feat(iferr): add `-message` support (#89)

* feat(iferr): add *-message* support

* generate docs

doc/gopher.nvim.txt

···
       -- default tags to add to struct fields
       default_tag = "json",
     },
+    iferr = {
+      -- choose a custom error message
+      ---@type string|nil
+      message = nil,
+    },
   }
 <
 Class ~

lua/gopher/config.lua

···
     -- default tags to add to struct fields
     default_tag = "json",
   },
+  iferr = {
+    -- choose a custom error message
+    ---@type string|nil
+    message = nil,
+  },
 }
 --minidoc_afterlines_end
 

lua/gopher/iferr.lua

···
   local pos = vim.fn.getcurpos()[2]
   local fpath = vim.fn.expand "%"
 
-  local rs = r.sync({ c.commands.iferr, "-pos", curb }, {
+  local cmd = { c.commands.iferr, "-pos", curb }
+  if c.iferr.message ~= nil and type(c.iferr.message) == "string" then
+    table.insert(cmd, "-message")
+    table.insert(cmd, c.iferr.message)
+  end
+
+  local rs = r.sync(cmd, {
     stdin = u.readfile_joined(fpath),
   })
 

spec/fixtures/iferr/message_input.go

···
+package main
+
+func getErr() error { return nil }
+
+func test() error {
+	err := getErr()
+}

spec/fixtures/iferr/message_output.go

···
+package main
+
+func getErr() error { return nil }
+
+func test() error {
+	err := getErr()
+	if err != nil {
+		return fmt.Errorf("failed to %w", err)
+	}
+}

spec/integration/iferr_test.lua

···
   t.eq(t.readfile(tmp), fixtures.output)
 end
 
+T["iferr"]["works with custom message"] = function()
+  local tmp = t.tmpfile()
+  local fixtures = t.get_fixtures "iferr/message"
+  t.writefile(tmp, fixtures.input)
+
+  child.lua [[ require("gopher").setup { iferr = { message = 'fmt.Errorf("failed to %w", err)' } } ]]
+  child.cmd("silent edit " .. tmp)
+  child.fn.setpos(".", { child.fn.bufnr "%", 6, 2, 0 })
+  child.cmd "GoIfErr"
+  child.cmd "write"
+
+  t.eq(t.readfile(tmp), fixtures.output)
+end
+
 return T