

In case of a wrong depends_on

#########################
# RUNTIMETEMPLATING.TPL #
#########################

ERROR: no valid depends_on value:"weeklyy"
ERROR: ✗ no valid depends_on value

Signed-off-by: Olivier Vernin olivier@vernin.me