Proposal Details

Extend the copylock analyzer to emit a warning on the copy of the loop variable between iterations that occurs immediately before the loop's Post statement in Go >= 1.22. The requirements for the warning are when:

• a 3-clause for loop declares a loop scoped variable containing a lock type,
• the file's GoVersion is >= 1.22,
• the name of the variable is not _, and
• the Init statement of the for loop is not otherwise reported.

Example:

for _, mu := 0, (sync.Mutex{}); x < 10; x++ { // want "for loop iteration copies lock value to mu: sync.Mutex"
	_ = mu.TryLock()
}

Relevant part of the spec https://go.dev/ref/spec#For_clause :

The variable used by each subsequent iteration is declared implicitly before executing the post statement and initialized to the value of the previous iteration's variable at that moment.