%{undefinedtag} expands to itself without an error

Description of problem:
There is %{?tag} for expand-only-if-defined.
There is no easy way to do expand-but-error-if-not-defined as "%{undefinedtag}" quietly expands to "%{undefinedtag}".

Version-Release number of selected component (if applicable):
rpm-build-4.7.2-1.fc12.x86_64

How reproducible:
Always.

Steps to Reproduce:
cat >undefinedtag.spec <<EOH
Summary: undefinedtag
Name: undefinedtag
Version: 1
Release: 1%{undefinedtag}
License: GPLv3+
%description
undefinedtag
EOH
rpmbuild -bb undefinedtag.spec
echo $?

Actual results:
Checking for unpackaged file(s): /usr/lib/rpm/check-files /.../BUILDROOT/undefinedtag-1-1%{undefinedtag}.x86_64
0

Expected results:
Error at undefinedtag.spec:4: "undefinedtag" is not defined
1

Yes.

Macros that are undefined are passed through literally. The
original reason was so that section markers like %prep could
be overloaded with identically named macros.

(aside) The two lines that need to be added to
make an undefined macro expansion an error have been in
the code, either under an #ifdef or commented out, since 1998.

There is a %{!?foo:...} ("if not defined") construct and a %error primitive that
can be combined to produce an error msg when a macro is undefined.
But that's hardly "easy".

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rpm-build-4.8.1-5.fc14.x86_64

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