Add default descriptions to every action

src/actions/action_default_v1.h

@@ -16,6 +16,9 @@
 
 class ActionDefault_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Default fallback action for unmatched URIs"};
+
   ActionDefault_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_health_check_v1.h

@@ -13,6 +13,9 @@
 
 class ActionHealthCheck_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Report the server's health status"};
+
   ActionHealthCheck_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_jsonschema_evaluate_v1.h

@@ -26,6 +26,10 @@
 
 class ActionJSONSchemaEvaluate_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Validate a JSON instance against a schema and return whether it "
+      "is valid plus any errors"};
+
   ActionJSONSchemaEvaluate_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_jsonschema_trace_v1.h

@@ -29,6 +29,10 @@
 
 class ActionJSONSchemaTrace_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Validate a JSON instance against a schema and return detailed "
+      "information about every step of the evaluation process"};
+
   ActionJSONSchemaTrace_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_mcp_v1.h

@@ -14,6 +14,9 @@
 
 class ActionMCP_v1 : public sourcemeta::one::Action, public EnterpriseMCP {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Handle Model Context Protocol JSON-RPC requests"};
+
   ActionMCP_v1(const std::filesystem::path &base,
                const sourcemeta::core::URITemplateRouterView &router,
                const sourcemeta::core::URITemplateRouter::Identifier identifier)
@@ -53,6 +56,9 @@ class ActionMCP_v1 : public sourcemeta::one::Action, public EnterpriseMCP {
 
 class ActionMCP_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Handle Model Context Protocol JSON-RPC requests"};
+
   ActionMCP_v1(const std::filesystem::path &base,
                const sourcemeta::core::URITemplateRouterView &router,
                const sourcemeta::core::URITemplateRouter::Identifier identifier)

src/actions/action_not_found_v1.h

@@ -13,6 +13,9 @@
 
 class ActionNotFound_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Return a 404 Not Found response"};
+
   ActionNotFound_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_schema_search_v1.h

@@ -24,6 +24,9 @@
 
 class ActionSchemaSearch_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Search for schemas by query term"};
+
   ActionSchemaSearch_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_serve_explorer_artifact_v1.h

@@ -21,6 +21,9 @@
 
 class ActionServeExplorerArtifact_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Read a navigation artifact for browsing schemas"};
+
   ActionServeExplorerArtifact_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_serve_schema_artifact_v1.h

@@ -21,6 +21,10 @@
 
 class ActionServeSchemaArtifact_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Look up a precomputed artifact about a specific schema by its "
+      "absolute URI"};
+
   ActionServeSchemaArtifact_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/action_serve_static_v1.h

@@ -15,6 +15,9 @@
 
 class ActionServeStatic_v1 : public sourcemeta::one::Action {
 public:
+  static constexpr std::string_view DESCRIPTION{
+      "Serve a static asset bundled with the server"};
+
   ActionServeStatic_v1(
       const std::filesystem::path &base,
       const sourcemeta::core::URITemplateRouterView &router,

src/actions/dispatch.cc

@@ -45,6 +45,24 @@ static constexpr std::array<ActionConstructFunction,
 
 #undef SOURCEMETA_ONE_MAKE_CONSTRUCTOR_ENTRY
 
+#define SOURCEMETA_ONE_DEFINE_DESCRIPTION(Name, Class) Class::DESCRIPTION,
+
+static constexpr std::array<std::string_view,
+                            sourcemeta::one::ACTION_TYPE_COUNT>
+    DESCRIPTIONS{
+        {SOURCEMETA_ONE_FOR_EACH_ACTION(SOURCEMETA_ONE_DEFINE_DESCRIPTION)}};
+
+#undef SOURCEMETA_ONE_DEFINE_DESCRIPTION
+
+auto sourcemeta::one::ActionDispatcher::description(
+    const sourcemeta::core::URITemplateRouter::Identifier context) noexcept
+    -> std::string_view {
+  if (context >= DESCRIPTIONS.size()) {
+    return {};
+  }
+  return DESCRIPTIONS[context];
+}
+
 sourcemeta::one::ActionDispatcher::ActionDispatcher(
     const std::filesystem::path &base,
     const sourcemeta::core::URITemplateRouterView &router)

src/actions/include/sourcemeta/one/actions.h

@@ -118,6 +118,10 @@ class ActionDispatcher {
              const char *const code, std::string &&identifier,
              std::string &&message) const -> void;
 
