fix: Debian packages with tar.gz data file (#99)

When a Debian package has a data file that's already compressed with gz
and named data.tar.gz it fails with Error in genrule: rule 'data' has
file 'data.tar.gz' as both an input and an output.

See issue #98

apt/private/deb_import.bzl

@@ -3,14 +3,45 @@
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 # BUILD.bazel template
-_DEB_IMPORT_BUILD_TMPL = """
-# TODO: https://github.com/bazel-contrib/rules_oci/pull/523
-_RECOMPRESS_CMD = "$(ZSTD_BIN) -f --decompress $< --stdout | $(ZSTD_BIN) - --format=gzip >$@"
+_DEB_IMPORT_BUILD_TMPL = '''
 genrule(
     name = "data",
-    srcs = glob(["data.tar.*"]),
-    outs = ["data.tar.gz"],
-    cmd = _RECOMPRESS_CMD,
+    srcs = glob(["data.tar*"]),
+    outs = ["layer.tar.gz"],
+    cmd = """
+    # Per the dpkg-dev man page:
+    # https://manpages.debian.org/bookworm/dpkg-dev/deb.5.en.html
+    #
+    # Debian data.tar files can be:
+    #  - .tar uncompressed, supported since dpkg 1.10.24
+    #  - .tar compressed with
+    #    *  gzip: .gz
+    #    * bzip2: .bz2, supported since dpkg 1.10.24
+    #    *  lzma: .lzma, supported since dpkg 1.13.25
+    #    *    xz: .xz, supported since dpkg 1.15.6
+    #    *  zstd: .zst, supported since dpkg 1.21.18
+    #
+    # ZSTD_BIN can decompress all formats except bzip2
+    #
+    # The OCI image spec supports .tar and .tar compressed with gzip or zstd.
+    # Bazel needs the output filename to be fixed in advanced so we settle for
+    # gzip compression.
+
+    data_file="$$(basename $<)"
+
+    if [[ "$$data_file" == "data.tar.bz2" ]]; then
+      # TODO: support bz2
+      echo "ERROR: unsupported compression: bz2"
+      exit 1
+    elif [[ "$$data_file" == "data.tar.gz" ]]; then
+      mv $< $@
+    elif [[ "$$data_file" == "data.tar" ]]; then
+      $(ZSTD_BIN) --compress --format=gzip $< >$@
+    else
+      $(ZSTD_BIN) --force --decompress --stdout $< |
+      $(ZSTD_BIN) --compress --format=gzip - >$@
+    fi
+    """,
     toolchains = ["@zstd_toolchains//:resolved_toolchain"],
     visibility = ["//visibility:public"],
 )
@@ -20,7 +51,7 @@ filegroup(
     srcs = glob(["control.tar.*"]),
     visibility = ["//visibility:public"],
 )
-"""
+'''
 
 def deb_import(**kwargs):
     http_archive(