Actually append the xz --list after the container differences, as it simplifies a lot.

diffoscope/comparators/xz.py

@@ -70,9 +70,15 @@ class XzFile(File):
     FALLBACK_FILE_EXTENSION_SUFFIX = {".xz"}
     FALLBACK_FILE_TYPE_HEADER_PREFIX = b"\xfd7zXZ\x00"
 
-    def compare_details(self, other, source=None):
-        return [
-            Difference.from_operation(
+    def compare(self, other, source=None):
+        difference = super().compare(other, source)
+
+        # Append xz --list *after* showing any container differences.
+        if isinstance(other, XzFile):
+            xz_list = Difference.from_operation(
                 XZList, self.path, other.path, source="xz --list"
             )
-        ]
+            if xz_list:
+                difference.add_details([xz_list])
+
+        return difference

tests/comparators/test_containers.py

@@ -31,27 +31,36 @@ from ..utils.tools import (
 gzip1 = load_fixture("containers/a.tar.gz")
 gzip2 = load_fixture("containers/b.tar.gz")
 
+xz1 = load_fixture("containers/a.tar.xz")
+xz2 = load_fixture("containers/b.tar.xz")
+
 bzip1 = load_fixture("containers/a.tar.bz2")
 bzip2 = load_fixture("containers/b.tar.bz2")
 
-TYPES = "gzip bzip2".split()
+TYPES = "gzip bzip2 xz".split()
 
 
 @pytest.fixture
-def set1(gzip1, bzip1):
-    return dict(zip(TYPES, [gzip1, bzip1]))
+def set1(gzip1, bzip1, xz1):
+    return dict(zip(TYPES, [gzip1, bzip1, xz1]))
 
 
 @pytest.fixture
-def set2(gzip2, bzip2):
-    return dict(zip(TYPES, [gzip2, bzip2]))
+def set2(gzip2, bzip2, xz2):
+    return dict(zip(TYPES, [gzip2, bzip2, xz2]))
 
 
 def expected_magic_diff(ext1, ext2):
     magic = {
         "bzip2": "bzip2 compressed data, block size = 900k\n",
         "gzip": "gzip compressed data, last modified: Sun Sep 10 22:19:44 2017, from Unix\n",
+        "xz": "XZ compressed data",
     }
+    if "xz" in (ext1, ext2):
+        if file_version_is_ge("5.40"):
+            magic["xz"] += ", checksum CRC64\n"
+        else:
+            magic["xz"] += "\n"
 
     return "@@ -1 +1 @@\n" + "-" + magic[ext1] + "+" + magic[ext2]
 
@@ -66,6 +75,7 @@ def expected_type_diff(ext1, ext2):
 # Compares same content files, but with different extensions
 
 
+@skip_unless_tools_exist("xz")
 @skip_unless_file_version_is_at_least("5.37")
 def test_equal(set1):
     for x, y in itertools.product(TYPES, TYPES):
@@ -83,6 +93,7 @@ def test_equal(set1):
 # Compares different content files with different extensions
 
 
+@skip_unless_tools_exist("xz")
 @skip_unless_file_version_is_at_least("5.37")
 def test_different(set1, set2):
     for x, y in itertools.product(TYPES, TYPES):

tests/comparators/test_elf.py

@@ -249,7 +249,7 @@ def dbgsym_differences(monkeypatch, dbgsym_dir1, dbgsym_dir2):
 @skip_unless_module_exists("debian.deb822")
 def test_differences_with_dbgsym(dbgsym_differences):
     assert dbgsym_differences.details[2].source1 == "data.tar.xz"
-    bin_details = dbgsym_differences.details[2].details[1].details[0]
+    bin_details = dbgsym_differences.details[2].details[0].details[0]
     assert bin_details.source1 == "./usr/bin/test"
     assert bin_details.details[1].source1.startswith("objdump")
     assert (
@@ -262,7 +262,7 @@ def test_differences_with_dbgsym(dbgsym_differences):
 @skip_if_binutils_does_not_support_x86()
 @skip_unless_module_exists("debian.deb822")
 def test_original_gnu_debuglink(dbgsym_differences):
-    bin_details = dbgsym_differences.details[2].details[1].details[0]
+    bin_details = dbgsym_differences.details[2].details[0].details[0]
     assert ".gnu_debuglink" in bin_details.details[2].source1
     assert_diff(bin_details.details[2], "gnu_debuglink_expected_diff")
 

tests/comparators/test_xz.py

@@ -48,10 +48,10 @@ def differences(xz1, xz2):
 
 @skip_unless_tools_exist("xz")
 def test_content_source(differences):
-    assert differences[0].source1 == "xz --list"
-    assert differences[0].source2 == "xz --list"
-    assert differences[1].source1 == "test1"
-    assert differences[1].source2 == "test2"
+    assert differences[0].source1 == "test1"
+    assert differences[0].source2 == "test2"
+    assert differences[1].source1 == "xz --list"
+    assert differences[1].source2 == "xz --list"
 
 
 @skip_unless_tools_exist("xz")
@@ -63,14 +63,16 @@ def test_content_source_without_extension(tmpdir, xz1, xz2):
     xz1 = specialize(FilesystemFile(path1))
     xz2 = specialize(FilesystemFile(path2))
     difference = xz1.compare(xz2).details
-    assert difference[1].source1 == "test1-content"
-    assert difference[1].source2 == "test2-content"
+    assert difference[0].source1 == "test1-content"
+    assert difference[0].source2 == "test2-content"
+    assert difference[1].source1 == "xz --list"
+    assert difference[1].source2 == "xz --list"
 
 
 @skip_unless_tools_exist("xz")
 def test_content_diff(differences):
-    assert_diff(differences[0], "text_xz_list")
-    assert_diff(differences[1], "text_ascii_expected_diff")
+    assert_diff(differences[0], "text_ascii_expected_diff")
+    assert_diff(differences[1], "text_xz_list")
 
 
 @skip_unless_tools_exist("xz")