dep init: pkgtree poisonblack panic due to nil map entry

Go Version 1.8.1

Architecture Darwin x86_64 (Sierra 10.12.4)

I can consistently reproduce this on https://github.com/uber-go/zap@fab453050a7a08c35f31fc5fff6f2dbd962285ab (tip of master at the time of writing):

Running dep init with the latest master of dep (8bdd9e5cb8e331a8fb505d9c4f62bd58bbac40b3)

zap - master! ❯ dep init -v
dep: Finding dependencies for "github.com/uber-go/zap"...
dep: Found 193 dependencies.
Searching GOPATH for projects...
dep: Building dependency graph...
dep: Found import of "github.com/Sirupsen/logrus", analyzing...
  Using ^0.8.7 as constraint for direct dep github.com/Sirupsen/logrus
  Locking in v0.8.7 (418b41d) for direct dep github.com/Sirupsen/logrus
dep: Found import of "github.com/VividCortex/gohistogram", analyzing...
dep: Could not determine version for "github.com/VividCortex/gohistogram", omitting from generated manifest
dep: Found import of "github.com/afex/hystrix-go/hystrix", analyzing...
dep: Could not determine version for "github.com/afex/hystrix-go", omitting from generated manifest
dep: Found import of "github.com/apache/thrift/lib/go/thrift", analyzing...
  Using cada370 as hint for direct dep github.com/apache/thrift
dep: Found import of "github.com/apex/log", analyzing...
dep: Could not determine version for "github.com/apex/log", omitting from generated manifest
dep: Found import of "github.com/aphistic/golf", analyzing...
dep: Could not determine version for "github.com/aphistic/golf", omitting from generated manifest
dep: Found import of "github.com/aws/aws-sdk-go/aws", analyzing...
  Using master as constraint for direct dep github.com/aws/aws-sdk-go
  Locking in master (64ecfaa) for direct dep github.com/aws/aws-sdk-go
dep: Found import of "github.com/bugsnag/bugsnag-go", analyzing...
dep: Could not determine version for "github.com/bugsnag/bugsnag-go", omitting from generated manifest
dep: Found import of "github.com/cactus/go-statsd-client/statsd", analyzing...
  Using dc93b85 as hint for direct dep github.com/cactus/go-statsd-client
dep: Found import of "github.com/coreos/etcd/client", analyzing...
  Using master as constraint for direct dep github.com/coreos/etcd
  Locking in master (f2a4993) for direct dep github.com/coreos/etcd
dep: Found import of "github.com/davecgh/go-spew/spew", analyzing...
  Using 5215b55 as hint for direct dep github.com/davecgh/go-spew
dep: Found import of "github.com/dgrijalva/jwt-go", analyzing...
dep: Could not determine version for "github.com/dgrijalva/jwt-go", omitting from generated manifest
dep: Found import of "github.com/getsentry/raven-go", analyzing...
  Using c8f8fb7 as hint for direct dep github.com/getsentry/raven-go
dep: Found import of "github.com/go-kit/kit/circuitbreaker", analyzing...
dep: Could not determine version for "github.com/go-kit/kit", omitting from generated manifest
dep: Found import of "github.com/go-logfmt/logfmt", analyzing...
dep: Could not determine version for "github.com/go-logfmt/logfmt", omitting from generated manifest
dep: Found import of "github.com/go-stack/stack", analyzing...
  Using master as constraint for direct dep github.com/go-stack/stack
  Locking in master (100eb0c) for direct dep github.com/go-stack/stack
dep: Found import of "github.com/golang/protobuf/proto", analyzing...
  Using 8df8a93 as hint for direct dep github.com/golang/protobuf
dep: Found import of "github.com/gorilla/mux", analyzing...
  Using master as constraint for direct dep github.com/gorilla/mux
  Locking in master (c9e326e) for direct dep github.com/gorilla/mux
dep: Found import of "github.com/hashicorp/consul/api", analyzing...
