A diff from libunistring witch my inlined comments.

--- libunistring.spec	2023-01-24 13:14:10.423026317 +0100
+++ libunistring1.0.spec	2023-01-24 13:14:07.795011951 +0100
@@ -1,11 +1,13 @@
+%bcond_with devel
+

I suppose a disabled devel bcond makes sense if we want people to be able to install the lib but not compile against it. +1

 # This spec file has been automatically updated
-Version:	1.1
-Release: %{?autorelease}%{!?autorelease:1%{?dist}}
-Name: libunistring
-Summary: GNU Unicode string library
+Version:	1.0
+Release: 1%{?dist}

I'd keep using %autorelease here as well, but not a big deal.

+Name: libunistring1.0
+Summary: Compatibility version of GNU Unicode string library

Ack.

Please also add: Conflicts: libunistring < 1.1 (as the libunistring package has overlapping files in that version).

 License: GPLv2+ or LGPLv3+

New packages MUST use SPDX license identifiers, please update both packages while doing so.

 URL: https://www.gnu.org/software/libunistring/
-Source0: https://ftp.gnu.org/gnu/libunistring/%{name}-%{version}.tar.xz
+Source0: https://ftp.gnu.org/gnu/libunistring/libunistring-%{version}.tar.xz

Ack.

 BuildRequires: gcc
 BuildRequires: make
 Provides: bundled(gnulib)

Consider providing deprecated() here as well.

@@ -15,17 +17,23 @@
 (UTF-8, UTF-16, UTF-32), together with functions for character processing
 (names, classifications, properties) and functions for string processing
 (iteration, formatted output, width, word breaks, line breaks, normalization,
-case folding and regular expressions).
+case folding and regular expressions). This version of libunistring package
+contains only the library from the 1.0 version and is provided for compatibility
+with previous versions.

I am not a native speaker but the sentence sounds weird to me, how about:

This package contains the libunistring library version 1.0 and is intended for compatibility reasons only.
Users are advised to update to a newer version of libunistring.

 
+%if %{with devel}
 %package devel
 Summary: GNU Unicode string library - development files
 Requires: %{name}%{?_isa} = %{version}-%{release}
+Conflicts: libunistring-devel
+Provides: deprecated()
 
 %description devel
 Development files for programs using libunistring.
+%endif


Please update the summary and description of the devel package (just in case it will need to be enabled).

 %prep
-%autosetup
+%autosetup -n libunistring-%{version}

Ack.

 %build
 %configure --disable-static --disable-rpath
@@ -41,8 +49,9 @@
 %files
 %license COPYING COPYING.LIB
 %doc AUTHORS NEWS README
-%{_libdir}/%{name}.so.5*
+%{_libdir}/%{name}.so.*

I'd hardcode the old version here, to be safe.

+%if %{with devel}
 %files devel
 %doc HACKING DEPENDENCIES THANKS ChangeLog
 %doc __doc/*
@@ -50,8 +59,11 @@
 %{_libdir}/%{name}.so
 %{_includedir}/unistring
 %{_includedir}/*.h
+%endif
 
 %ldconfig_scriptlets

This could possibly be removed, but no big deal.

 %changelog
-%autochangelog
+* Tue Jan 24 2023 Daiki Ueno <dueno> - 1.0-1
+- Create compat package for libunistring 1.1 ABI bump
+

What about:

- Initial compatibility package with libunistring 1.0


------------------


Note that compatibility packages don't need a formal review, so treat my comments as recommendations/suggestions and feel free to request the repo:

  fedpkg request-repo libunistring1.0 --exception (--no-initial-commit)

Use --no-initial-commit if you want to push the git history of https://src.fedoraproject.org/rpms/libunistring/tree/f37

Thanks Miro, I've incorporated the suggested changes and confirmed it builds in mock. Will request a repo soon.

The package has been built in rawhide.