fix: crash in error handling for function formatters (nvim-lua#554)

lua/conform/formatters/injected.lua

@@ -137,6 +137,11 @@ return {
     -- (defaults to the value from formatters_by_ft)
     lang_to_formatters = {},
   },
+  condition = function(self, ctx)
+    local buf_lang = vim.treesitter.language.get_lang(vim.bo[ctx.buf].filetype)
+    local ok = pcall(vim.treesitter.get_string_parser, "", buf_lang)
+    return ok
+  end,
   format = function(self, ctx, lines, callback)
     local conform = require("conform")
     local errors = require("conform.errors")

lua/conform/runner.lua

@@ -309,13 +309,20 @@ local function run_formatter(bufnr, formatter, config, ctx, input_lines, opts, c
     end
   end)
   if config.format then
+    local err_string_cb = function(err, ...)
+      if err then
+        callback({
+          code = errors.ERROR_CODE.RUNTIME,
+          message = err,
+        }, ...)
+      else
+        callback(nil, ...)
+      end
+    end
     ---@cast config conform.LuaFormatterConfig
-    local ok, err = pcall(config.format, config, ctx, input_lines, callback)
+    local ok, err = pcall(config.format, config, ctx, input_lines, err_string_cb)
     if not ok then
-      callback({
-        code = errors.ERROR_CODE.RUNTIME,
-        message = string.format("Formatter '%s' error: %s", formatter.name, err),
-      })
+      err_string_cb(string.format("Formatter '%s' error: %s", formatter.name, err))
     end
     return
   end