feat: refresh jdtls build path on new java files

A java file created in-editor isn't on jdtls' build path until the
project configuration is refreshed, so go-to-definition returns nothing
on it (find-references still works off the search index). Mark buffers
created in-editor (BufNewFile, or unsaved file absent on disk when setup
runs lazily) and fire java/projectConfigurationUpdate on their first
write. Controlled by the update_config_on_new_file option (default on);
update_project_config gains bufnr and silent params.

Author: artur-shaik

README.md

@@ -63,6 +63,7 @@ require("jc").setup({
   autoformat_on_save = false,  -- format java buffers on save
   debug_backend = nil,         -- "dap" | "vimspector" | nil (auto-detect)
   basedir = nil,               -- data dir, default ~/.local/share/jc.nvim
+  update_config_on_new_file = true, -- refresh jdtls build path on new java files
   on_attach = nil,             -- function(client, bufnr) extra hook
 })
 ```
@@ -71,6 +72,13 @@ The legacy `g:jc_default_mappings`, `g:jc_autoformat_on_save`,
 `g:jc_debug_backend` and `g:jc_basedir` variables still work as a
 fallback when the corresponding option is not passed to `setup`.
 
+A java file created in-editor isn't on jdtls' build path until the project
+configuration is refreshed, so go-to-definition returns nothing on it (while
+find-references still works off the search index). With
+`update_config_on_new_file` (default `true`), jc.nvim detects such files and
+fires `:JCutilUpdateConfig` for them on first write automatically. Set it to
+`false` to refresh manually.
+
 ## What it adds over plain nvim-jdtls
 
 | Feature | nvim-jdtls | jc.nvim |

doc/jc.txt

@@ -58,6 +58,7 @@ Call `setup` (or use the `opts` table of lazy.nvim): >lua
     autoformat_on_save = false,  -- format java buffers on save
     debug_backend = nil,         -- "dap" | "vimspector" | nil = auto
     basedir = nil,               -- data dir, ~/.local/share/jc.nvim
+    update_config_on_new_file = true, -- refresh build path on new java files
     on_attach = nil,             -- function(client, bufnr) extra hook
   })
 <

lua/jc.lua

@@ -5,6 +5,9 @@ local user_on_attach = function(_, _) end
 
 local default_config = {
   keys_prefix = "<leader>j",
+  -- refresh the jdtls build path when a java file is created in-editor, so
+  -- go-to-definition resolves on it without a manual :JCutilUpdateConfig
+  update_config_on_new_file = true,
 }
 
 -- setup(opts) is the single configuration entry point; these opts are
@@ -56,6 +59,46 @@ function M.setup(args)
     end,
   })
 
+  -- Newly created java files aren't on jdtls' build path until the project
+  -- configuration is refreshed, so go-to-definition returns nothing on them
+  -- (find-references still works off the search index). Mark files created
+  -- in-editor (BufNewFile = path absent on disk) and fire a
+  -- projectConfigurationUpdate on their first write so gd resolves.
+  if M.config.update_config_on_new_file ~= false then
+    vim.api.nvim_create_autocmd("BufNewFile", {
+      group = group,
+      pattern = "*.java",
+      callback = function(a)
+        vim.b[a.buf].jc_new_java_file = true
+      end,
+    })
+    -- setup may run lazily on FileType, after BufNewFile already fired for the
+    -- buffer that triggered loading; mark it now if it's an unsaved new file
+    local cur = vim.api.nvim_get_current_buf()
+    if vim.bo[cur].filetype == "java" then
+      local name = vim.api.nvim_buf_get_name(cur)
+      if name ~= "" and vim.fn.filereadable(name) == 0 then
+        vim.b[cur].jc_new_java_file = true
+      end
+    end
+    vim.api.nvim_create_autocmd("BufWritePost", {
+      group = group,
+      pattern = "*.java",
+      callback = function(a)
+        if not vim.b[a.buf].jc_new_java_file then
+          return
+        end
+        vim.b[a.buf].jc_new_java_file = nil
+        -- defer so jdtls processes didSave before we refresh the build path
+        vim.defer_fn(function()
+          if vim.api.nvim_buf_is_valid(a.buf) then
+            require("jc.jdtls").update_project_config(a.buf, { silent = true })
+          end
+        end, 200)
+      end,
+    })
+  end
+
   -- jdtls may already be attached when setup runs (lazy-loaded plugin,
   -- session restore) — hook into the existing clients too
   for _, client in ipairs(vim.lsp.get_clients({ name = "jdtls" })) do

lua/jc/jdtls.lua

@@ -261,14 +261,20 @@ end
 -- jdt.ls declares java/projectConfigurationUpdate as a JsonNotification:
 -- there is never a response, so send a notification (nvim-jdtls sends a
 -- request and its success therefore looks like "nothing happened")
-function M.update_project_config()
+function M.update_project_config(bufnr, opts)
+  bufnr = bufnr or 0
+  opts = opts or {}
   local client = lsp.get_jdtls_client()
   if not client then
-    vim.notify("jc: no jdtls client attached", vim.log.levels.ERROR)
+    if not opts.silent then
+      vim.notify("jc: no jdtls client attached", vim.log.levels.ERROR)
+    end
     return
   end
-  client:notify("java/projectConfigurationUpdate", { uri = vim.uri_from_bufnr(0) })
-  vim.notify("jc: project configuration update requested", vim.log.levels.INFO)
+  client:notify("java/projectConfigurationUpdate", { uri = vim.uri_from_bufnr(bufnr) })
+  if not opts.silent then
+    vim.notify("jc: project configuration update requested", vim.log.levels.INFO)
+  end
 end
 
 local function data_dir_from_args(args)