lang: Fix account try_from usage

[acheroncrypto]

Problem

Using try_from in the instruction handler:

pub fn try_from(ctx: Context<TryFrom>) -> Result<()> {
    Account::<MyAccount>::try_from(&ctx.accounts.my_account)?;
    Ok(())
}

results in:

error: lifetime may not live long enough
  --> programs/try-from/src/lib.rs:15:9
   |
14 |     pub fn try_from(ctx: Context<TryFrom>) -> Result<()> {
   |                     ---
   |                     |
   |                     has type `anchor_lang::context::Context<'_, '1, '_, '_, TryFrom<'_>>`
   |                     has type `anchor_lang::context::Context<'_, '_, '_, '_, TryFrom<'2>>`
15 |         Account::<MyAccount>::try_from(&ctx.accounts.my_account)?;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`

Details

Ideally, the fix would be limited to Anchor internals without needing a breaking change to the users. However, this is difficult to achieve because #2656 added the same lifetime requirement for the AccountInfo references:

anchor/lang/src/accounts/account.rs

Lines 226 to 229 in c93b33a

	pub struct Account<'info, T: AccountSerialize + AccountDeserialize + Clone> {
	account: T,
	info: &'info AccountInfo<'info>,
	}

The info: &'info AccountInfo<'info> part is incompatible with Anchor's codegen because accounts passed to the context has a shorter lifetime than the AccountInfo's internal lifetime. While the lifetime annotations are incorrect based on Anchor's codegen, it's also not accidental. To properly annotate these lifetimes, we'd have to add another lifetime to the Account type(and all other account types) which would significantly hinder the developer experience since it's a public API.

In short, this problem is caused by annoting the same lifetimes in places where it's technically incorrect but we're doing so in order to not have multiple lifetimes in account types.

One possible solution for this problem is to elide the lifetimes by using core::mem::transmute. Using transmute is heavily discouraged but my understanding is, this should be safe to do in this case because both accounts lifetime and the AccountInfo's internal lifetime live longer than the user's instruction handler.

Usage

try_from!(Account::<MyAccount>, ctx.accounts.my_account)

Summary of changes

• Add a test program for try_from usage
• Add try_from! macro

[vercel]

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