__package_dpkg: improve local deb info retrieval

this type forces you to put a correct object id name in order to get
idempotency. dpkg-deb command, when available, makes that work for you,
facilitating the usage of this type

cdist/conf/type/__package_dpkg/gencode-remote

@@ -28,7 +28,12 @@
 # do any checks or --force'ing.
 #
 state=$( cat "$__object/parameter/state" )
-package=$( basename "$__object_id" )
+package_path=$( cat "$__object/parameter/source" )
+if command -v dpkg-deb 2>&1 > /dev/null; then
+    package="$(dpkg-deb --show --showformat='${binary:Package}_${Version}_${Architecture}.deb\n' ${package_path})"
+else
+    package="$( basename "$__object_id" )"
+fi
 state_is="$(cat "$__object/explorer/pkg_state")"
 state_should=""
 
@@ -37,7 +42,7 @@ state_should=""
 
 case "$state" in
     present)
-        echo "dpkg --install /var/cache/apt/archives/$__object_id"
+        echo "dpkg --install /var/cache/apt/archives/${package}"
         echo "installed" >> "$__messages_out"
         ;;
     absent)

cdist/conf/type/__package_dpkg/man.rst

@@ -11,7 +11,8 @@ DESCRIPTION
 This type is used on Debian and variants (like Ubuntu) to
 install packages that are provided locally as \*.deb files.
 
-The object given to this type must be the name of the deb package.
+If the command `dpkg-deb(1)` is not available locally,
+the object given to this type must be the name of the deb package.
 The filename of the deb package has to follow Debian naming conventions, i.e.
 `${binary:Package}_${Version}_${Architecture}.deb` (see `dpkg-query(1)` for
 details).

cdist/conf/type/__package_dpkg/manifest

@@ -27,14 +27,20 @@
 
 state=$( cat "$__object/parameter/state" )
 package_path=$( cat "$__object/parameter/source" )
-package=$( basename "$__object_id" )
+if command -v dpkg-deb 2>&1 > /dev/null; then
+    package="$(dpkg-deb --show --showformat='${binary:Package}_${Version}_${Architecture}.deb\n' ${package_path})"
+else
+    package="$( basename "$__object_id" )"
+fi
 state_is="$(cat "$__object/explorer/pkg_state")"
 state_should=""
 
 [ "$state" = "absent" ] || state_should="$package"
-[ "$state_is" = "$state_should" ] && exit 0
-
-__file "/var/cache/apt/archives/$package" \
-    --source "$package_path" \
-    --state  "$state"
 
+if [ "$state_is" = "$state_should" ]; then
+    exit 0
+else
+    __file "/var/cache/apt/archives/$package" \
+        --source "$package_path" \
+        --state  "$state"
+fi