[clang] [llvm] Reland "[Utils] Add new --update-tests flag to llvm-lit" (PR #153821)

[Min-Yih Hsu via cfe-commits]

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@@ -0,0 +1,39 @@
+import shutil
+
+
+def get_source_and_target(a, b):
+    """
+    Try to figure out which file is the test output and which is the reference.
+    """
+    expected_suffix = ".expected"
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mshockwave wrote:

please document these heuristics somewhere.

https://github.com/llvm/llvm-project/pull/153821