rpmbuild ignores /usr/lib/macros if option --macros=file is used

[Fraser]

Building on Ubuntu 15.10 with RPM version 4.12.0.1+dfsg1-3build2

I expect that specifying a macros file with --macros <filename> should allow me to add or redefine the existing macros.

Instead it seems that only the macros file I specify is read, and the macros in the "official" macros file are no longer able to be evaluated.

# Simple test case: Command fails when any macros file is specified, even an empty one:
fhanson@fhanson-linux:~/$ rpm --macros=/dev/null --eval '%{__spec_install_template}'
%{__spec_install_template}

# expected output:
fhanson@fhanson-linux:~/$ rpm --eval '%{__spec_install_template}'
#!/bin/sh

  RPM_SOURCE_DIR="/ssd/home/fhanson/rpmbuild/SOURCES"
  RPM_BUILD_DIR="/ssd/home/fhanson/rpmbuild/BUILD"
  RPM_OPT_FLAGS="-O2 -g"
  RPM_ARCH="x86_64"
  RPM_OS="linux"
  export RPM_SOURCE_DIR RPM_BUILD_DIR RPM_OPT_FLAGS RPM_ARCH RPM_OS
  RPM_DOC_DIR="%{_docdir}"
  export RPM_DOC_DIR
  RPM_PACKAGE_NAME="%{name}"
  RPM_PACKAGE_VERSION="%{version}"
  RPM_PACKAGE_RELEASE="%{release}"
  export RPM_PACKAGE_NAME RPM_PACKAGE_VERSION RPM_PACKAGE_RELEASE
  LANG=C
  export LANG
  unset CDPATH DISPLAY ||:
  RPM_BUILD_ROOT="/ssd/home/fhanson/rpmbuild/BUILDROOT/%{name}-%{version}-%{release}.x86_64"
  export RPM_BUILD_ROOT

  PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:/usr/lib64/pkgconfig:/usr/share/pkgconfig"
  export PKG_CONFIG_PATH

  exec > /dev/null
  umask 022
  cd "/ssd/home/fhanson/rpmbuild/BUILD"

I attempted to reproduce this on SLES11Sp2 (rpm 4.4.2.3) and could not.
This causes all of my rpm builds to fail that use a macros file, because all stage scripts are created with un-expanded macros.
Instead of my prep stage looking like this:
#!/bin/sh
...stuff

It looks like this:
%{__spec_prep_template}
cd '/ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/BUILD'
rm -rf 'define-0.1'
%{__gzip} -dc '/ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/SOURCES/define-0.1.tar.gz' | %{__tar} -xf -
STATUS=$?
if [ $STATUS -ne 0 ]; then
  exit $STATUS
fi
cd 'define-0.1'

This results in a failed build, because of course %{__spec_prep_template} is not a valid shebang line.

%{__spec_prep_post}fhanson@fhanson-linux:~/git/sustaining/sustaining/src/define (master)$ cat /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/tmp/rpm-tmp.OGXomQ make rpm
Building rpm package version 0.1 ...
mkdir -p build
cp -r rpmbuild build/
rpm --initdb --dbpath /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/rpmdb
tar xzf rpmbuild/SOURCES/define-0.1.tar.gz -C build/rpmbuild/BUILDROOT --strip-components=1
cd build/rpmbuild/; rpmbuild -vv --macros=rpmmacros --define="_topdir /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild" -bb SPECS/define.spec
ufdio: 1 reads, 15439 total bytes in 0.000006 secs
Executing(%prep): %{__spec_prep_cmd} /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/tmp/rpm-tmp.6vTHsV
error: Exec of /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/tmp/rpm-tmp.6vTHsV failed (%prep): No such file or directory
error: Bad exit status from /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/tmp/rpm-tmp.6vTHsV (%prep)

RPM build errors:
    Bad exit status from /ssd/home/fhanson/git/sustaining/sustaining/src/define/build/rpmbuild/tmp/rpm-tmp.6vTHsV (%prep)
Makefile:91: recipe for target 'rpm' failed
make: *** [rpm] Error 1