x/tools/benchmark: support parsing custom metrics

[jsternberg]

What version of Go are you using (go version)?

$ go version
go version go1.13 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN="/Users/jsternberg/go/pkg/bin/github.com/influxdata/flux"
GOCACHE="/Users/jsternberg/Library/Caches/go-build"
GOENV="/Users/jsternberg/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jsternberg/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.13/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.13/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jsternberg/go/src/github.com/influxdata/flux/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/w5/25fg3zv56y7cgd20q4fx_24m0000gn/T/go-build317574403=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I used ReportMetric when running a benchmark and attempted to use benchcmp to compare the benchmarks.

What did you expect to see?

I expected benchcmp to add an additional section showing the change in numbers for the custom benchmarks.

I then took a look at golang.org/x/tools/benchmark/parse to see if that functionality had been added or if the library had been updated so I could write the tool myself, but I see that the code there has not been updated to either read or expose the new custom metrics.

It would be very helpful to update this tool to support these custom metrics. We are beginning to use them to track other metrics and we would like to see how these other metrics change between two changesets.

What did you see instead?

Nothing.

[bcmills]

CC @ianthehat

[jsternberg]

If there's interest, I wrote some code to be able to accommodate my own personal need and it's in a fork at https://github.com/jsternberg/tools. I can clean it up and make it into a changeset if there is interest.