into datetime -f doesn't parse a valid format string #17432
Description
Bug report form
- I have done a basic search of the issue tracker to find any existing issues that are similar.
- I have checked that my version is at least the latest stable release available via my installation method.
Describe the bug
When trying to convert unix epoch with milliseconds using into datetime -f "%s%3f" I get the following error: can't convert bad or unsupported format string to could not parse as datetime using format '%s%3f'. Worth mentioning, that format %s%.3f work fine.
It seems like a bug because using the same format string to format a date works as expected. Here is some output with unexpected behavior
> date now | format date "%s%3f"
1769503677954
> date now | format date "%s%3f" | into datetime -f "%s%3f"
Error: nu::shell::cant_convert
× Can't convert to could not parse as datetime using format '%s%3f'.
╭─[entry #42:1:34]
1 │ date now | format date "%s%3f" | into datetime -f "%s%3f"
· ──────┬──────
· ╰── can't convert premature end of input to could not parse as datetime using format '%s%3f'
╰────
help: you can use `into datetime` without a format string to enable flexible parsing
> '1769503677.954' | into datetime -f "%s%.3f"
27/01/26 08:47:57
How to reproduce
date now | format date "%s%3f" | into datetime -f "%s%3f"
Expected behavior
Get a datetime instead of an error
Configuration
| key | value |
|---|---|
| version | 0.110.0 |
| major | 0 |
| minor | 110 |
| patch | 0 |
| branch | makepkg |
| commit_hash | d40e191 |
| build_os | linux-x86_64 |
| build_target | x86_64-unknown-linux-gnu |
| rust_version | rustc 1.92.0 (ded5c06cf 2025-12-08) (Arch Linux rust 1:1.92.0-1) |
| cargo_version | cargo 1.92.0 (344c4567c 2025-10-21) (Arch Linux rust 1:1.92.0-1) |
| build_time | 2026-01-18 07:22:50 +00:00 |
| build_rust_channel | release |
| allocator | standard |
| features | default, mcp, network, plugin, rustls-tls, sqlite, trash-support |
| installed_plugins | |
| experimental_options | example=false, reorder-cell-paths=true, pipefail=false, enforce-runtime-annotations=false |