Description of problem:

The dnf man page says:

       dnf [options] swap <remove-spec> <install-spec>
          Remove  spec and install spec in one transaction. Each <spec> can be
          either a <package-spec>, which specifies a package  directly,  or  a
          @<group-spec>, which specifies an (environment) group which contains
          it. Automatic conflict solving is provided in DNF  by  the  --allow‐
          erasing  option  that provides the functionality of the swap command
          automatically.

It is not clear if <package-spec> is just N(E(V(R(A)))) or if it can also be local rpm file. The man page also says

       For an explanation of <package-spec>,  <package-file-spec>  and
       <package-name-spec> see Specifying Packages.

and

  SPECIFYING PACKAGES
       Many  commands  take  a <package-spec> parameter that selects a package
       for the operation. The <package-spec> argument is matched against pack‐
       age NEVRAs, provides and file provides.

which would suggest local rpm cannot be used as <package-spec> ... but then

       dnf [options] install <spec>...
              Makes  sure  that  the given packages and their dependencies are
              installed  on  the  system.  Each  <spec>  can   be   either   a
              <package-spec>,  or  a  @<module-spec>, or a @<group-spec>.  See
              Install Examples.

and

   Install Examples
       dnf install tito
              Install the tito package (tito is the package name).

       dnf install ~/Downloads/tito-0.6.2-1.fc22.noarch.rpm
              Install a local rpm file tito-0.6.2-1.fc22.noarch.rpm  from  the
              ~/Downloads/ directory.

show that ~/Downloads/tito-0.6.2-1.fc22.noarch.rpm is accepted by install's <package-spec>, leading to conclusion that dnf swap should accept local rpm file as well.

However, attempt to use local rpm file for swap's <install-spec> fails.

Version-Release number of selected component (if applicable):

dnf-4.9.0-1.fc35.noarch

How reproducible:

Deterministic.

Steps to Reproduce:
1. Check that swap in general works:

# dnf swap tar apr
Dependencies resolved.
================================================================================
 Package      Architecture    Version                  Repository          Size
================================================================================
Installing:
 apr          x86_64          1.7.0-14.fc35            fedora             123 k
Removing:
 tar          x86_64          2:1.34-2.fc35            @anaconda          3.0 M

Transaction Summary
================================================================================
Install  1 Package
Remove   1 Package

Total size: 123 k
Is this ok [y/N]: n
Operation aborted.

2. Download the package as local rpm:

# dnf install --downloadonly -y apr
[...]

DNF will only download packages for the transaction.
Downloading Packages:
apr-1.7.0-14.fc35.x86_64.rpm                    2.1 MB/s | 123 kB     00:00    
--------------------------------------------------------------------------------
Total                                           818 kB/s | 123 kB     00:00     
Complete!
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.

3. find /var/cache/dnf -name 'apr*.rpm'
/var/cache/dnf/fedora-37d3cae0527b6391/packages/apr-1.7.0-14.fc35.x86_64.rpm

4. Check that installing local rpm in general works:

# dnf install /var/cache/dnf/fedora-37d3cae0527b6391/packages/apr-1.7.0-14.fc35.x86_64.rpm
[...]
Dependencies resolved.
================================================================================
 Package     Architecture   Version                  Repository            Size
================================================================================
Installing:
 apr         x86_64         1.7.0-14.fc35            @commandline         123 k

Transaction Summary
================================================================================
Install  1 Package

Total size: 123 k
Installed size: 289 k
Is this ok [y/N]: n
Operation aborted.

5. Now try to swap with local rpm file:

# dnf swap tar /var/cache/dnf/fedora-37d3cae0527b6391/packages/apr-1.7.0-14.fc35.x86_64.rpm

Actual results:

Error: Cannot add local packages, because transaction job already exists

Expected results:

Dependencies resolved.
================================================================================
 Package      Architecture    Version                  Repository          Size
================================================================================
Installing:
 apr          x86_64          1.7.0-14.fc35            @commandline       123 k
Removing:
 tar          x86_64          2:1.34-2.fc35            @anaconda          3.0 M

Transaction Summary
================================================================================
Install  1 Package
Remove   1 Package

Total size: 123 k
Is this ok [y/N]: n
Operation aborted.

Additional info:

Of course the real use-case is to use something like

# dnf swap 'centos-*' ./redhat-release-8.5-0.8.el8.x86_64.rpm

on CentOS Linux 8 but the above reproducer shows that swap acts weird on Fedora as well.