This option catches unexpected mismatch when a prefix is given to
FileCheck on the command line but never matches a single line in the
test.
See http://lists.llvm.org/pipermail/llvm-dev/2020-October/146162.html
for more info.
Differential Revision: https://reviews.llvm.org/D90501
# FileCheck -enable-var-scope is enabled by default in MLIR test
# This option avoids to accidentally reuse variable across -LABEL match,
# it can be explicitly opted-in by prefixing the variable name with $
-config.environment['FILECHECK_OPTS'] = "-enable-var-scope"
+config.environment['FILECHECK_OPTS'] = "-enable-var-scope --allow-unused-prefixes=false"
# LLVM can be configured with an empty default triple