[llvm] [lit] Add JSON diffing support to lit (PR #177513)

[Henrik G. Olsson via llvm-commits]

================
@@ -2,76 +2,291 @@
 import sys
 import difflib
 import getopt
+import re
 
-
-class CommandLineArguments:
-    def __init__(self):
-        self.ignore_extra_keys = False
-        self.context = 3
-        self.expected_file = None
-        self.actual_file = None
+# ==============================================================================
+# Utility Functions
+# ==============================================================================
 
 
-def fail(msg, exit_code):
-    sys.stderr.write(msg)
-    sys.stderr.write("\n")
+def fail(exit_code, *messages):
+    """Print error messages to stderr and exit with the given code."""
+    for msg in messages:
+        sys.stderr.write(msg)
+        sys.stderr.write("\n")
     sys.exit(exit_code)
 
 
-def readJson(filepath):
-    def checkDuplicateKeys(pairs):
-        keys = [key for (key, value) in pairs]
-        seen = set()
-        duplicates = set()
+# ==============================================================================
+# Match Result Classes
+# ==============================================================================
 
-        for key in keys:
-            if key in seen:
-                duplicates.add(key)
+
+class MatchResult:
----------------
hnrklssn wrote:

How well does this work with the context of a mismatch? If I have a 200 line JSON, will I be able to easily find which field the mismatch was on?

https://github.com/llvm/llvm-project/pull/177513