obsolete-1.0.tcl: Allow replaced_by to be set later

Previously, replaced_by needed to be set before the portgroup was
included. Now it can be set, changed, or unset, before or after.

Closes: https://trac.macports.org/ticket/56023

_resources/port1.0/group/obsolete-1.0.tcl

@@ -32,8 +32,8 @@
 #
 # Usage:
 #
-#   replaced_by         name-of-port-that-deprecated-this-port
 #   PortGroup           obsolete 1.0
+#   replaced_by         name-of-port-that-deprecated-this-port
 
 # set a number of reasonable defaults for a port that is only there to
 # inform users that they should uninstall it and install something else
@@ -43,12 +43,32 @@ platforms       darwin
 maintainers     nomaintainer
 supported_archs noarch
 
+proc obsolete.set_descriptions {replaced_by} {
+    if {${replaced_by} eq ""} {
+        description         Obsolete port
+        long_description    This port is obsolete.
+    } else {
+        description         Obsolete port, replaced by ${replaced_by}
+        long_description    This port has been replaced by ${replaced_by}.
+    }
+}
+
+# Handle replaced_by set after portgroup inclusion.
+option_proc replaced_by obsolete.replaced_by_proc
+proc obsolete.replaced_by_proc {option action args} {
+    switch ${action} {
+        set -
+        delete {
+            obsolete.set_descriptions ${args}
+        }
+    }
+}
+
+# Handle replaced_by set before portgroup inclusion.
 if {[info exists replaced_by]} {
-    description     Obsolete port, replaced by ${replaced_by}
-    default long_description "This port has been replaced by ${replaced_by}."
+    obsolete.set_descriptions ${replaced_by}
 } else {
-    description     Obsolete port
-    default long_description "This port is obsolete."
+    obsolete.set_descriptions ""
 }
 
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