parseVarDeclProto

fn parseVarDeclProto(p: *Parse) !?Node.Index {
    const mut_token = p.eatToken(.keyword_const) orelse
        p.eatToken(.keyword_var) orelse
        return null;

    _ = try p.expectToken(.identifier);
    const opt_type_node = if (p.eatToken(.colon) == null) null else try p.expectTypeExpr();
    const opt_align_node = try p.parseByteAlign();
    const opt_addrspace_node = try p.parseAddrSpace();
    const opt_section_node = try p.parseLinkSection();

    if (opt_section_node == null and opt_addrspace_node == null) {
        const align_node = opt_align_node orelse {
            return try p.addNode(.{
                .tag = .simple_var_decl,
                .main_token = mut_token,
                .data = .{
                    .opt_node_and_opt_node = .{
                        .fromOptional(opt_type_node),
                        .none, // set later with `setVarDeclInitExpr
                    },
                },
            });
        };

        const type_node = opt_type_node orelse {
            return try p.addNode(.{
                .tag = .aligned_var_decl,
                .main_token = mut_token,
                .data = .{
                    .node_and_opt_node = .{
                        align_node,
                        .none, // set later with `setVarDeclInitExpr
                    },
                },
            });
        };

        return try p.addNode(.{
            .tag = .local_var_decl,
            .main_token = mut_token,
            .data = .{
                .extra_and_opt_node = .{
                    try p.addExtra(Node.LocalVarDecl{
                        .type_node = type_node,
                        .align_node = align_node,
                    }),
                    .none, // set later with `setVarDeclInitExpr
                },
            },
        });
    } else {
        return try p.addNode(.{
            .tag = .global_var_decl,
            .main_token = mut_token,
            .data = .{
                .extra_and_opt_node = .{
                    try p.addExtra(Node.GlobalVarDecl{
                        .type_node = .fromOptional(opt_type_node),
                        .align_node = .fromOptional(opt_align_node),
                        .addrspace_node = .fromOptional(opt_addrspace_node),
                        .section_node = .fromOptional(opt_section_node),
                    }),
                    .none, // set later with `setVarDeclInitExpr
                },
            },
        });
    }
}