[hlsl-out] Fix fallthrough in switch statements (for FXC)

[teoxoy]

Fixes FXC error X3537: Fall-throughs in switch statements are not allowed by emitting the statements of the following case blocks (the ones the fallthrough was supposed to reach).

[jimblandy]

Looks good. Just one suggestion.

[jimblandy]

I think this could be simplified a bit:

Suggested change

	let curr_len = i + 1;
	let end_case_idx = curr_len
	+ cases
	.iter()
	.skip(curr_len)
	.position(|case| !case.fall_through)
	.unwrap();
	let indent_level_3 = indent_level_2.next();
	for case in &cases[i..=end_case_idx] {
	writeln!(self.out, "{}{{", indent_level_2)?;
	for sta in case.body.iter() {
	self.write_stmt(module, sta, func_ctx, indent_level_3)?;
	}
	writeln!(self.out, "{}}}", indent_level_2)?;
	}
	let rest = &cases[i..];
	let fallthrough_count = rest
	.iter()
	.position(|case| !case.fall_through)
	.unwrap();
	// Include the final, non-`fall_through` case.
	let fallthrough = &rest[..=fallthrough_count];
	let indent_level_3 = indent_level_2.next();
	for case in fallthrough {
	writeln!(self.out, "{}{{", indent_level_2)?;
	for sta in case.body.iter() {
	self.write_stmt(module, sta, func_ctx, indent_level_3)?;
	}
	writeln!(self.out, "{}}}", indent_level_2)?;
	}

[teoxoy]

I find the naming to be slightly more confusing here since rest and fallthrough contain the first case as well. Getting fallthrough_count should also skip the first element (since it's the first case) and add one at the end.

I tried to make it more clear as well without much luck...

[jimblandy]

Pair with the above suggestion:

Suggested change

	let last_case = &cases[end_case_idx];
	if last_case.body.last().map_or(true, |s| !s.is_terminator()) {
	writeln!(self.out, "{}break;", indent_level_2)?;
	}
	let last_case = &fallthrough[fallthrough_count];
	if last_case.body.last().map_or(true, |s| !s.is_terminator()) {
	writeln!(self.out, "{}break;", indent_level_2)?;
	}

[jimblandy]

You know, I should just keep minor style stuff like that to myself. Merging as posted.