feat(diagnostic): add "code" to the diagnostic structure (#17510)

runtime/doc/diagnostic.txt

@@ -39,16 +39,18 @@ modify the diagnostics for a buffer (e.g. |vim.diagnostic.set()|) then it
 requires a namespace.
 
 							*diagnostic-structure*
-A diagnostic is a Lua table with the following keys:
+A diagnostic is a Lua table with the following keys. Required keys are
+indicated with (*):
 
 	bufnr: Buffer number
-	lnum: The starting line of the diagnostic
+	lnum(*): The starting line of the diagnostic
 	end_lnum: The final line of the diagnostic
-	col: The starting column of the diagnostic
+	col(*): The starting column of the diagnostic
 	end_col: The final column of the diagnostic
 	severity: The severity of the diagnostic |vim.diagnostic.severity|
-	message: The diagnostic text
+	message(*): The diagnostic text
 	source: The source of the diagnostic
+	code: The diagnostic code
 	user_data: Arbitrary data plugins or users can add
 
 Diagnostics use the same indexing as the rest of the Nvim API (i.e. 0-based

runtime/lua/vim/lsp/diagnostic.lua

@@ -104,8 +104,10 @@ local function diagnostic_lsp_to_vim(diagnostics, bufnr, client_id)
       severity = severity_lsp_to_vim(diagnostic.severity),
       message = diagnostic.message,
       source = diagnostic.source,
+      code = diagnostic.code,
       user_data = {
         lsp = {
+          -- usage of user_data.lsp.code is deprecated in favor of the top-level code field
           code = diagnostic.code,
           codeDescription = diagnostic.codeDescription,
           tags = diagnostic.tags,
@@ -120,7 +122,8 @@ end
 ---@private
 local function diagnostic_vim_to_lsp(diagnostics)
   return vim.tbl_map(function(diagnostic)
-    return vim.tbl_extend("error", {
+    return vim.tbl_extend("keep", {
+      -- "keep" the below fields over any duplicate fields in diagnostic.user_data.lsp
       range = {
         start = {
           line = diagnostic.lnum,
@@ -134,6 +137,7 @@ local function diagnostic_vim_to_lsp(diagnostics)
       severity = severity_vim_to_lsp(diagnostic.severity),
       message = diagnostic.message,
       source = diagnostic.source,
+      code = diagnostic.code,
     }, diagnostic.user_data and (diagnostic.user_data.lsp or {}) or {})
   end, diagnostics)
 end

test/functional/plugin/lsp/diagnostic_spec.lua

@@ -110,6 +110,7 @@ describe('vim.lsp.diagnostic', function()
         }
       ]]
       eq({code = 42, tags = {"foo", "bar"}, data = "Hello world"}, result[1].user_data.lsp)
+      eq(42, result[1].code)
       eq(42, result[2].code)
       eq({"foo", "bar"}, result[2].tags)
       eq("Hello world", result[2].data)