Add append/prepend support to pkg-bindist --fedora-dist-tag

2 files changed, 48 insertions, 8 deletions

diff --git a/bpkg/pkg-bindist.cli b/bpkg/pkg-bindist.cli
index 65fbeae..1b86cbe 100644
--- a/bpkg/pkg-bindist.cli
+++ b/bpkg/pkg-bindist.cli
@@ -443,11 +443,13 @@ namespace bpkg
     string --fedora-dist-tag
     {
       "<tag>",
-      "Alternative distribution tag to use in the binary package release. If
-       empty value is specified, then no distribution tag is included. The
-       default is a value that identifies the distribution being used to build
-       the package, for example, \cb{fc35} for Fedora 35 or \cb{el8} for RHEL
-       8."
+      "Alternative or additional distribution tag to use in the binary package
+       release. If the specified value starts/ends with \cb{+} then the value
+       (with \cb{+} removed) is added after/before the default distribution
+       tag. Otherwise it is used as is instead of the default tag. If empty
+       value is specified, then no distribution tag is included. The default
+       is a value that identifies the distribution being used to build the
+       package, for example, \cb{fc35} for Fedora 35 or \cb{el8} for RHEL 8."
     }
 
     string --fedora-packager
diff --git a/bpkg/system-package-manager-fedora.cxx b/bpkg/system-package-manager-fedora.cxx
index e22412c..4034932 100644
--- a/bpkg/system-package-manager-fedora.cxx
+++ b/bpkg/system-package-manager-fedora.cxx
@@ -2459,10 +2459,48 @@ namespace bpkg
 
       if (!dist.empty ())
       {
-        // Insert the leading dot into the distribution tag if missing.
+        bool f (dist.front () == '+');
+        bool b (dist.back () == '+');
+
+        if (f && b) // Note: covers just `+`.
+          fail << "invalid distribution tag '" << dist << "'";
+
+        // If the distribution tag is specified with a leading/trailing '+',
+        // then we query the default tag value and modify it using the
+        // specified suffix/prefix.
         //
-        if (dist.front () != '.')
-          dist.insert (dist.begin (), '.');
+        // Note that we rely on the fact that the dist tag doesn't depend on
+        // the --target option which we also pass to rpmbuild.
+        //
+        if (f || b)
+        {
+          string affix (move (dist));
+          strings expansions (rpm_eval (cstrings (), cstrings {"%{?dist}"}));
+
+          if (expansions.size () != 1)
+            fail << "one line expected as an expansion of macro %{?dist}";
+
+          dist = move (expansions[0]);
+
+          // Normally, the default distribution tag starts with the dot, in
+          // which case we insert the prefix after it. Note, however, that the
+          // tag can potentially be re/un-defined (for example in
+          // ~/.rpmmacros), so we need to also handle the potential absence of
+          // the leading dot inserting the prefix right at the beginning in
+          // this case.
+          //
+          if (f)
+            dist.append (affix, 1, affix.size () - 1);
+          else
+            dist.insert (dist[0] == '.' ? 1 : 0, affix, 0, affix.size () - 1);
+        }
+        else
+        {
+          // Insert the leading dot into the distribution tag if missing.
+          //
+          if (dist.front () != '.')
+            dist.insert (dist.begin (), '.');
+        }
 
         common_opts.push_back ("--define=dist " + dist);
       }