travis: support .xz compressed golden reference files

Some tests may by necessity generate very large output files. Allow
.xz compression of the reference files to avoid bloating the git
repository too much. The committer of very large files will need to
carefully consider the xz options used to maximize compressibility
especially of highly regular files.

This commit was AI-assisted (Copilot/Claude Sonnet 5).

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Author: H. Peter Anvin (Intel)

travis/nasm-t.py

@@ -3,9 +3,9 @@
 import subprocess
 import argparse
 import difflib
-import filecmp
 import fnmatch
 import json
+import lzma
 import sys
 import re
 import os
@@ -115,11 +115,22 @@
     parser.print_help()
     sys.exit(64)
 
+#
+# Read a reference/golden file, transparently decompressing it if
+# only a "<path>.xz" variant is present.  This lets very large but
+# highly repetitive reference files (e.g. object files with tens of
+# thousands of sections) be stored compressed instead of bloating
+# the git repository.
+def read_ref_file(path):
+    if os.path.exists(path):
+        with open(path, "rb") as f:
+            return f.read()
+    xz_path = path + '.xz'
+    with lzma.open(xz_path, "rb") as f:
+        return f.read()
+
 def read_stdfile(path):
-    with open(path, "rb") as f:
-        data = f.read().decode("utf-8","replace")
-        f.close()
-        return data
+    return read_ref_file(path).decode("utf-8","replace")
 
 #
 # Check if descriptor has mandatory fields
@@ -265,30 +276,32 @@ def test_updated(test):
     print("=== Test %s UPDATED ===" % (test))
     return True
 
-def hexdump(path):
+def hexdump(data):
     dump = ''
     addr = 0
-    with open(path, 'rb') as f:
-        while b := f.read(16):
-            dump += "%08x  " % (addr)
-            for i in range(16):
-                if (i == 8):
-                    dump += " -"
-                if (i >= len(b)):
-                    dump += "   "
-                else:
-                    dump += " %02x" % b[i]
-            dump += "  |"
-            for i in range(16):
-                if (i >= len(b)):
-                    c = ord(' ')
-                else:
-                    c = b[i]
-                if (c < 32 or c > 126):
-                    c = ord('.')
-                dump += chr(c)
-            dump += "|\n";
-            addr += 16
+    pos = 0
+    while pos < len(data):
+        b = data[pos:pos+16]
+        dump += "%08x  " % (addr)
+        for i in range(16):
+            if (i == 8):
+                dump += " -"
+            if (i >= len(b)):
+                dump += "   "
+            else:
+                dump += " %02x" % b[i]
+        dump += "  |"
+        for i in range(16):
+            if (i >= len(b)):
+                c = ord(' ')
+            else:
+                c = b[i]
+            if (c < 32 or c > 126):
+                c = ord('.')
+            dump += chr(c)
+        dump += "|\n";
+        addr += 16
+        pos += 16
     return dump
 
 def show_std(stdname, data):
@@ -314,12 +327,9 @@ def cmp_std(from_name, from_data, match_name, match_data):
         return False
     return True
 
-def show_diff(test, patha, pathb):
-    try:
-        sa = hexdump(patha)
-        sb = hexdump(pathb)
-    except OSError:
-        return test_fail(test, "Can't create dumps")
+def show_diff(test, patha, adata, pathb, bdata):
+    sa = hexdump(adata)
+    sb = hexdump(bdata)
 
     print("\t--- hexdump %s" % (patha))
     for i in sa.split("\n"):
@@ -424,8 +434,14 @@ def test_run(desc):
             if desc['_wait'] == 1:
                 continue
             print("\tComparing %s %s" % (output, match))
-            if filecmp.cmp(match, output) == False:
-                show_diff(desc['_test-name'], match, output)
+            try:
+                match_data = read_ref_file(match)
+                with open(output, "rb") as f:
+                    out_data = f.read()
+            except OSError:
+                return test_fail(desc['_test-name'], "Can't read " + match + " or " + output)
+            if match_data != out_data:
+                show_diff(desc['_test-name'], match, match_data, output, out_data)
                 return test_fail(desc['_test-name'], match + " and " + output + " files are different")
         elif 'stdout' in t:
             print("\tComparing stdout")
@@ -464,6 +480,38 @@ def test_run(desc):
 
     return test_pass(desc['_test-name'])
 
+#
+# Compress data for a reference file, trying a couple of xz filter
+# chains suited to different kinds of content (plain text/binary vs.
+# highly repetitive fixed-stride records), and keep whichever is
+# smallest.
+def compress_ref_data(data):
+    candidates = [lzma.compress(data, preset = 9 | lzma.PRESET_EXTREME)]
+    if len(data) >= 4096:
+        filters = [
+            {'id': lzma.FILTER_DELTA, 'dist': 256},
+            {'id': lzma.FILTER_LZMA2, 'preset': 9 | lzma.PRESET_EXTREME},
+        ]
+        try:
+            candidates.append(lzma.compress(data, format = lzma.FORMAT_XZ,
+                                             filters = filters))
+        except lzma.LZMAError:
+            pass
+    return min(candidates, key = len)
+
+#
+# Write out a reference file.  If a compressed "<path>.xz" copy is
+# already checked in (and no plaintext copy exists), keep storing it
+# compressed; otherwise write plaintext as before.
+def write_ref_file(path, data):
+    xz_path = path + '.xz'
+    if os.path.exists(xz_path) and not os.path.exists(path):
+        with open(xz_path, "wb") as f:
+            f.write(compress_ref_data(data))
+    else:
+        with open(path, "wb") as f:
+            f.write(data)
+
 #
 # Compile sources and generate new targets
 def test_update(desc):
@@ -483,19 +531,18 @@ def test_update(desc):
             output = desc['_base-dir'] + os.sep + t['output']
             match = desc['_base-dir'] + os.sep + t['match']
             print("\tMoving %s to %s" % (output, match))
-            os.rename(output, match)
+            with open(output, "rb") as f:
+                data = f.read()
+            os.remove(output)
+            write_ref_file(match, data)
         if 'stdout' in t:
             match = desc['_base-dir'] + os.sep + t['stdout']
             print("\tMoving %s to %s" % ('stdout', match))
-            with open(match, "wb") as f:
-                f.write(stdout.encode("utf-8"))
-                f.close()
+            write_ref_file(match, stdout.encode("utf-8"))
         if 'stderr' in t:
             match = desc['_base-dir'] + os.sep + t['stderr']
             print("\tMoving %s to %s" % ('stderr', match))
-            with open(match, "wb") as f:
-                f.write(stderr.encode("utf-8"))
-                f.close()
+            write_ref_file(match, stderr.encode("utf-8"))
 
     return test_updated(desc['_test-name'])