+  [[nodiscard]] static auto
+  description(core::URITemplateRouter::Identifier context) noexcept
+      -> std::string_view;
+
 private:
   struct Slot {
     std::unique_ptr<Action> instance;

test/unit/actions/CMakeLists.txt

@@ -1,5 +1,6 @@
 sourcemeta_googletest(NAMESPACE sourcemeta PROJECT one NAME actions
   SOURCES
+    actions_descriptions_test.cc
     actions_mcp_default_test.cc
     actions_schema_directory_test.cc
     actions_uri_to_relative_path_test.cc)

test/unit/actions/actions_descriptions_test.cc

@@ -0,0 +1,94 @@
+#include <gtest/gtest.h>
+
+#include <sourcemeta/core/uritemplate.h>
+
+#include <sourcemeta/one/actions.h>
+
+#include <limits>      // std::numeric_limits
+#include <string_view> // std::string_view
+
+TEST(Actions_description, default_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_DEFAULT_V1),
+            std::string_view{"Default fallback action for unmatched URIs"});
+}
+
+TEST(Actions_description, health_check_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_HEALTH_CHECK_V1),
+            std::string_view{"Report the server's health status"});
+}
+
+TEST(Actions_description, not_found_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_NOT_FOUND_V1),
+            std::string_view{"Return a 404 Not Found response"});
+}
+
+TEST(Actions_description, schema_artifact_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_SCHEMA_ARTIFACT_V1),
+            std::string_view{"Look up a precomputed artifact about a "
+                             "specific schema by its absolute URI"});
+}
+
+TEST(Actions_description, explorer_artifact_v1) {
+  EXPECT_EQ(
+      sourcemeta::one::ActionDispatcher::description(
+          sourcemeta::one::ACTION_TYPE_EXPLORER_ARTIFACT_V1),
+      std::string_view{"Read a navigation artifact for browsing schemas"});
+}
+
+TEST(Actions_description, jsonschema_evaluate_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_JSONSCHEMA_EVALUATE_V1),
+            std::string_view{"Validate a JSON instance against a schema and "
+                             "return whether it is valid plus any errors"});
+}
+
+TEST(Actions_description, jsonschema_trace_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_JSONSCHEMA_TRACE_V1),
+            std::string_view{
+                "Validate a JSON instance against a schema and return "
+                "detailed information about every step of the evaluation "
+                "process"});
+}
+
+TEST(Actions_description, schema_search_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_SCHEMA_SEARCH_V1),
+            std::string_view{"Search for schemas by query term"});
+}
+
+TEST(Actions_description, serve_static_v1) {
+  EXPECT_EQ(sourcemeta::one::ActionDispatcher::description(
+                sourcemeta::one::ACTION_TYPE_SERVE_STATIC_V1),
+            std::string_view{"Serve a static asset bundled with the server"});
+}
+
+TEST(Actions_description, mcp_v1) {
+  EXPECT_EQ(
+      sourcemeta::one::ActionDispatcher::description(
+          sourcemeta::one::ACTION_TYPE_MCP_V1),
+      std::string_view{"Handle Model Context Protocol JSON-RPC requests"});
+}
+
+TEST(Actions_description, every_action_has_a_non_empty_description) {
+  for (sourcemeta::core::URITemplateRouter::Identifier context{0};
+       context < sourcemeta::one::ACTION_TYPE_COUNT; ++context) {
+    EXPECT_FALSE(
+        sourcemeta::one::ActionDispatcher::description(context).empty())
+        << "Action context " << context << " has an empty description";
+  }
+}
+
+TEST(Actions_description, out_of_range_returns_empty) {
+  EXPECT_TRUE(sourcemeta::one::ActionDispatcher::description(
+                  sourcemeta::one::ACTION_TYPE_COUNT)
+                  .empty());
+  EXPECT_TRUE(sourcemeta::one::ActionDispatcher::description(
+                  std::numeric_limits<
+                      sourcemeta::core::URITemplateRouter::Identifier>::max())
+                  .empty());
+}