4 files changed, 67 insertions, 3 deletions
diff --git a/test/functional/api/compatibility_spec.lua b/test/functional/api/compatibility_spec.lua
new file mode 100644
index 0000000000..e0fc625b46
--- /dev/null
+++ b/test/functional/api/compatibility_spec.lua
@@ -0,0 +1,65 @@
+
+local helpers = require('test.functional.helpers')(after_each)
+local lfs = require('lfs')
+local mpack = require('mpack')
+local clear, eq, neq = helpers.clear, helpers.eq, helpers.neq
+
+local read_mpack_file = function(fname)
+  local fd = io.open(fname, 'rb')
+  local data = fd:read('*a')
+  fd:close()
+  local unpack = mpack.Unpacker()
+  return unpack(data)
+end
+
+-- ignore metadata in API function spec
+local remove_function_metadata = function(fspec)
+  fspec['can_fail'] = nil
+  fspec['async'] = nil
+  fspec['method'] = nil
+  fspec['since'] = nil
+  fspec['deprecated_since'] = nil
+  fspec['receives_channel_id'] = nil
+  for idx,_  in ipairs(fspec['parameters']) do
+    fspec['parameters'][idx][2] = ''
+  end
+end
+
+clear()
+local api_level = helpers.call('api_info')['api_level']
+
+describe('api compatibility', function()
+  before_each(clear)
+
+  it("version metadata is sane", function()
+    local info = helpers.call('api_info')
+    local current = info['api_level']['current']
+    local compatibility = info['api_level']['compatibility']
+    neq(current, nil)
+    neq(compatibility, nil)
+    assert(current >= compatibility)
+  end)
+
+  for ver = api_level['compatibility'], api_level['current'] do
+    local path = 'test/functional/fixtures/api-info/' .. tostring(ver) .. '.mpack'
+    it('are backwards compatible with api level '..ver, function()
+      if lfs.attributes(path,"mode") ~= "file" then
+        pending("No fixture found, skipping test")
+        return
+      end
+
+      local old_api = read_mpack_file(path)
+      local api = helpers.call('api_info')
+
+      for _, fspec in ipairs(old_api['functions']) do
+        remove_function_metadata(fspec)
+        for _, fspec_new in ipairs(api['functions']) do
+          if fspec['name'] == fspec_new['name'] then
+            remove_function_metadata(fspec_new)
+            eq(fspec, fspec_new)
+          end
+        end
+      end
+    end)
+  end
+end)
diff --git a/test/functional/eval/api_functions_spec.lua b/test/functional/eval/api_functions_spec.lua
index 2ef67e7808..5345c9782d 100644
--- a/test/functional/eval/api_functions_spec.lua
+++ b/test/functional/eval/api_functions_spec.lua
@@ -106,7 +106,7 @@ describe('api functions', function()
 
   it('have metadata accessible with api_info()', function()
     local api_keys = eval("sort(keys(api_info()))")
-    eq({'error_types', 'functions', 'types'}, api_keys)
+    eq({'api_level', 'error_types', 'functions', 'types'}, api_keys)
   end)
 
   it('are highlighted by vim.vim syntax file', function()
@@ -144,5 +144,4 @@ describe('api functions', function()
     ]])
     screen:detach()
   end)
-
 end)
diff --git a/test/functional/eval/msgpack_functions_spec.lua b/test/functional/eval/msgpack_functions_spec.lua
index 5b87b05652..ae7e1b5609 100644
--- a/test/functional/eval/msgpack_functions_spec.lua
+++ b/test/functional/eval/msgpack_functions_spec.lua
@@ -460,7 +460,7 @@ describe('msgpackparse() function', function()
     eval(cmd)
     eval(cmd)  -- do it again (try to force segfault)
     local api_info = eval(cmd)  -- do it again
-    eq({'error_types', 'functions', 'types'}, api_info)
+    eq({'api_level', 'error_types', 'functions', 'types'}, api_info)
   end)
 
   it('fails when called with no arguments', function()
diff --git a/test/functional/fixtures/api-info/0.mpack b/test/functional/fixtures/api-info/0.mpack
new file mode 100644
index 0000000000..75b236a3c1
--- /dev/null
+++ b/test/functional/fixtures/api-info/0.mpack