clang-diagnostic-array-bounds warning for impossible case in switch statement

[nickdesaulniers]

Bugzilla Link	36115
Version	unspecified
OS	Linux
CC	@EugeneZelenko

Extended Description

STR:

void w () {
  int y [10];
  switch (10) {
    case 300:
      y[300] = 4;
    default:
      //break;
  }
}

clang-tidy -warnings-as-errors=clang-diagnostic-array-bounds test_case.c

/tmp/test_case.c:6:7: error: array index 300 is past the end of the array (which contains 10 elements) [clang-diagnostic-array-bounds,-warnings-as-errors]
y[300] = 4;
^
/tmp/test_case.c:3:3: note: array 'y' declared here
int y [10];
^

My test case is definitely contrived, but I see effectively the same thing running clang-tidy on the Linux kernel in include/linux/signal.h:122

[EugeneZelenko]

clang-diagnostic group is alias for Clang warnings. Could you please verify that Clang produces same warning? In such cases report should be changed to Clang.

[nickdesaulniers]

Clang also produces the same warning.

[nathanchance]

mentioned in issue llvm/llvm-bugzilla-archive#51682