A switch's default clause falls through like any other clause

[ASDAlexander77]

Problem

A default clause without a break never fell through into the clauses after it. It jumped straight out of the switch:

function t(x: number) {
    let r = "";
    switch (x) {
        default: r += "q";   // fallthrough
        case 6:  r += "x";   // fallthrough
        case 8:  r += "y"; break;
    }
    return r;
}
t(100)   // "q", expected "qxy"

The same happened with default in the middle. docs/bugs/testFallThrough.ts reports fail: q !== qxy.

Cause

mlirGenSwitchCase ends each clause body with a branch to the merge block. If the body has no break, that branch is put in pendingBranches so that the next clause points it at its own body. The condition was !hasBreak && !isDefaultCase, so a default body always branched to the end of the switch.

Fix

Drop !isDefaultCase. When default is the last clause, its pending branch is never re-pointed and keeps the merge block it was created with, the same as for a last case.

Testing

• New 00switch_default_fallthrough.ts (compile + JIT + rc/none corpus): default first, in the middle, and last, plus default with break. The current release fails with assertion failed: defaultFirst(100).
• docs/bugs/testFallThrough.ts now prints all OK.
• Full ctest: 3919/3919 pass.

🤖 Generated with Claude Code