fix(lsp): avoid reusing diagnostics from different servers in actions (#30002)

Problem: When preparing the parameters for a code actions LSP request,
the code set `context.diagnostics` when processing the first LSP client,
and then reused those `context.diagnostics` for subsequent LSP clients.

This meant that the second and next LSP clients got diagnostics that
did not originate from them, and they did not get the diagnostics that
they sent.

Solution: Avoid setting `context.diagnostics` (which is referenced by
all clients). Instead, set `params.context.diagnostics` directly, which
is specific to a single client.

Fixes #30001
Caused by #29501

1 files changed, 10 insertions, 6 deletions

diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index a512d48a06..d7463d74f8 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -897,19 +897,23 @@ function M.code_action(opts)
     else
       params = util.make_range_params(win, client.offset_encoding)
     end
-    if not context.diagnostics then
+    if context.diagnostics then
+      params.context = context
+    else
       local ns_push = vim.lsp.diagnostic.get_namespace(client.id, false)
       local ns_pull = vim.lsp.diagnostic.get_namespace(client.id, true)
       local diagnostics = {}
       local lnum = api.nvim_win_get_cursor(0)[1] - 1
       vim.list_extend(diagnostics, vim.diagnostic.get(bufnr, { namespace = ns_pull, lnum = lnum }))
       vim.list_extend(diagnostics, vim.diagnostic.get(bufnr, { namespace = ns_push, lnum = lnum }))
-      ---@diagnostic disable-next-line: no-unknown
-      context.diagnostics = vim.tbl_map(function(d)
-        return d.user_data.lsp
-      end, diagnostics)
+      params.context = vim.tbl_extend('force', context, {
+        ---@diagnostic disable-next-line: no-unknown
+        diagnostics = vim.tbl_map(function(d)
+          return d.user_data.lsp
+        end, diagnostics),
+      })
     end
-    params.context = context
+
     client.request(ms.textDocument_codeAction, params, on_result, bufnr)
   end
 end