terraform/diff/resource_builder.go

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package diff
import (
"github.com/hashicorp/terraform/terraform"
)
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// ResourceBuilder is a helper that can knows about how a single resource
// changes and how those changes affect the diff.
type ResourceBuilder struct {
CreateComputedAttrs []string
RequiresNewAttrs []string
}
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// Diff returns the ResourceDiff for a resource given its state and
// configuration.
func (b *ResourceBuilder) Diff(
s *terraform.ResourceState,
c *terraform.ResourceConfig) (*terraform.ResourceDiff, error) {
attrs := make(map[string]*terraform.ResourceAttrDiff)
requiresNewSet := make(map[string]struct{})
for _, k := range b.RequiresNewAttrs {
requiresNewSet[k] = struct{}{}
}
// We require a new resource if the ID is empty. Or, later, we set
// this to true if any configuration changed that triggers a new resource.
requiresNew := s.ID == ""
// Go through the configuration and find the changed attributes
for k, v := range c.Raw {
newV := v.(string)
var oldV string
var ok bool
if oldV, ok = s.Attributes[k]; ok {
// Old value exists! We check to see if there is a change
if oldV == newV {
continue
}
}
// There has been a change. Record it
attrs[k] = &terraform.ResourceAttrDiff{
Old: oldV,
New: newV,
}
// If this requires a new resource, record that and flag our
// boolean.
if _, ok := requiresNewSet[k]; ok {
attrs[k].RequiresNew = true
requiresNew = true
}
}
// If we require a new resource, then process all the attributes
// that will be changing due to the creation of the resource.
if requiresNew {
attrs["id"] = &terraform.ResourceAttrDiff{
Old: s.ID,
NewComputed: true,
RequiresNew: true,
}
for _, k := range b.CreateComputedAttrs {
old := s.Attributes[k]
attrs[k] = &terraform.ResourceAttrDiff{
Old: old,
NewComputed: true,
}
}
}
// Build our resulting diff if we had attributes change
var result *terraform.ResourceDiff
if len(attrs) > 0 {
result = &terraform.ResourceDiff{
Attributes: attrs,
}
}
return result, nil
}