func processFile()

in kinder/hack/orderimports/orderimports.go [87:160]
65 lines of code
18 McCabe index (conditional complexity)

func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error {
	fileSet := token.NewFileSet() // per file FileSet

	var perm fs.FileMode = 0644
	if in == nil {
		f, err := os.Open(filename)
		if err != nil {
			return err
		}
		defer f.Close()
		fi, err := f.Stat()
		if err != nil {
			return err
		}
		in = f
		perm = fi.Mode().Perm()
	}

	src, err := io.ReadAll(in)
	if err != nil {
		return err
	}

	astFile, err := parser.ParseFile(fileSet, filename, src, parserMode)
	if err != nil {
		return err
	}

	sortImports(fileSet, astFile)

	var buf bytes.Buffer
	cfg := printer.Config{Mode: printerMode, Tabwidth: tabWidth}
	err = cfg.Fprint(&buf, fileSet, astFile)
	if err != nil {
		return err
	}
	res := buf.Bytes()

	if !bytes.Equal(src, res) {
		// formatting has changed
		if *list {
			fmt.Fprintln(out, filename)
		}
		if *write {
			// make a temporary backup before overwriting original
			bakname, err := backupFile(filename+".", src, perm)
			if err != nil {
				return err
			}
			err = os.WriteFile(filename, res, perm)
			if err != nil {
				os.Rename(bakname, filename)
				return err
			}
			err = os.Remove(bakname)
			if err != nil {
				return err
			}
		}
		if *doDiff {
			data, err := diffWithReplaceTempFile(src, res, filename)
			if err != nil {
				return fmt.Errorf("computing diff: %s", err)
			}
			fmt.Printf("diff -u %s %s\n", filepath.ToSlash(filename+".orig"), filepath.ToSlash(filename))
			out.Write(data)
		}
	}
	if !*list && !*write && !*doDiff {
		_, err = out.Write(res)
	}

	return err
}