Document how properties work in defaults modules.
Also remove an unused field in DefaultsModuleBase.
Test: m nothing
Test: Verify no diffs in ninja files:
<check out clean tree>
m nothing && shasum out/*.ninja | sort -k2 > before
<apply patch>
m nothing && shasum out/*.ninja | sort -k2 > after
diff before after
Bug: 112158820
Change-Id: Id819cea10f7af1603b4e4e1b14c0b49afcd0fecd
diff --git a/android/defaults.go b/android/defaults.go
index d4fbf48..e969adc 100644
--- a/android/defaults.go
+++ b/android/defaults.go
@@ -63,9 +63,28 @@
type DefaultsModuleBase struct {
DefaultableModuleBase
- defaultProperties []interface{}
}
+// The common pattern for defaults modules is to register separate instances of
+// the xxxProperties structs in the AddProperties calls, rather than reusing the
+// ones inherited from Module.
+//
+// The effect is that e.g. myDefaultsModuleInstance.base().xxxProperties won't
+// contain the values that have been set for the defaults module. Rather, to
+// retrieve the values it is necessary to iterate over properties(). E.g. to get
+// the commonProperties instance that have the real values:
+//
+// d := myModule.(Defaults)
+// for _, props := range d.properties() {
+// if cp, ok := props.(*commonProperties); ok {
+// ... access property values in cp ...
+// }
+// }
+//
+// The rationale is that the properties on a defaults module apply to the
+// defaultable modules using it, not to the defaults module itself. E.g. setting
+// the "enabled" property false makes inheriting modules disabled by default,
+// rather than disabling the defaults module itself.
type Defaults interface {
Defaultable
isDefaults() bool