sql: also handle ESCAPE characters properly in COPY machine

[otan]

Release justification: critical bug fix to existing functionality

Release note (bug fix): Previously, escaping a double quote (") with
COPY in CSV mode could ignore all subsequent lines in the same COPY
if an ESCAPE clause were specified. This is now resolved.

[cockroach-teamcity]

This change is 

[ajstorm]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan and @rafiss)

---

pkg/sql/copy.go line 538 at r1 (raw file):

		} else {
			// Otherwise, we have to do a more involved count of quotes and
			// ignore any escaped quotes for counting.

Nit: Can we build out this comment a bit more, perhaps with a short example? It took me a bit to understand what's going on below, and I worry others who encounter this code for the first time will also be confused.

---

pkg/sql/copy.go line 541 at r1 (raw file):

			isEscaped := false
			for _, ch := range line {
				if isEscaped {

Nit: I'm wondering if this would be more readable if you called this variable skipNextChar and then added a comment below saying that "We found a rune which matches the specified escape value. This means we need to skip the next character, as it's been escaped"?

[ajstorm]

This now. I'm wondering if as a follow on item in stability we should add far more robust (randomized?) testing for parsing in COPY. I worry that this may not be the only bug lingering.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @rafiss)

[rafiss]

nice find. i don't think backports are needed since v22.2 is the first release where ESCAPE is supported.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @ajstorm)

[rafiss]

oh, i forgot that we backported ESCAPE

[daniel-crlabs]

This affects customers on cockroach cloud as well, see linked ticket.

[otan]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)