  Using master as constraint for direct dep github.com/hashicorp/consul
  Locking in master (71e3901) for direct dep github.com/hashicorp/consul
dep: Found import of "github.com/influxdata/influxdb/client/v2", analyzing...
dep: Could not determine version for "github.com/influxdata/influxdb", omitting from generated manifest
dep: Found import of "github.com/jessevdk/go-flags", analyzing...
  Using master as constraint for direct dep github.com/jessevdk/go-flags
  Locking in master (460c7bb) for direct dep github.com/jessevdk/go-flags
dep: Found import of "github.com/juju/ratelimit", analyzing...
dep: Could not determine version for "github.com/juju/ratelimit", omitting from generated manifest
dep: Found import of "github.com/kr/logfmt", analyzing...
dep: Could not determine version for "github.com/kr/logfmt", omitting from generated manifest
dep: Found import of "github.com/lightstep/lightstep-tracer-go", analyzing...
dep: Could not determine version for "github.com/lightstep/lightstep-tracer-go", omitting from generated manifest
dep: Found import of "github.com/mattn/go-colorable", analyzing...
  Using master as constraint for direct dep github.com/mattn/go-colorable
  Locking in master (d228849) for direct dep github.com/mattn/go-colorable
dep: Found import of "github.com/mattn/go-isatty", analyzing...
  Using master as constraint for direct dep github.com/mattn/go-isatty
  Locking in master (30a891c) for direct dep github.com/mattn/go-isatty
dep: Found import of "github.com/opentracing/opentracing-go", analyzing...
  Using 1b62b0c as hint for direct dep github.com/opentracing/opentracing-go
dep: Found import of "github.com/openzipkin/zipkin-go-opentracing", analyzing...
dep: Could not determine version for "github.com/openzipkin/zipkin-go-opentracing", omitting from generated manifest
dep: Found import of "github.com/pborman/uuid", analyzing...
  Using cccd189 as hint for direct dep github.com/pborman/uuid
dep: Found import of "github.com/performancecopilot/speed", analyzing...
dep: Could not determine version for "github.com/performancecopilot/speed", omitting from generated manifest
dep: Found import of "github.com/pkg/errors", analyzing...
  Using master as constraint for direct dep github.com/pkg/errors
  Locking in master (ff09b13) for direct dep github.com/pkg/errors
dep: Found import of "github.com/pmezard/go-difflib/difflib", analyzing...
  Using e8554b8 as hint for direct dep github.com/pmezard/go-difflib
dep: Found import of "github.com/prometheus/client_golang/prometheus", analyzing...
dep: Could not determine version for "github.com/prometheus/client_golang", omitting from generated manifest
dep: Found import of "github.com/rogpeppe/fastuuid", analyzing...
dep: Could not determine version for "github.com/rogpeppe/fastuuid", omitting from generated manifest
dep: Found import of "github.com/samuel/go-zookeeper/zk", analyzing...
dep: Could not determine version for "github.com/samuel/go-zookeeper", omitting from generated manifest
dep: Found import of "github.com/sirupsen/logrus", analyzing...
  Using ^0.8.7 as constraint for direct dep github.com/sirupsen/logrus
  Locking in v0.8.7 (418b41d) for direct dep github.com/sirupsen/logrus
dep: Found import of "github.com/sony/gobreaker", analyzing...
dep: Could not determine version for "github.com/sony/gobreaker", omitting from generated manifest
dep: Found import of "github.com/streadway/handy/breaker", analyzing...
dep: Could not determine version for "github.com/streadway/handy", omitting from generated manifest
dep: Found import of "github.com/stretchr/objx", analyzing...
  Using 1a9d0bb as hint for direct dep github.com/stretchr/objx
dep: Found import of "github.com/stretchr/testify/assert", analyzing...
