Treat allowed_deps.txt source file as optional.

Not all branches have packages/common/module, which breaks the build
for them.

Bug: 179234385
Test: removed allowed_deps.txt && m apex-allowed-deps-check
Change-Id: I38f47c7200e1afbd899e29843d0214bef826fcf9

apex/apex_singleton.go

@@ -81,25 +81,35 @@ func (s *apexDepsInfoSingleton) GenerateBuildActions(ctx android.SingletonContex
 		}
 	})
 
-	allowedDeps := android.ExistentPathForSource(ctx, "packages/modules/common/build/allowed_deps.txt").Path()
-
+	allowedDepsSource := android.ExistentPathForSource(ctx, "packages/modules/common/build/allowed_deps.txt")
 	newAllowedDeps := android.PathForOutput(ctx, "apex", "depsinfo", "new-allowed-deps.txt")
-	ctx.Build(pctx, android.BuildParams{
-		Rule:   generateApexDepsInfoFilesRule,
-		Inputs: append(updatableFlatLists, allowedDeps),
-		Output: newAllowedDeps,
-	})
-
 	s.allowedApexDepsInfoCheckResult = android.PathForOutput(ctx, newAllowedDeps.Rel()+".check")
-	ctx.Build(pctx, android.BuildParams{
-		Rule:   diffAllowedApexDepsInfoRule,
-		Input:  newAllowedDeps,
-		Output: s.allowedApexDepsInfoCheckResult,
-		Args: map[string]string{
-			"allowed_deps":     allowedDeps.String(),
-			"new_allowed_deps": newAllowedDeps.String(),
-		},
-	})
+
+	if !allowedDepsSource.Valid() {
+		// Unbundled projects may not have packages/modules/common/ checked out; ignore those.
+		ctx.Build(pctx, android.BuildParams{
+			Rule:   android.Touch,
+			Output: s.allowedApexDepsInfoCheckResult,
+		})
+	} else {
+		allowedDeps := allowedDepsSource.Path()
+
+		ctx.Build(pctx, android.BuildParams{
+			Rule:   generateApexDepsInfoFilesRule,
+			Inputs: append(updatableFlatLists, allowedDeps),
+			Output: newAllowedDeps,
+		})
+
+		ctx.Build(pctx, android.BuildParams{
+			Rule:   diffAllowedApexDepsInfoRule,
+			Input:  newAllowedDeps,
+			Output: s.allowedApexDepsInfoCheckResult,
+			Args: map[string]string{
+				"allowed_deps":     allowedDeps.String(),
+				"new_allowed_deps": newAllowedDeps.String(),
+			},
+		})
+	}
 
 	ctx.Phony("apex-allowed-deps-check", s.allowedApexDepsInfoCheckResult)
 }