better error for mistakely doing && instead of and

[andrewrk]

Here's an example use case thanks to @vegecode:

const std = @import("std");
const assert = std.debug.assert;

pub const CursorPos = struct {
    row_pos: usize,
    col_pos: usize,
};

fn scanRowColumnPositionResponse(response: []const u8) !CursorPos {
    // expected response: 'ESC' '[' rows ';' columns 'R'
    if (mem.compare(u8, response, ESC ++ "[") != mem.Compare.Equal) {
        return VTError.UnexpectedResponse;
    }

    const delimiter_index = mem.indexOf(u8, response, ";") orelse return VTError.UnexpectedResponse;
    const row_pos = try fmt.parseUnsigned(usize, response[2 .. delimiter_index - 1], 10);
    const col_pos = try fmt.parseUnsigned(usize, response[delimiter_index + 1 ..], 10);

    return CursorPos{
        .row_pos = row_pos,
        .col_pos = col_pos,
    };
}

test "scan row/column position response" {
    const ESC = "";
    const ret1 = scanRowColumnPositionResponse((ESC ++ "[20;30")[0..]) catch unreachable;
    assert(ret1.row_pos == 20 && ret1.col_pos == 30);
}

The error you get is:

test.zig:28:28: error: integer value 20 cannot be implicitly casted to type '*const usize'
    assert(ret1.row_pos == 20 && ret1.col_pos == 30);
                           ^

Which is not at all clear what's actually happening: that the programmer accidentally used && instead of and.

I believe that & followed by another & would never be valid semantically, so the parser can reject this and say "did you mean and?"

[daurnimator]

Yes please! I've made the same mistake (see #1737)

[emekoi]

related too: #1560.