Imported pallet and got "use codec::alloc::vec;"

Question

I work on a pallet with interior dispatch mutability where I need to make calls cancel_as_multi and as_multi and after importing contracts pallet, compiler forces me to change contracts pallet. But I do not want to change contracts pallet, and I completely do not understand why compiler forces me to implement those changes. Here is what I got from a compiler:

   Compiling pallet-contracts v4.0.0-dev (/home/tomek/workspaces/polkadot-sdk/substrate/frame/contracts) error: cannot find macro `vec` in this scope    --> substrate/frame/contracts/src/wasm/mod.rs:272:7
    | 272 |                         vec![code_hash],
    |                         ^^^
    | help: consider importing one of these items
    | 30  + use codec::alloc::vec;
    | 30  + use crate::vec;
    | 30  + use scale_info::prelude::vec;
    | 30  + use sp_api::vec;
    |
      and 1 other candidate

This kind of errors I got many, many more but all connected to use codec::alloc::vec;. I have no idea why, can anyone explain the way? I do not understand the mechanism that works behind. I ask the question because I was assuming, that just the fact of importing a pallet should not induce any changes in the imported pallet.

Answer 1

Sometimes, if you forget to include xxx/std in the features, you will encounter this error.