[ASDAlexander77]

Problem

• n ?? -1 for n?: number:
  • it tested the value's truthiness, so f(0) returned -1;
  • it compared the value with null through a cast to a pointer, which warned invalid cast from 'f64' to '!llvm.ptr';
  • its type stayed number | undefined.
• s ?? "x" for s?: string, and y ?? 8 for number | null, did not compile.
• 0 === null was true, because null was read as 0. The same happened for an optional number holding 0.
• x === null for x: 0 | 1 | 42 failed in LLVM lowering ('llvm.icmp' op requires all operands to have the same type).
• Every generator yielding a number or another value type warned using casting to undefined value. The warning came from the generator's finished {value: undefined, done: true}.

Fix

• ?? now tests whether the left side is null or undefined according to its type (mlirGenIsNullish):
  • an optional is nullish when it has no value, and its value is tested only when there is one;
  • a value type is never nullish;
  • a union, any or a pointer type is compared with null and with undefined.
• The type of a ?? b is a's type without null and undefined, combined with b's. When a can only be nullish, it is b's type.
• Compares with null / undefined whose answer the type already decides are folded (foldNullishCompare):
  • a value type is never equal to either;
  • an optional value type is never === null;
  • an optional value type is == null exactly when it has no value.
• Refactor: the value-level part of mlirGen(BinaryExpression) is now mlirGenBinaryValues, so ?? uses the same compare. Behaviour is unchanged.
• The generator's finished value, for a value type, takes its zero directly (InternalFlags::GeneratorDoneValue). That is what the cast already lowered to. Other types keep the cast, so a string still gets the text "undefined".

Tests

• New 00nullish_values.ts, run as compile and jit. It passes under gc, rc and none.
• Release suite: 3347/3347.
• DefaultLib built with this compiler: 159/159 compiled and 159/159 under JIT.
• Not run: Debug builds, x86, -mm=own.

🤖 Generated with Claude Code