Apply outgoing transitions when adding dependencies

TransitionMutators can always return "" from OutgoingVariation in
order to implement the equivalent of CreateLocalVariations - a
variation that doesn't affect which variation of dependencies is
selected.  The same need applies when creating the dependency after
the TransitionMutator.  Call OutgoingVariation on the parent module
when adding new dependencies unless the variation was explicitly
requested.

Bug: 319288033
Test: TestPostTransitionDeps
Flag: NONE
Change-Id: Iadb72a5a3f19579a6c1d34e3c7169ee9e2b53210

context.go

@@ -1872,34 +1872,46 @@ func (c *Context) findReverseDependency(module *moduleInfo, config any, destName
 	}}
 }
 
-// applyIncomingTransitions takes a variationMap being used to add a dependency on a module in a moduleGroup
-// and applies the IncomingTransition method of each completed TransitionMutator to modify the requested variation.
-// It finds a variant that existed before the TransitionMutator ran that is a subset of the requested variant to
-// use as the module context for IncomingTransition.
-func (c *Context) applyIncomingTransitions(config any, group *moduleGroup, variant variationMap, requestedVariations []Variation) {
+// applyTransitions takes a variationMap being used to add a dependency on a module in a moduleGroup
+// and applies the OutgoingTransition and IncomingTransition methods of each completed TransitionMutator to
+// modify the requested variation.  It finds a variant that existed before the TransitionMutator ran that is
+// a subset of the requested variant to use as the module context for IncomingTransition.
+func (c *Context) applyTransitions(config any, module *moduleInfo, group *moduleGroup, variant variationMap,
+	requestedVariations []Variation) {
 	for _, transitionMutator := range c.transitionMutators {
+		// Apply the outgoing transition if it was not explicitly requested.
+		explicitlyRequested := slices.ContainsFunc(requestedVariations, func(variation Variation) bool {
+			return variation.Mutator == transitionMutator.name
+		})
+		sourceVariation := variant[transitionMutator.name]
+		outgoingVariation := sourceVariation
+		if !explicitlyRequested {
+			ctx := &outgoingTransitionContextImpl{
+				transitionContextImpl{context: c, source: module, dep: nil, depTag: nil, config: config},
+			}
+			outgoingVariation = transitionMutator.mutator.OutgoingTransition(ctx, sourceVariation)
+		}
+
+		// Find an appropriate module to use as the context for the IncomingTransition.
 		appliedIncomingTransition := false
 		for _, inputVariant := range transitionMutator.inputVariants[group] {
 			if inputVariant.variant.variations.subsetOf(variant) {
-				sourceVariation := variant[transitionMutator.name]
-
+				// Apply the incoming transition.
 				ctx := &incomingTransitionContextImpl{
 					transitionContextImpl{context: c, source: nil, dep: inputVariant,
 						depTag: nil, config: config},
 				}
 
-				outgoingVariation := transitionMutator.mutator.IncomingTransition(ctx, sourceVariation)
-				variant[transitionMutator.name] = outgoingVariation
+				finalVariation := transitionMutator.mutator.IncomingTransition(ctx, outgoingVariation)
+				variant[transitionMutator.name] = finalVariation
 				appliedIncomingTransition = true
 				break
 			}
 		}
-		if !appliedIncomingTransition {
-			// The transition mutator didn't apply anything to the target module, remove the variation unless it
+		if !appliedIncomingTransition && !explicitlyRequested {
+			// The transition mutator didn't apply anything to the target variant, remove the variation unless it
 			// was explicitly requested when adding the dependency.
-			if !slices.ContainsFunc(requestedVariations, func(v Variation) bool { return v.Mutator == transitionMutator.name }) {
-				delete(variant, transitionMutator.name)
-			}
+			delete(variant, transitionMutator.name)
 		}
 	}
 }
@@ -1928,7 +1940,7 @@ func (c *Context) findVariant(module *moduleInfo, config any,
 		newVariant[v.Mutator] = v.Variation
 	}
 
-	c.applyIncomingTransitions(config, possibleDeps, newVariant, requestedVariations)
+	c.applyTransitions(config, module, possibleDeps, newVariant, requestedVariations)
 
 	check := func(variant variationMap) bool {
 		if far {
@@ -3002,7 +3014,7 @@ func (c *Context) runMutator(config interface{}, mutator *mutatorInfo,
 			// Update module group to contain newly split variants
 			if module.splitModules != nil {
 				if isTransitionMutator {
-					// For transition mutators, save the pre-split variant for reusing later in applyIncomingTransitions.
+					// For transition mutators, save the pre-split variant for reusing later in applyTransitions.
 					transitionMutatorInputVariants[group] = append(transitionMutatorInputVariants[group], module)
 				}
 				group.modules, i = spliceModules(group.modules, i, module.splitModules)

transition_test.go

@@ -180,7 +180,7 @@ func TestTransition(t *testing.T) {
 
 func TestPostTransitionDeps(t *testing.T) {
 	ctx, errs := testTransition(fmt.Sprintf(testTransitionBp,
-		`post_transition_deps: ["D:late", "E:d", "F"],`))
+		`post_transition_deps: ["C", "D:late", "E:d", "F"],`))
 	assertNoErrors(t, errs)
 
 	// Module A uses Split to create a and b variants
@@ -209,13 +209,13 @@ func TestPostTransitionDeps(t *testing.T) {
 
 	checkTransitionDeps(t, ctx, A_a, "B(a)", "C(a)")
 	checkTransitionDeps(t, ctx, A_b, "B(b)", "C(b)")
-	// Verify post-mutator dependencies added to B:
-	//  C(c) is a pre-mutator dependency
+	// Verify post-mutator dependencies added to B.  The first C(c) is a pre-mutator dependency.
+	//  C(c) was added by C and rewritten by OutgoingTransition on B
 	//  D(d) was added by D:late and rewritten by IncomingTransition on D
 	//  E(d) was added by E:d
 	//  F() was added by F, and ignored the existing variation on B
-	checkTransitionDeps(t, ctx, B_a, "C(c)", "D(d)", "E(d)", "F()")
-	checkTransitionDeps(t, ctx, B_b, "C(c)", "D(d)", "E(d)", "F()")
+	checkTransitionDeps(t, ctx, B_a, "C(c)", "C(c)", "D(d)", "E(d)", "F()")
+	checkTransitionDeps(t, ctx, B_b, "C(c)", "C(c)", "D(d)", "E(d)", "F()")
 	checkTransitionDeps(t, ctx, C_a, "D(d)")
 	checkTransitionDeps(t, ctx, C_b, "D(d)")
 	checkTransitionDeps(t, ctx, C_c, "D(d)")