api: api_info()['version']

API level is disconnected from NVIM version. The API metadata holds the
current API level, and the lowest backwards-compatible level supported
by this instance.

Release 0.1.6 is the first release that reports the Nvim version and API
level.

    metadata['version'] = {
      major: 0,
      minor: 1,
      patch: 6,
      api_level: 1,
      api_compatible: 0,
      api_prerelease: false,
    }

The API level may remain unchanged across Nvim releases if the API has
not changed.

When changing the API,
    - set NVIM_API_PRERELEASE to true
    - increment NVIM_API_LEVEL (at most once per Nvim version)
    - adjust NVIM_API_LEVEL_COMPAT if backwards-compatibility was broken

api_level_0.mpack was generated from Nvim 0.1.5 with:
    nvim --api-info

1 files changed, 12 insertions, 0 deletions

diff --git a/src/nvim/version.c b/src/nvim/version.c
index 498afa9656..7ab8c84569 100644
--- a/src/nvim/version.c
+++ b/src/nvim/version.c
@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <limits.h>
 
+#include "nvim/api/private/helpers.h"
 #include "nvim/vim.h"
 #include "nvim/ascii.h"
 #include "nvim/iconv.h"
@@ -2514,6 +2515,17 @@ bool has_vim_patch(int n)
   return false;
 }
 
+Dictionary version_dict(void) {
+  Dictionary d = ARRAY_DICT_INIT;
+  PUT(d, "major", INTEGER_OBJ(NVIM_VERSION_MAJOR));
+  PUT(d, "minor", INTEGER_OBJ(NVIM_VERSION_MINOR));
+  PUT(d, "patch", INTEGER_OBJ(NVIM_VERSION_PATCH));
+  PUT(d, "api_level", INTEGER_OBJ(NVIM_API_LEVEL));
+  PUT(d, "api_compatible", INTEGER_OBJ(NVIM_API_LEVEL_COMPAT));
+  PUT(d, "api_prerelease", BOOLEAN_OBJ(NVIM_API_PRERELEASE));
+  return d;
+}
+
 void ex_version(exarg_T *eap)
 {
   // Ignore a ":version 9.99" command.