  Using e3a8ff8 as hint for direct dep github.com/stretchr/testify
dep: Found import of "github.com/stvp/go-udp-testing", analyzing...
dep: Could not determine version for "github.com/stvp/go-udp-testing", omitting from generated manifest
dep: Found import of "github.com/tj/go-elastic/batch", analyzing...
dep: Could not determine version for "github.com/tj/go-elastic", omitting from generated manifest
dep: Found import of "github.com/tj/go-kinesis", analyzing...
dep: Could not determine version for "github.com/tj/go-kinesis", omitting from generated manifest
dep: Found import of "github.com/tobi/airbrake-go", analyzing...
dep: Could not determine version for "github.com/tobi/airbrake-go", omitting from generated manifest
dep: Found import of "github.com/uber/bark", analyzing...
dep: Could not determine version for "github.com/uber/bark", omitting from generated manifest
dep: Found import of "go.pedge.io/lion", analyzing...
dep: Could not determine version for "go.pedge.io/lion", omitting from generated manifest
dep: Found import of "go.uber.org/atomic", analyzing...
  Using master as constraint for direct dep go.uber.org/atomic
  Locking in master (4e33664) for direct dep go.uber.org/atomic
dep: Found import of "go.uber.org/zap", analyzing...
  Using master as constraint for direct dep go.uber.org/zap
  Locking in master (1550bc0) for direct dep go.uber.org/zap
dep: Found import of "golang.org/x/net/context", analyzing...
  Using 7f88271 as hint for direct dep golang.org/x/net
dep: Found import of "golang.org/x/sys/plan9", analyzing...
  Using master as constraint for direct dep golang.org/x/sys
  Locking in master (a646d33) for direct dep golang.org/x/sys
dep: Found import of "google.golang.org/grpc", analyzing...
dep: Could not determine version for "google.golang.org/grpc", omitting from generated manifest
dep: Found import of "gopkg.in/inconshreveable/log15.v2", analyzing...
dep: Could not determine version for "gopkg.in/inconshreveable/log15.v2", omitting from generated manifest
dep: Found import of "sourcegraph.com/sourcegraph/appdash", analyzing...
dep: Could not determine version for "sourcegraph.com/sourcegraph/appdash", omitting from generated manifest
dep: Analyzing transitive imports...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc/thrift/gen-go/addsvc"...
dep: Analyzing "github.com/go-kit/kit/metrics/expvar"...
dep: Analyzing "github.com/hashicorp/consul/api"...
dep: Analyzing "github.com/hashicorp/go-cleanhttp"...
  Locking in master (ce617e7) for transitive dep github.com/hashicorp/go-cleanhttp
dep: Analyzing "github.com/hashicorp/serf/coordinate"...
  Locking in master (39c7c06) for transitive dep github.com/hashicorp/serf
dep: Analyzing "github.com/influxdata/influxdb/client/v2"...
dep: Analyzing "gopkg.in/inconshreveable/log15.v2"...
dep: Analyzing "github.com/bugsnag/bugsnag-go"...
dep: Analyzing "github.com/go-kit/kit/log/term"...
dep: Analyzing "github.com/go-kit/kit/metrics/dogstatsd"...
dep: Analyzing "github.com/opentracing/opentracing-go/mocktracer"...
dep: Analyzing "github.com/tj/go-elastic/batch"...
dep: Analyzing "go.uber.org/zap"...
dep: Analyzing "go.uber.org/atomic"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/booking"...
dep: Analyzing "github.com/stretchr/testify/assert"...
dep: Analyzing "github.com/davecgh/go-spew/spew"...
dep: Analyzing "github.com/pmezard/go-difflib/difflib"...
dep: Analyzing "go.uber.org/zap/internal/color"...
dep: Analyzing "go.uber.org/zap/internal/multierror"...
dep: Analyzing "github.com/davecgh/go-spew/spew/testdata"...
dep: Analyzing "github.com/getsentry/raven-go"...
dep: Analyzing "github.com/go-kit/kit/metrics/influx"...
dep: Analyzing "github.com/go-kit/kit/sd"...
dep: Analyzing "github.com/go-kit/kit/transport/grpc"...
dep: Analyzing "github.com/stvp/go-udp-testing"...
dep: Analyzing "github.com/Sirupsen/logrus/hooks/airbrake"...
dep: Analyzing "github.com/tobi/airbrake-go"...
dep: Analyzing "github.com/juju/ratelimit"...
dep: Analyzing "github.com/pborman/uuid"...
dep: Analyzing "sourcegraph.com/sourcegraph/appdash/opentracing"...
dep: Analyzing "github.com/coreos/etcd/client"...
dep: Analyzing "github.com/go-kit/kit/examples/profilesvc"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/handling"...
dep: Analyzing "github.com/go-kit/kit/sd/lb"...
dep: Analyzing "github.com/opentracing/opentracing-go"...
dep: Analyzing "gopkg.in/inconshreveable/log15.v2/term"...
dep: Analyzing "github.com/aws/aws-sdk-go/aws"...
dep: Analyzing "github.com/go-ini/ini"...
  Locking in master (afbd495) for transitive dep github.com/go-ini/ini
dep: Analyzing "github.com/go-kit/kit/examples/shipping/voyage"...
dep: Analyzing "github.com/go-kit/kit/log/level"...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc/client/thrift"...
dep: Analyzing "github.com/go-kit/kit/transport/httprp"...
dep: Analyzing "github.com/uber/bark/mocks"...
dep: Analyzing "go.uber.org/zap/zaptest/observer"...
dep: Analyzing "gopkg.in/inconshreveable/log15.v2/stack"...
dep: Analyzing "golang.org/x/sys/unix"...
dep: Analyzing "golang.org/x/sys/windows"...
dep: Analyzing "github.com/VividCortex/gohistogram"...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc/client/http"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/tracking"...
dep: Analyzing "github.com/go-kit/kit/metrics/teststat"...
dep: Analyzing "github.com/go-kit/kit/util/conn"...
dep: Analyzing "golang.org/x/net/context"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/inspection"...
dep: Analyzing "github.com/go-kit/kit/ratelimit"...
dep: Analyzing "github.com/go-stack/stack"...
dep: Analyzing "github.com/performancecopilot/speed"...
dep: Analyzing "go.uber.org/zap/internal/bufferpool"...
dep: Analyzing "golang.org/x/sys/windows/registry"...
dep: Analyzing "github.com/apex/log/handlers/text"...
dep: Analyzing "github.com/go-kit/kit/tracing/opentracing"...
dep: Analyzing "github.com/golang/protobuf/proto"...
dep: Analyzing "github.com/lightstep/lightstep-tracer-go"...
dep: Analyzing "github.com/pkg/errors"...
dep: Analyzing "github.com/apex/log/handlers/discard"...
dep: Analyzing "github.com/go-kit/kit/metrics/discard"...
dep: Analyzing "github.com/samuel/go-zookeeper/zk"...
dep: Analyzing "golang.org/x/sys/windows/svc/mgr"...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc/pb"...
dep: Analyzing "github.com/jessevdk/go-flags"...
dep: Analyzing "github.com/stretchr/objx"...
dep: Analyzing "go.pedge.io/lion"...
dep: Analyzing "github.com/go-kit/kit/transport/grpc/_grpc_test/pb"...
dep: Analyzing "github.com/stretchr/testify/http"...
dep: Analyzing "golang.org/x/sys/windows/svc/eventlog"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/cargo"...
dep: Analyzing "github.com/sirupsen/logrus"...
dep: Analyzing "github.com/tj/go-kinesis"...
dep: Analyzing "golang.org/x/sys/windows/svc"...
dep: Analyzing "github.com/aws/aws-sdk-go/service/kinesis"...
dep: Analyzing "github.com/jmespath/go-jmespath"...
