add reset_then_reuse_values support to helm module (#802) (#917)

This is a backport of PR #802 as merged into main (00699ac).
SUMMARY
Starting with version 3.14.0, Helm supports --reset-then-reuse-values. As discussed on the original PR. This greatly improves on --reuse-values as it allows to avoid templates errors when new features are added to an upgraded chart.
Closes #803
ISSUE TYPE

Feature Pull Request

COMPONENT NAME
helm
ADDITIONAL INFORMATION
This PR is greatly 'inspired' by #575 and because I wasn't sure how I could provide additional tests for it, I actually copied those build previously for --reuse-values (as it is an improvement on this feature.

Reviewed-by: Bianca Henderson <beeankha@gmail.com>

plugins/modules/helm.py

@@ -145,6 +145,16 @@ options:
     required: false
     default: True
     version_added: 3.0.0
+  reset_then_reuse_values:
+    description:
+      - When upgrading package, reset the values to the ones built into the chart, apply the last release's values and merge in any overrides from
+        parameters O(release_values), O(values_files) or O(set_values).
+      - If O(reset_values) or O(reuse_values) is set to V(True), this is ignored.
+      - This feature requires helm diff >= 3.9.12.
+    type: bool
+    required: false
+    default: False
+    version_added: 6.0.0
 
 #Helm options
   disable_hook:
@@ -509,6 +519,7 @@ def deploy(
     set_value_args=None,
     reuse_values=None,
     reset_values=True,
+    reset_then_reuse_values=False,
 ):
     """
     Install/upgrade/rollback release chart
@@ -526,6 +537,17 @@ def deploy(
     if reuse_values is not None:
         deploy_command += " --reuse-values=" + str(reuse_values)
 
+    if reset_then_reuse_values:
+        helm_version = module.get_helm_version()
+        if LooseVersion(helm_version) < LooseVersion("3.14.0"):
+            module.fail_json(
+                msg="reset_then_reuse_values requires helm >= 3.14.0, current version is {0}".format(
+                    helm_version
+                )
+            )
+        else:
+            deploy_command += " --reset-then-reuse-values"
+
     if wait:
         deploy_command += " --wait"
         if wait_timeout is not None:
@@ -642,6 +664,7 @@ def helmdiff_check(
     set_value_args=None,
     reuse_values=None,
     reset_values=True,
+    reset_then_reuse_values=False,
 ):
     """
     Use helm diff to determine if a release would change by upgrading a chart.
@@ -676,6 +699,24 @@ def helmdiff_check(
     if reuse_values:
         cmd += " --reuse-values"
 
+    if reset_then_reuse_values:
+        helm_diff_version = get_plugin_version("diff")
+        helm_version = module.get_helm_version()
+        fail_msg = ""
+        if LooseVersion(helm_diff_version) < LooseVersion("3.9.12"):
+            fail_msg = "reset_then_reuse_values requires helm diff >= 3.9.12, current version is {0}\n".format(
+                helm_diff_version
+            )
+        if LooseVersion(helm_version) < LooseVersion("3.14.0"):
+            fail_msg += "reset_then_reuse_values requires helm >= 3.14.0, current version is {0}\n".format(
+                helm_version
+            )
+
+        if fail_msg:
+            module.fail_json(msg=fail_msg)
+        else:
+            cmd += " --reset-then-reuse-values"
+
     rc, out, err = module.run_helm_command(cmd)
     return (len(out.strip()) > 0, out.strip())
 
@@ -735,6 +776,7 @@ def argument_spec():
             set_values=dict(type="list", elements="dict"),
             reuse_values=dict(type="bool"),
             reset_values=dict(type="bool", default=True),
+            reset_then_reuse_values=dict(type="bool", default=False),
         )
     )
     return arg_spec
@@ -787,6 +829,7 @@ def main():
     set_values = module.params.get("set_values")
     reuse_values = module.params.get("reuse_values")
     reset_values = module.params.get("reset_values")
+    reset_then_reuse_values = module.params.get("reset_then_reuse_values")
 
     if update_repo_cache:
         run_repo_update(module)
@@ -883,6 +926,7 @@ def main():
                 set_value_args=set_value_args,
                 reuse_values=reuse_values,
                 reset_values=reset_values,
+                reset_then_reuse_values=reset_then_reuse_values,
             )
             changed = True
 
@@ -908,6 +952,7 @@ def main():
                     set_value_args,
                     reuse_values=reuse_values,
                     reset_values=reset_values,
+                    reset_then_reuse_values=reset_then_reuse_values,
                 )
                 if would_change and module._diff:
                     opt_result["diff"] = {"prepared": prepared}
@@ -943,6 +988,7 @@ def main():
                     set_value_args=set_value_args,
                     reuse_values=reuse_values,
                     reset_values=reset_values,
+                    reset_then_reuse_values=reset_then_reuse_values,
                 )
                 changed = True