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

$ go version
go version go1.14.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/rravi/.cache/go-build"
GOENV="/home/rravi/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/rravi/.gotools"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build296868543=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. generate some traces with User Regions

$ go test cmd/trace -o trace.test
$ ./trace.test -savetraces
$ ls -l *.trace
-rw------- 1 rravi rravi 4459 Apr 19 01:29 TestAnalyzeAnnotationGC.trace
-rw------- 1 rravi rravi 2278 Apr 19 01:29 TestAnalyzeAnnotations.trace
-rw------- 1 rravi rravi 1938 Apr 19 01:29 TestAnalyzeAnnotationTaskTree.trace
-rw------- 1 rravi rravi 9967 Apr 19 01:29 TestDirectSemaphoreHandoff.trace
-rw------- 1 rravi rravi 1653 Apr 19 01:29 TestFoo.trace

2. start the trace tool

go tool trace ./TestAnalyzeAnnotations.trace
2020/04/19 01:34:02 Parsing trace...
2020/04/19 01:34:02 Splitting trace...
2020/04/19 01:34:02 Opening browser. Trace viewer is listening on http://127.0.0.1:45911

3. visit trace ui and click on "User-defined regions"
   
4. click on any of the links under the "Counts" column
   

What did you expect to see?

A table of user regions.

What did you see instead?

The table of user regions is missing.

Analysis

The root cause turned out to be a simple encoding error when forming the link: the pc URL parameter is encoded in base 10 whereas the handler expects it be encoded in base 16.

In a local branch, I have the above fix plus some UX improvements that I found useful since I use runtime/trace User Annotation API frequently to debug issues in production.

1. Links to pprof style graphs and download links for region specific io, block, syscall and scheduler profiles. I was surprised that this functionality was implemented on the server, but not easily discoverable via the UI.
   
2. Table headers get a cursor: pointer CSS style on hover to signal to the user that they're in fact clickable (for sorting).
   

I'll go through the Contribution Guide and put up a review soon.