anchor build warns 'use of deprecated method AccountInfo::realloc: Use AccountInfo::resize()' pointing at #[program] — it is inside anchor-lang

A freshly generated anchor init project, with an empty initialize handler, emits:

warning: use of deprecated method `anchor_lang::prelude::AccountInfo::<'a>::realloc`:
Use AccountInfo::resize() instead
  --> programs/my-program/src/lib.rs:14:1
14 | #[program]
   | ^^^^^^^^^^
   = note: this warning originates in the attribute macro `program`

Nothing in your source calls realloc, and the span points at the #[program] attribute, which makes it look like your account layout or a resize call is at fault.

Two things explain it. The path reads anchor_lang::prelude::AccountInfo only because anchor_lang::prelude re-exports Solana's AccountInfo; it is the same type from solana-account-info. And the actual call site is inside anchor-lang itself (its internal helper used by code the #[program] macro expands), which is why the diagnostic is attributed to the macro invocation rather than to a line you wrote. AccountInfo::realloc was deprecated in favour of resize in solana-account-info 2.3.0, so any Anchor release predating the upstream rename produces this warning against newer SDKs.

There is no fix in user code: it is cosmetic and cannot be silenced by changing your handler. Either upgrade Anchor to a release that switched to resize, or ignore it. If it must be quiet for a -D warnings CI gate, allow it at the crate root (#![allow(deprecated)]), accepting that this masks genuine deprecations in your own code too.

Observed with anchor-cli 0.31.1, Solana CLI 2.2.20, rustc 1.88.0; expect it to disappear in later Anchor releases.

Source: adapted from a Stack Exchange answer by abelmarnk (question by Russo), https://solana.stackexchange.com/questions/22979/use-of-deprecated-method-anchor-langpreludeaccountinfoarealloc-use — CC BY-SA 4.0