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

[Henrik G. Olsson via llvm-commits]

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@@ -0,0 +1,7 @@
+# Test absence pattern (@!)
+# Test that keys marked with @! should not exist in actual JSON
+# RUN: json-diff %S/patterns-absence-expected.json %S/patterns-absence-actual.json
+
+# Test that presence of key marked with @! causes failure
+# RUN: not json-diff %S/patterns-absence-fail-expected.json %S/patterns-absence-fail-actual.json 2>&1 | FileCheck --check-prefix=FAIL %s
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hnrklssn wrote:

Does `@!` make sense without `--ignore-extra-keys`? Regardless, I think we should test that combination as well.

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