MetricVec was already exported in early versions of this library, but
nobody really used it to implement vectors of custom Metric
implementations. Now #796 has shown up with a fairly special use case
for which I'd prefer a custom implementation of a special
"auto-sampling histogram" outside of this library. Therefore, I'd like
to reinstate support for creating vectors of custom Metric
implementations.
I played around for quite some while with the option of a separate
package providing the tools one would need to create vectors of custom
Metric implementations. However, with the current structure of the
prometheus/client_golang/prometheus package, this leads to a lot of
complications with circular dependencies. (The new package would need
the primitives from the prometheus package, while the existing metric
vectors like GaugeVec need to import the new vector package to not
duplicate the implementation. Separating vector types from the main
prometheus package is out of the question at this point because that
would be a breaking change.)
Signed-off-by: beorn7 <beorn@grafana.com>
`github.com/golang/protobuf/proto` is deprecated in lieu of
`google.golang.org/protobuf/proto`. However, we cannot simply
migrate. Types from the proto package are exposed to users of packages
in this repo. If we migrate here, users have to migrate to. Thus, we
could only migrate with a major version bump.
In different news, with all the inline lint:ignore comments, including
the existing ones, there is no need to repeat the exception in the
Makefile.
A current version of `staticcheck` is happy with the code after this
commit. golangci-lint is broken at the moment, however, and ignores
the lint:ignore comments in the code as well as those via envvar.
Signed-off-by: beorn7 <beorn@grafana.com>
This is, sadly, the only way to avoid a breaking change. The cost is
that anyone using exemplars has to perform a type assertion. This is,
however, a common pattern where interfaces turn out to need additional
methods in a stable library or only some implementations can provide
the additional methods (AKA "interface upgrade").
Needless to say that in v2 of this library, we'll do things in a more
straight forward way.
Signed-off-by: beorn7 <beorn@grafana.com>
This is in line with
https://prometheus.io/docs/instrumenting/writing_clientlibs/#metric-description-and-help
Since the zero value of a string in Go is `""`, we cannot distinguish
between a Help string not set and an empty Help string. Thus, we just
make it formally optional here with an encouragement to set it in the
doc comment.
In v0.10, the Help string will probably become a "normal" argument of
the constructor rather than a field in an Opts struct.
Signed-off-by: beorn7 <beorn@soundcloud.com>
The idea behind it is described in detail in
https://github.com/prometheus/client_golang/issues/320 .
This commit also updates the example given in
promhttp/instrument_server_test.go , which nicely illustrates the
benefit of this change.
So far, currying could be emulated by creating different metric vec's
with different values in their ConstLabels. This was quite difficult
to grasp - which is essentially what was done in the example mentioned
above. Now that this use case can be solved without ConstLabels, we
can safely declare ConstLabels as rarely used. (Perhaps we can
deprecate them entirely one day, but I'll take a raincheck on that
when the changes of v0.10 have materialized.) This commit thus also
updates the ConstLabel doc comments in the various Opts. (It contained
fairly outdated stuff anyway.)
The "panic in case of error" code was so far in metricVec. This pulls
it up into the exported types like CounterVec. This is code
replication, but it avoids an explicit type conversion. Mostly,
however, this is preparation to make the wrapped metricVec an
interface (required for curried vec's).
This is in preparation for "curried" metric vecs, as discussed.
And it's a good thing anyway. The exported MetricVec was from a time
when I thought people would define own Metric types and then create
Vecs of it. That has never happened.
The new vendoring was produced by running:
godep save -r ./examples/... ./prometheus/... ./text/... ./model/... ./extraction/...
Two things to note:
- "extraction/processor0_0_{1,2}_test.go" imported a package from
"github.com/prometheus/prometheus", all for just one tiny testing
function. To not have to deal with a circular vendoring dependency, I
simply replaced the usage of the function by some in-line logic.
- godep grouped the rewritten imports slightly differently for some
reason, but at least the standard library imports are still in a
separate section. Not sure if it's worth manually keeping our old
import grouping scheme or if we should simply use that godep-generated
one.
beorn7