singularity build --oci doesn't support URI targets

[nathanweeks]

Before you report an issue...

• Have you searched for a duplicate report?
• Have you replicated the problem on the latest release?
• Have you checked the latest documentation?
• Are you using an up-to-date system?

Only issues that can be replicated on the latest release, or development branch, of SingularityCE will be investigated and fixed. The open source project does not maintain long-term stable branches or fix bugs in prior versions. If you require LTS support then please see the Sylabs website.

Version of Singularity

What version of Singularity are you using? Run:

$ singularity --version
singularity-ce version 4.2.2-1.el8

Describe the bug

singularity build --oci doesn't support URI targets, unlike singularity shell --oci, singularity pull --oci, or singularity build (without --oci)

To Reproduce

$ singularity build --oci ubuntu.oci.sif docker://docker.io/library/ubuntu
INFO:    Did not find usable system buildkitd daemon. Starting built-in singularity-buildkitd.
WARN[0000] git source cannot be enabled: failed to find git binary: exec: "git": executable file not found in $PATH 
INFO:    singularity-buildkitd: running server on /run/user/1000/singularity-buildkitd/singularity-buildkitd-16888.sock
[+] Building 0.0s (0/0)                                                                                                                                                      
INFO:    Terminating singularity-buildkitd (PID 16910)
FATAL:   while building from dockerfile: resolve : lstat docker:: no such file or directory

Expected behavior

I would expect "ubuntu.oci.sif" to be created, as with with an regular SIF if --oci is omitted:

$ singularity build ubuntu.sif docker://docker.io/library/ubuntu
INFO:    Starting build...
INFO:    Fetching OCI image...
28.4MiB / 28.4MiB [========================================================] 100 %0s
INFO:    Extracting OCI image...
INFO:    Inserting Singularity configuration...
INFO:    Creating SIF file...
INFO:    Build complete: ubuntu.sif

OS / Linux Distribution

Which Linux distribution are you using? Is it up-to-date?

$ cat /etc/os-release
NAME="Rocky Linux"
VERSION="8.10 (Green Obsidian)"
ID="rocky"
ID_LIKE="rhel centos fedora"
VERSION_ID="8.10"
PLATFORM_ID="platform:el8"
PRETTY_NAME="Rocky Linux 8.10 (Green Obsidian)"
ANSI_COLOR="0;32"
LOGO="fedora-logo-icon"
CPE_NAME="cpe:/o:rocky:rocky:8:GA"
HOME_URL="https://rockylinux.org/"
BUG_REPORT_URL="https://bugs.rockylinux.org/"
SUPPORT_END="2029-05-31"
ROCKY_SUPPORT_PRODUCT="Rocky-Linux-8"
ROCKY_SUPPORT_PRODUCT_VERSION="8.10"
REDHAT_SUPPORT_PRODUCT="Rocky Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="8.10"

Installation Method

RPM from EPEL

Additional context