Should a version indicator be encoded into `Cargo.lock`

[alexcrichton]

The Cargo.lock format is changing over time (and is practically guaranteed to continue changing) and the most recent change has brought up ideas again about possibly encoding a version number into Cargo.lock. There's a number of comments on that thread weighing some pros and cons (including this one).

One possible way to implement this would be to add a field to the [metadata] table. Every version of Cargo ever preserves the [metadata] table, and so we can add a version number in there practically any time and have it preserved by older Cargo while recognized by newer Cargo.

[mathstuf]

An alternative would be to add flags to newer releases to write out old formats as well.

[est31]

PR #8522 has been opened to add such version numbers.

[epage]

At this point we are on version 3 of lock files. Any reason to not close this issue?

[est31]

Yeah #8522 has added that number as 3. The issue can be closed.