MessageProcessor::process_message() returns the accounts data len delta, and the bank uses the value to update its accounts_data_len field

[brooksprumo]

Problem

The bank doesn't get accounts data len changes from MessageProcessor, so it cannot account for any changes.

For more context see the main issue #21604

Summary of Changes

MessageProcessor::process_message() returns the accounts data len delta, and the bank uses the value to update its accounts_data_len field

[codecov]

Codecov Report

Merging #21807 (85235a4) into master (eeb97fe) will decrease coverage by 0.0%.
The diff coverage is 81.2%.

@@            Coverage Diff            @@
##           master   #21807     +/-   ##
=========================================
- Coverage    81.3%    81.3%   -0.1%     
=========================================
  Files         515      515             
  Lines      144033   144044     +11     
=========================================
- Hits       117126   117111     -15     
- Misses      26907    26933     +26     

[brooksprumo]

Right now just return a default value. The next PR (here) will fill this in with real values.

[jackcmay]

Are you planning to return the updated meter value?

[brooksprumo]

Yep! Here's a snippet from the next PR:

solana/runtime/src/message_processor.rs

Lines 130 to 132 in 3393d2e

	Ok(ProcessedMessageInfo {
	accounts_data_len_delta: invoke_context.get_accounts_data_meter().take().consumed(),
	})

[brooksprumo]

@jackcmay Let me know if there's any questions on this PR, or if you'd like me to run it by anyone else. TIA!

[Lichtso]

As already discussed on Slack, this part here will most likely change when accounts are passed back directly (not by Rc through the parameters). Because the accounts need to be always returned and this struct only on success, it would become somewhat messy. But I am not sure yet, what a good solution would be.

[jackcmay]

Remind why we are passing the accounts back in the return value rather then shared access with Rc?

[Lichtso]

Rc around accounts won't work anymore in ABIv2 (see #21706 and #21927).

[jackcmay]

I didn't see an explanation in those prs as to why we must get rid of Rc

[Lichtso]

You are right, I removed that when splitting the PRs, will add it back in.
The short version is that we can't serialize a Rc, so we would have to wrap / unwrap it twice in process_message() which is completely unnecessary. And ABIv2 is all about getting rid of such unnecessary copy steps.