elf.py: remove StaticLibFile; ArFile.compare_details() is much better

Remove the old code in the StaticLibFile class as it now duplicates the
recursion in ArFile.compare_details() in a much inferior way. Fixes
issue #64, see the multiple use cases there and in the next commit
adding tests.

The patch header line in the test output is decremented one line because
when run on .a files readelf inserted headings like this:

  In archive test1.a:

Signed-off-by: Marc Herbert <Marc.Herbert@gmail.com>

diffoscope/comparators/__init__.py

@@ -55,7 +55,6 @@ class ComparatorManager(object):
         ('elf.ElfFile',),
         ('macho.MachoFile',),
         ('fsimage.FsImageFile',),
-        ('elf.StaticLibFile',),
         ('llvm.LlvmBitCodeFile',),
         ('sqlite.Sqlite3Database',),
         ('wasm.WasmFile',),

diffoscope/comparators/ar.py

@@ -31,10 +31,9 @@ from .utils.libarchive import LibarchiveContainer, list_libarchive
 logger = logging.getLogger(__name__)
 
 
-# TODO: this would also be useful for Go archives. Currently those are handled
-# by StaticLibFile, but then readelf complains with "Error: Not an ELF file".
-# ArFile gives slightly more reasonable output, e.g. a readable plain diff of
-# the __.PKGDEF member which is just a text file containing the Go interface.
+# For Go archives this gives a readable plain diff of the __.PKGDEF
+# member which is just a text file containing the Go interface.
+# TODO: add Go tests and more recursion.
 
 
 class ArContainer(LibarchiveContainer):

diffoscope/comparators/elf.py

@@ -623,23 +623,3 @@ class ElfFile(File):
 
     def compare_details(self, other, source=None):
         return _compare_elf_data(self.path, other.path)
-
-
-class StaticLibFile(File):
-    DESCRIPTION = "statically-linked binaries"
-    CONTAINER_CLASS = ElfContainer
-    FILE_TYPE_RE = re.compile(r'\bar archive\b')
-    FILE_EXTENSION_SUFFIX = '.a'
-
-    def compare_details(self, other, source=None):
-        differences = [
-            Difference.from_text_readers(
-                list_libarchive(self.path),
-                list_libarchive(other.path),
-                self.path,
-                other.path,
-                source="file list",
-            )
-        ]
-        differences.extend(_compare_elf_data(self.path, other.path))
-        return differences

tests/comparators/test_elf.py

@@ -23,7 +23,8 @@ import os.path
 import subprocess
 
 from diffoscope.config import Config
-from diffoscope.comparators.elf import ElfFile, StaticLibFile
+from diffoscope.comparators.ar import ArFile
+from diffoscope.comparators.elf import ElfFile
 from diffoscope.comparators.binary import FilesystemFile
 from diffoscope.comparators.directory import FilesystemDirectory
 from diffoscope.comparators.missing_file import MissingFile
@@ -108,7 +109,7 @@ def lib2():
 
 
 def test_lib_identification(lib1):
-    assert isinstance(lib1, StaticLibFile)
+    assert isinstance(lib1, ArFile)
 
 
 def test_lib_no_differences(lib1):
@@ -129,9 +130,9 @@ def test_lib_differences(lib_differences):
     assert lib_differences[0].source1 == 'file list'
     expected_metadata_diff = get_data('elf_lib_metadata_expected_diff')
     assert lib_differences[0].unified_diff == expected_metadata_diff
-    assert 'objdump' in lib_differences[1].source1
+    assert 'objdump' in lib_differences[1].details[0].source1
     expected_objdump_diff = get_data('elf_lib_objdump_expected_diff')
-    assert lib_differences[1].unified_diff == expected_objdump_diff
+    assert lib_differences[1].details[0].unified_diff == expected_objdump_diff
 
 
 @skip_unless_tools_exist('readelf', 'objdump')

tests/data/elf_lib_objdump_expected_diff

-@@ -4,10 +4,10 @@
+@@ -3,10 +3,10 @@
  
  Disassembly of section .text: