This was only relevant so far for the benchmark suite as it would
recycle Expr for repetitions. However, the append is unnecessary as
each node is only inspected once when populating iterators, and
population must always start from scratch.
This also introduces error checking during benchmarks and fixes the so
far undetected test errors during benchmarking.
Also, remove a style nit (two golint warnings less…).
Also, remove unused `providers` field in targetSet.
If the config file changes, we recreate all providers (by calling
`providersFromConfig`) and retrieve all targets anew from the newly
created providers. From that perspective, it cannot harm to clean up
the target group map in the targetSet. Not doing so (as it was the
case so far) keeps stale targets around. This mattered if an existing
key in the target group map was not overwritten in the initial fetch
of all targets from the providers. Examples where that mattered:
```
scrape_configs:
- job_name: "foo"
static_configs:
- targets: ["foo:9090"]
- targets: ["bar:9090"]
```
updated to:
```
scrape_configs:
- job_name: "foo"
static_configs:
- targets: ["foo:9090"]
```
`bar:9090` would still be monitored. (The static provider just
enumerates the target groups. If the number of target groups
decreases, the old ones stay around.
```
scrape_configs:
- job_name: "foo"
dns_sd_configs:
- names:
- "srv.name.one.example.org"
```
updated to:
```
scrape_configs:
- job_name: "foo"
dns_sd_configs:
- names:
- "srv.name.two.example.org"
```
Now both SRV records are still monitored. The SRV name is part of the
key in the target group map, thus the new one is just added and the
old ane stays around.
Obviously, this should have tests, and should have tests before, not
only for this case. This is the quick fix. I have created
https://github.com/prometheus/prometheus/issues/1906 to track test
creation.
Fixes https://github.com/prometheus/prometheus/issues/1610 .
0 is considered an invalid interval by time.NewTicker() and will cause a
panic if control reaches that point. Given the vagaries of timekeeping,
this may occasionally happen and make this test unstable.
Apart from not trying to send a newline in a HTTP header,
this also allows Prometheus to build and pass tests with Go 1.7,
which features stricter checking of HTTP headers.
