engine: Support stack minor versions and bump to "4.1"

This should not be a breaking change, since this provides support
for versions "4", "4.0", and "4.1". The idea is that one can specify
in the stack which version you target, and cloe-engine will make
sure it's at least that recent.

For example, if a stackfile requires "4", everything still works.
If it requires "4.1", it will only work with a cloe-engine of at
least this version, which is as intended.

Bumping a version in the future will require modifying the
CLOE_STACK_VERSION and CLOE_STACK_SUPPORTED_VERSIONS defines
in stack.hpp.

Author: cassava

engine/src/stack.cpp

@@ -137,6 +137,7 @@ Conf default_conf_reader(const std::string& filepath) { return Conf{filepath}; }
 Stack::Stack()
     : Confable()
     , reserved_ids_({"_", "cloe", "sim", "simulation"})
+    , version(CLOE_STACK_VERSION)
     , engine_schema(&engine, "engine configuration")
     , include_schema(&include, include_prototype(), "include configurations")
     , plugins_schema(&plugins, "plugin configuration")
@@ -147,6 +148,7 @@ Stack::Stack(const Stack& other)
     // Constants (1)
     , reserved_ids_(other.reserved_ids_)
     // Configuration (13)
+    , version(other.version)
     , engine(other.engine)
     , server(other.server)
     , include(other.include)
@@ -191,6 +193,7 @@ void swap(Stack& left, Stack& right) {
   swap(left.reserved_ids_, right.reserved_ids_);
 
   // Configuration (13)
+  swap(left.version, right.version);
   swap(left.engine, right.engine);
   swap(left.server, right.server);
   swap(left.include, right.include);
@@ -435,27 +438,29 @@ void Stack::to_json(Json& j) const {
 }
 
 void Stack::from_conf(const Conf& _conf, size_t depth) {
+  static std::vector<std::string> versions CLOE_STACK_SUPPORTED_VERSIONS;
+
   applied_confs_.emplace_back(_conf);
   Conf c = _conf;
 
   // First check the version so the user gets higher-level errors first.
   if (c.has("version")) {
     auto ver = c.get<std::string>("version");
-    if (ver != CLOE_STACK_VERSION) {
+    if (std::find(versions.begin(), versions.end(), ver) == versions.end()) {
       // If we threw a SchemaError, it would look like this:
       //
       //     throw SchemaError{
       //       c,
       //       this->schema().json_schema(),
       //       Json{},
-      //       "require version {}, got {}",
+      //       "require version compatible with {}, got {}",
       //       CLOE_STACK_VERSION,
       //       ver,
       //     };
       //
       // But that would result in a very verbose error message, so we shall
       // throw a more user-friendly error message instead.
-      throw Error{"require version {}, got {}", CLOE_STACK_VERSION, ver}.explanation(R"(
+      throw Error{"require version compatible with {}, got {}", CLOE_STACK_VERSION, ver}.explanation(R"(
             It looks like you are attempting to load a stack file with an
             incompatible version.
 

engine/src/stack.hpp

@@ -45,7 +45,11 @@
 #include "plugin.hpp"  // for Plugin
 
 #ifndef CLOE_STACK_VERSION
-#define CLOE_STACK_VERSION "4"
+#define CLOE_STACK_VERSION "4.1"
+#endif
+
+#ifndef CLOE_STACK_SUPPORTED_VERSIONS
+#define CLOE_STACK_SUPPORTED_VERSIONS {"4", "4.0", "4.1"}
 #endif
 
 #ifndef CLOE_XDG_SUFFIX
@@ -887,6 +891,7 @@ class Stack : public Confable {
   boost::optional<std::string> schema_ref_;
 
  public:  // Configuration (13)
+  std::string version;
   EngineConf engine;
   ServerConf server;
   std::vector<IncludeConf> include;
@@ -1091,7 +1096,9 @@ class Stack : public Confable {
 
     return Struct{
         {"$schema", make_schema(&schema_ref_, "valid URI to schema describing this cloe stack version")},
-        {"version", make_const_str(CLOE_STACK_VERSION, "version of stackfile").require()},
+        {"version", make_schema(&version, "version of stackfile").require().enum_of(
+          CLOE_STACK_SUPPORTED_VERSIONS
+        )},
         {"engine", engine_schema},
         {"include", include_schema},
         {"logging", make_schema(&logging, "logging configuration").extend(true)},

engine/src/stack_test.cpp

@@ -37,7 +37,7 @@ TEST(cloe_stack, serialization_of_empty_stack) {
   Stack s;
 
   fable::assert_from_conf(s, R"({
-    "version": "4"
+    "version": "4.1"
   })");
 
   Json expect = R"({
@@ -110,7 +110,7 @@ TEST(cloe_stack, serialization_of_empty_stack) {
     "simulators": [],
     "triggers": [],
     "vehicles": [],
-    "version": "4"
+    "version": "4.1"
   })"_json;
 
   ASSERT_EQ(s.to_json().dump(2), expect.dump(2));
@@ -120,7 +120,7 @@ TEST(cloe_stack, serialization_with_logging) {
   Stack s;
 
   assert_from_conf(s, R"({
-    "version": "4",
+    "version": "4.1",
     "defaults": {
       "simulators": [
         { "binding": "vtd", "args": { "label_vehicle": "symbol" } }
@@ -205,7 +205,7 @@ TEST(cloe_stack, serialization_with_logging) {
     },
     "triggers": [],
     "vehicles": [],
-    "version": "4"
+    "version": "4.1"
   })"_json;
 
   ASSERT_NO_THROW(Json{s.logging[0]}.dump());