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helper/schema: Add behaviour detail to various custom diff comments 

Added some more detailed comments to CustomizeDiff's comments. The new
comments detail how CustomizeDiff will be called in the event of
different scenarios like creating a new resource, diffing an existing
one, diffing an existing resource that has a change that requires a new
resource, and destroy/tainted resources.

Also added similar detail to ForceNew in ResourceDiff.

This should help mitigate any confusion that may come up when using
CustomizeDiff, especially in the ForceNew scenario when the second run
happens with no state.
This commit is contained in:
Chris Marchesi 2017-07-05 07:05:37 -07:00 committed by Martin Atkins
parent 5031767b93
commit 2c541e8c97
2 changed files with 30 additions and 2 deletions
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20
helper/schema/resource.go
View File

@ -90,7 +90,25 @@ type Resource struct {
// diff that has been created, diff values not controlled by configuration,
// or even veto the diff altogether and abort the plan. It is passed a
// *ResourceDiff, a structure similar to ResourceData but lacking most write
// functions, allowing the provider to customize the diff only.
// functions like Set, while introducing new functions that work with the
// diff such as SetNew, SetNewComputed, and ForceNew.
//
// The phases Terraform runs this in, and the state available via functions
// like Get and GetChange, are as follows:
//
// * New resource: One run with no state
// * Existing resource: One run with state
// * Existing resource, forced new: One run with state (before ForceNew),
// then one run without state (as if new resource)
// * Tainted resource: No runs (custom diff logic is skipped)
// * Destroy: No runs (standard diff logic is skipped on destroy diffs)
//
// This function needs to be resilient to support all scenarios.
//
// If this function needs to access external API resources, remember to flag
// the RequiresRefresh attribute mentioned below to ensure that
// -refresh=false is blocked when running plan or apply, as this means that
// this resource requires refresh-like behaviour to work effectively.
//
// For the most part, only computed fields can be customized by this
// function.

12
helper/schema/resource_diff.go
View File

@ -290,7 +290,17 @@ func (d *ResourceDiff) setDiff(key string, new interface{}, computed bool) error
}
// ForceNew force-flags ForceNew in the schema for a specific key, and
// re-calculates its diff. This function is a no-op/error if there is no diff.
// re-calculates its diff, effectively causing this attribute to force a new
// resource.
//
// Keep in mind that forcing a new resource will force a second run of the
// resource's CustomizeDiff function (with a new ResourceDiff) once the current
// one has completed. This second run is performed without state. This behavior
// will be the same as if a new resource is being created and is performed to
// ensure that the diff looks like the diff for a new resource as much as
// possible. CustomizeDiff should expect such a scenario and act correctly.
//
// This function is a no-op/error if there is no diff.
//
// Note that the change to schema is permanent for the lifecycle of this
// specific ResourceDiff instance.