[Go] Generate imports with fixed order (#5340)

* use fixed order for golang imports

* grumble

include/flatbuffers/idl.h

@@ -231,6 +231,15 @@ struct Namespace {
   size_t from_table;  // Part of the namespace corresponds to a message/table.
 };
 
+inline bool operator<(const Namespace &a, const Namespace &b) {
+  size_t min_size = std::min(a.components.size(), b.components.size());
+  for (size_t i = 0; i < min_size; ++i) {
+    if (a.components[i] != b.components[i])
+      return a.components[i] < b.components[i];
+  }
+  return a.components.size() < b.components.size();
+}
+
 // Base class for all definition types (fields, structs_, enums_).
 struct Definition {
   Definition()

src/idl_gen_go.cpp

@@ -113,7 +113,13 @@ class GoGenerator : public BaseGenerator {
  private:
   Namespace go_namespace_;
   Namespace *cur_name_space_;
-  std::set<const Namespace*> tracked_imported_namespaces_;
+
+  struct NamespacePtrLess {
+    bool operator()(const Namespace *a, const Namespace *b) const {
+      return *a < *b;
+    }
+  };
+  std::set<const Namespace *, NamespacePtrLess> tracked_imported_namespaces_;
 
   // Most field accessors need to retrieve and test the field offset first,
   // this is the prefix code for that.