moduledeps: Module.Equals

Compares two modules for deep equality. This is primarily provided to
enable easy testing of code that constructs module tree structures.

moduledeps/module.go

@@ -133,3 +133,64 @@ func (m *Module) AllPluginRequirements() discovery.PluginRequirements {
 	})
 	return ret
 }
+
+// Equal returns true if the receiver is the root of an identical tree
+// to the other given Module. This is a deep comparison that considers
+// the equality of all downstream modules too.
+//
+// The children are considered to be ordered, so callers may wish to use
+// SortDescendents first to normalize the order of the slices of child nodes.
+//
+// The implementation of this function is not optimized since it is provided
+// primarily for use in tests.
+func (m *Module) Equal(other *Module) bool {
+	// take care of nils first
+	if m == nil && other == nil {
+		return true
+	} else if (m == nil && other != nil) || (m != nil && other == nil) {
+		return false
+	}
+
+	if m.Name != other.Name {
+		return false
+	}
+
+	if len(m.Providers) != len(other.Providers) {
+		return false
+	}
+	if len(m.Children) != len(other.Children) {
+		return false
+	}
+
+	// Can't use reflect.DeepEqual on this provider structure because
+	// the nested VersionSet objects contain function pointers that
+	// never compare as equal. So we'll need to walk it the long way.
+	for inst, dep := range m.Providers {
+		if _, exists := other.Providers[inst]; !exists {
+			return false
+		}
+
+		if dep.Reason != other.Providers[inst].Reason {
+			return false
+		}
+
+		// VersionSets are not too easy to compare robustly, so
+		// we'll just use their string representations as a proxy
+		// for now.
+		if dep.Versions.String() != other.Providers[inst].Versions.String() {
+			return false
+		}
+	}
+
+	// Above we already checked that we have the same number of children
+	// in each module, so now we just need to check that they are
+	// recursively equal.
+	for i := range m.Children {
+		if !m.Children[i].Equal(other.Children[i]) {
+			return false
+		}
+	}
+
+	// If we fall out here then they are equal
+	return true
+}