fix: Output JSON on dry-run

Signed-off-by: Julien Jerphanion <[email protected]>

libmamba/src/api/create.cpp

@@ -4,6 +4,8 @@
 //
 // The full license is in the file LICENSE, distributed with this software.
 
+#include <iostream>
+
 #include "mamba/api/configuration.hpp"
 #include "mamba/api/create.hpp"
 #include "mamba/api/install.hpp"
@@ -29,6 +31,7 @@ namespace mamba
 
         auto& create_specs = config.at("specs").value<std::vector<std::string>>();
         auto& use_explicit = config.at("explicit_install").value<bool>();
+        auto& json_format = config.at("json").get_cli_config<bool>();
 
         auto channel_context = ChannelContext::make_conda_compatible(ctx);
 
@@ -78,6 +81,21 @@ namespace mamba
                 );
             }
         }
+        else
+        {
+            if (create_specs.empty() && json_format)
+            {
+                // Just print the JSON
+                nlohmann::json output;
+                output["actions"]["FETCH"] = nlohmann::json::array();
+                output["actions"]["PREFIX"] = ctx.prefix_params.target_prefix;
+                output["dry_run"] = true;
+                output["prefix"] = ctx.prefix_params.target_prefix;
+                output["success"] = true;
+                std::cout << output.dump(2) << std::endl;
+            }
+            return;
+        }
 
         if (ctx.env_lockfile)
         {