gulp.src base option: preserving nested directories during gulp.dest

Preserving Nested Directory Structure with gulp.src Base Option

In Gulp 4.x, the gulp.src stream attaches a base path to each Vinyl file. When the base option is omitted, Gulp defaults to the glob stem before the first wildcard. gulp.dest writes files by appending file.relative to the destination directory, so the final output hierarchy depends entirely on file.base.

Because gulp.dest overwrites existing files without prompting, developers often rely on an explicit base to ensure that nested source folders are preserved and to avoid accidental data loss during a backup‑restore cycle. However, the exact derivation of base when complex globs (e.g., braces, extglob patterns) are used remains unclear, and there is no documented fallback for restoring stripped top‑level directories after a failed build.

Key uncertainty: how does Gulp determine the base path for files matched by globs that contain nested patterns, and can this behavior be reliably controlled to support automated backup and restoration of the full source tree?

• When a glob includes braces or extglob patterns, does Gulp always use the first leading directory before the first wildcard as the base, or does it consider the entire matched path?
• Can a custom transform stage reliably log file.base and file.relative for every file in a complex multi‑glob pipeline to verify the intended output structure?
• Is there a recommended strategy or configuration to preserve the original folder hierarchy across backup and restoration cycles when the base is implicitly derived?