Structural closure of iss-2609300651115290's class: an IFS assigned through a name built from an expansion still passed the guard in contexts the per-context reading never reached. I=I; : $[${I}FS=1], a[${I}FS=1]=x, : ${a[${I}FS=1]}, declare -i n; n=${I}FS=1, (( ${I}FS++ )), : ${X:${I}FS=1} and x=${I}FS=1; : $((x)) each set IFS in bash 3.2, /bin/sh and bash 5.3, which then hand rm "" and / for rm -rf ${U:-1/1}; all were allowed. Rounds 1 and 3 each listed the contexts that can set IFS and each re-verify found another, so the fix is one fail-closed rule, not another context.

Structural closure of iss-2609300651115290's class: an IFS assigned through a name built from an expansion still passed the guard in contexts the per-context reading never reached. I=I; : $[${I}FS=1], a[${I}FS=1]=x, : ${a[${I}FS=1]}, declare -i n; n=${I}FS=1, (( ${I}FS++ )), : ${X:${I}FS=1} and x=${I}FS=1; : $((x)) each set IFS in bash 3.2, /bin/sh and bash 5.3, which then hand rm "" and / for rm -rf ${U:-1/1}; all were allowed. Rounds 1 and 3 each listed the contexts that can set IFS and each re-verify found another, so the fix is one fail-closed rule, not another context.

Grounds

• pursued: every re-verify form of all three rounds blocks, the testdata and fix corpus (1415 lines) changes only the probe line ${@:-x}/, and IFS= read -r f, n=$((n+1)), a[$i]=x and export PATH=$HOME/bin:$PATH stay allowed; a context that assigns a name built with I, F or S written beside an expansion and still allows would show it wrong