C array element designators [i] = v + [] size inference from designators

• Type: bug (cfront init lowering). Track C. Slice of [[bug-c-init-designated-and-nested]].
• Found: 2026-07-06 c-testsuite; scoped during that ticket's triage.

Cases

• 00092 int a[] = {5, [2] = 2, 3}; — designator + size inference (a[1]==0, a[3]==3, sizeof = 4 ints)
• 00147 int arr[3] = {[2] = 2, [0] = 0, [1] = 1}; — out-of-order
• 00148 struct S arr[2] = {[1] = {3, 4}, [0] = {1, 2}}; — array-of-struct designators (composes with [[bug-c-init-struct-designators]])

Symptom

[idx] = designator ignored → sequential fill → wrong slots; and for [], size = element-count instead of max designated index + 1, so both values and sizeof are wrong.

Fix (a "current element index" cursor)

Before each element, if the stream is [ constexpr ] =, evaluate the index, set the running ei to it (consume [ ] =); else keep sequential ei. Track maxEi and, for an unsized [], set arrLen = maxEi + 1.

• Local: the array loop in ParseCLocalDeclAST ~cparser.inc:2365 and the arrLen/recArrInitCount size logic ~2474.
• Global: the flat-int PendingInit array path ~cparser.inc:3731 (uses PendingInitElem = ei).

Gate

00092/00147 exit 0 (00148 needs struct designators too); drop from test/c-conformance/pxx.skip; regression test; make test + self-host.

Log

• 2026-07-06 — resolved, commit c0abec31.