Delay parsing of date/time strings until needed

[joelegasse]

The current code would compare every string literal it crossed and tried
to coerce them to time literals if the looked like date/time strings.

The only time the TimeLiteral was used is when comparing to the the
'time' value in a where clause. This change moves the string parsing
code until we attempt to compare 'time' to a string, at which point we
know we need/want a TimeLiteral, and not just an ordinary string.

Fixes #6727

\cc @beckettsean @benbjohnson @jsternberg

Required for all non-trivial PRs

• Rebased/mergable
• Tests pass
• CHANGELOG.md updated

[e-dard]

LGTM 👍

[benbjohnson]

The code generally lgtm. 👍 I'm surprised it didn't take a little more code to change.

There seems to be a breaking test in the CLI though:

Unknown precision "". Please use rfc3339, h, m, s, ms, u or ns.
Visit https://enterprise.influxdata.com to register for updates, InfluxDB server management, and monitoring.
Connected to http://127.0.0.1:32988 version x.x
InfluxDB shell version: y.y
> panic: close of closed channel

goroutine 51 [running]:
panic(0x7d2b60, 0xc8201380e0)
    /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/influxdata/influxdb/cmd/influx/cli_test.TestRunCLI.func1(0xc820108000)
    /root/go/src/github.com/influxdata/influxdb/cmd/influx/cli/cli_test.go:51 +0x28
created by github.com/influxdata/influxdb/cmd/influx/cli_test.TestRunCLI
    /root/go/src/github.com/influxdata/influxdb/cmd/influx/cli/cli_test.go:52 +0x257

[joelegasse]

I was also really surprised that the change was that small. I started by removing the regex matching, and making all strings StringLiterals, and then only one thing broke... so I put the conversion code there. :-)

The CLI test passed on rebuild, I'm guessing there's a race-encouraging test in there somewhere.

[beckettsean]

Thanks for the very quick fix!