scripts: Honor the -e flag for scripts

This is required for glibc-all-langpacks at least:
https://bugzilla.redhat.com/show_bug.cgi?id=1367585

Otherwise, its usage is...extraordinarily rare. In fact looking at a snapshot of
`rpm-specs-20170518.tar.xz` from Fedora, the only other use is in
`postfix.spec`, and it appears bogus (the value is already expanded at build
time).

But the glibc case is special, as the value of `install_langs` is indeed
potentially dynamic per system.

Closes: #873
Approved by: jlebon

src/libpriv/rpmostree-scripts.c

@@ -28,6 +28,13 @@
 
 #include "rpmostree-scripts.h"
 
+/* This bit is currently private in librpm */
+enum rpmscriptFlags_e {
+  RPMSCRIPT_FLAG_NONE		= 0,
+  RPMSCRIPT_FLAG_EXPAND	= (1 << 0), /* macro expansion */
+  RPMSCRIPT_FLAG_QFORMAT	= (1 << 1), /* header queryformat expansion */
+};
+
 typedef struct {
     const char *desc;
     rpmsenseFlags sense;
@@ -224,8 +231,12 @@ impl_run_rpm_script (const KnownRpmScriptKind *rpmscript,
                      GCancellable  *cancellable,
                      GError       **error)
 {
+  g_autofree char *script_owned = NULL;
   const char *script = headerGetString (hdr, rpmscript->tag);
   g_assert (script);
+  const rpmFlags flags = headerGetNumber (hdr, rpmscript->flagtag);
+  if (flags & RPMSCRIPT_FLAG_EXPAND)
+    script = script_owned = rpmExpand (script, NULL);
 
   struct rpmtd_s td;
   g_autofree char **args = NULL;

tests/common/libtest.sh

@@ -377,7 +377,7 @@ Summary: %{name}
 License: GPLv2+
 EOF
 
-    local build= install= files= pretrans= pre= post= posttrans= post_interp=
+    local build= install= files= pretrans= pre= post= posttrans= post_args=
     while [ $# -ne 0 ]; do
         local section=$1; shift
         local arg=$1; shift
@@ -388,8 +388,8 @@ EOF
             echo "Provides: $arg" >> $spec;;
         conflicts)
             echo "Conflicts: $arg" >> $spec;;
-        post_interp)
+        post_args)
-            post_interp="$arg"; post="$1"; shift;;
+            post_args="$arg";;
         version|release|arch|build|install|files|pretrans|pre|post|posttrans)
             declare $section="$arg";;
         *)
@@ -417,7 +417,7 @@ $pretrans
 ${pre:+%pre}
 $pre
 
-${post:+%post} ${post_interp:+-p ${post_interp}}
+${post:+%post} ${post_args}
 $post
 
 ${posttrans:+%posttrans}

tests/vmcheck/test-layering-scripts.sh

@@ -32,7 +32,8 @@ vm_build_rpm scriptpkg1 \
   pre "groupadd -r scriptpkg1" \
   pretrans "# http://lists.rpm.org/pipermail/rpm-ecosystem/2016-August/000391.html
             echo i should've been ignored && exit 1" \
-  post_interp /usr/bin/python 'open("/usr/lib/rpmostreetestinterp", "w")' \
+  post_args "-p /usr/bin/python" \
+  post 'open("/usr/lib/rpmostreetestinterp", "w")' \
   posttrans "# Firewalld; https://github.com/projectatomic/rpm-ostree/issues/638
              . /etc/os-release || :
              # See https://github.com/projectatomic/rpm-ostree/pull/647
@@ -63,6 +64,19 @@ echo "ok group scriptpkg1 active"
 vm_has_files "/usr/lib/rpmostreetestinterp"
 echo "ok interp"
 
+vm_build_rpm scriptpkg2 \
+             post_args "-e" \
+             post 'echo %%{_prefix} > /usr/lib/prefixtest.txt'
+vm_build_rpm scriptpkg3 \
+             post 'echo %%{_prefix} > /usr/lib/noprefixtest.txt'
+vm_rpmostree pkg-add scriptpkg{2,3}
+vm_rpmostree ex livefs
+vm_cmd cat /usr/lib/noprefixtest.txt > noprefixtest.txt
+assert_file_has_content noprefixtest.txt '%{_prefix}'
+vm_cmd cat /usr/lib/prefixtest.txt > prefixtest.txt
+assert_file_has_content prefixtest.txt "/usr"
+echo "ok script expansion"
+
 # And now, things that should fail
 vm_build_rpm rofiles-violation \
   post "echo should fail >> /usr/share/licenses/glibc/COPYING"