expectVarAssignStatement

fn expectVarAssignStatement(p: *Parse, comptime_token: ?TokenIndex) !Node.Index {
    const scratch_top = p.scratch.items.len;
    defer p.scratch.shrinkRetainingCapacity(scratch_top);

    while (true) {
        const opt_var_decl_proto = try p.parseVarDeclProto();
        if (opt_var_decl_proto) |var_decl| {
            try p.scratch.append(p.gpa, var_decl);
        } else {
            const expr = try p.parseExpr() orelse {
                if (p.scratch.items.len == scratch_top) {
                    // We parsed nothing
                    return p.fail(.expected_statement);
                } else {
                    // We've had at least one LHS, but had a bad comma
                    return p.fail(.expected_expr_or_var_decl);
                }
            };
            try p.scratch.append(p.gpa, expr);
        }
        _ = p.eatToken(.comma) orelse break;
    }

    const lhs_count = p.scratch.items.len - scratch_top;
    assert(lhs_count > 0);

    const equal_token = p.eatToken(.equal) orelse eql: {
        if (lhs_count > 1) {
            // Definitely a destructure, so allow recovering from ==
            if (p.eatToken(.equal_equal)) |tok| {
                try p.warnMsg(.{ .tag = .wrong_equal_var_decl, .token = tok });
                break :eql tok;
            }
            return p.failExpected(.equal);
        }
        const lhs = p.scratch.items[scratch_top];
        switch (p.nodeTag(lhs)) {
            .global_var_decl, .local_var_decl, .simple_var_decl, .aligned_var_decl => {
                // Definitely a var decl, so allow recovering from ==
                if (p.eatToken(.equal_equal)) |tok| {
                    try p.warnMsg(.{ .tag = .wrong_equal_var_decl, .token = tok });
                    break :eql tok;
                }
                return p.failExpected(.equal);
            },
            else => {},
        }

        const expr = try p.finishAssignExpr(lhs);
        try p.expectSemicolon(.expected_semi_after_stmt, true);
        if (comptime_token) |t| {
            return p.addNode(.{
                .tag = .@"comptime",
                .main_token = t,
                .data = .{ .node = expr },
            });
        } else {
            return expr;
        }
    };

    const rhs = try p.expectExpr();
    try p.expectSemicolon(.expected_semi_after_stmt, true);

    if (lhs_count == 1) {
        const lhs = p.scratch.items[scratch_top];
        switch (p.nodeTag(lhs)) {
            .simple_var_decl, .aligned_var_decl, .local_var_decl, .global_var_decl => {
                p.setVarDeclInitExpr(lhs, rhs.toOptional());
                // Don't need to wrap in comptime
                return lhs;
            },
            else => {},
        }
        const expr = try p.addNode(.{
            .tag = .assign,
            .main_token = equal_token,
            .data = .{ .node_and_node = .{
                lhs,
                rhs,
            } },
        });
        if (comptime_token) |t| {
            return p.addNode(.{
                .tag = .@"comptime",
                .main_token = t,
                .data = .{ .node = expr },
            });
        } else {
            return expr;
        }
    }

    // An actual destructure! No need for any `comptime` wrapper here.

    const extra_start: ExtraIndex = @fromBackingInt(@intCast(p.extra_data.items.len));
    try p.extra_data.ensureUnusedCapacity(p.gpa, lhs_count + 1);
    p.extra_data.appendAssumeCapacity(@intCast(lhs_count));
    p.extra_data.appendSliceAssumeCapacity(@ptrCast(p.scratch.items[scratch_top..]));

    return p.addNode(.{
        .tag = .assign_destructure,
        .main_token = equal_token,
        .data = .{ .extra_and_node = .{
            extra_start,
            rhs,
        } },
    });
}