  Locking in master (c01cf91) for transitive dep github.com/jmespath/go-jmespath
dep: Analyzing "github.com/go-kit/kit/examples/shipping/routing"...
dep: Analyzing "github.com/stretchr/testify/mock"...
dep: Analyzing "github.com/go-kit/kit/metrics/internal/lv"...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc"...
dep: Analyzing "github.com/go-kit/kit/metrics/graphite"...
dep: Analyzing "github.com/go-kit/kit/metrics/statsd"...
dep: Analyzing "github.com/rogpeppe/fastuuid"...
dep: Analyzing "github.com/stretchr/testify/require"...
dep: Analyzing "go.uber.org/zap/internal/exit"...
dep: Analyzing "github.com/Sirupsen/logrus"...
dep: Analyzing "github.com/apex/log"...
dep: Analyzing "github.com/apex/log/handlers/memory"...
dep: Analyzing "github.com/cactus/go-statsd-client/statsd"...
dep: Analyzing "github.com/go-kit/kit/log/deprecated_levels"...
dep: Analyzing "github.com/streadway/handy/breaker"...
dep: Analyzing "github.com/go-kit/kit/sd/consul"...
dep: Analyzing "github.com/sony/gobreaker"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/inmem"...
dep: Analyzing "github.com/uber/bark"...
dep: Analyzing "github.com/apex/log/handlers/json"...
dep: Analyzing "github.com/gorilla/mux"...
dep: Analyzing "github.com/gorilla/context"...
  Locking in master (1ea2538) for transitive dep github.com/gorilla/context
dep: Analyzing "google.golang.org/grpc/metadata"...
dep: Analyzing "github.com/apex/log/handlers/logfmt"...
dep: Analyzing "github.com/dgrijalva/jwt-go"...
dep: Analyzing "github.com/prometheus/client_golang/prometheus"...
dep: Analyzing "go.uber.org/zap/buffer"...
dep: Analyzing "github.com/afex/hystrix-go/hystrix"...
dep: Analyzing "github.com/go-kit/kit/examples/shipping/location"...
dep: Analyzing "github.com/go-kit/kit/metrics/generic"...
dep: Analyzing "github.com/go-kit/kit/metrics/prometheus"...
dep: Analyzing "github.com/opentracing/opentracing-go/ext"...
dep: Analyzing "go.uber.org/zap/zapcore"...
dep: Analyzing "github.com/aphistic/golf"...
dep: Analyzing "github.com/go-kit/kit/sd/cache"...
dep: Analyzing "github.com/go-kit/kit/transport/http"...
dep: Analyzing "github.com/mattn/go-isatty"...
dep: Analyzing "github.com/aws/aws-sdk-go/aws/session"...
dep: Analyzing "go.uber.org/zap/zaptest"...
dep: Analyzing "github.com/apex/log/handlers/multi"...
dep: Analyzing "github.com/go-kit/kit/metrics"...
dep: Analyzing "github.com/kr/logfmt"...
dep: Analyzing "github.com/mattn/go-colorable"...
dep: Analyzing "golang.org/x/net/context/ctxhttp"...
dep: Analyzing "github.com/apex/log/handlers/level"...
dep: Analyzing "github.com/go-kit/kit/examples/addsvc/client/grpc"...
dep: Analyzing "github.com/go-kit/kit/log"...
dep: Analyzing "github.com/go-kit/kit/transport/grpc/_grpc_test"...
dep: Analyzing "golang.org/x/sys/windows/svc/debug"...
dep: Analyzing "sourcegraph.com/sourcegraph/appdash"...
dep: Analyzing "github.com/go-kit/kit/endpoint"...
dep: Analyzing "github.com/go-kit/kit/metrics/internal/ratemap"...
dep: Analyzing "github.com/openzipkin/zipkin-go-opentracing"...
dep: Analyzing "golang.org/x/sys/plan9"...
dep: Analyzing "google.golang.org/grpc"...
dep: Analyzing "github.com/apache/thrift/lib/go/thrift"...
dep: Analyzing "github.com/go-kit/kit/circuitbreaker"...
dep: Analyzing "github.com/go-logfmt/logfmt"...
Using network for remaining projects...
dep: Solving...
Root project is "github.com/uber-go/zap"
 146 transitively valid internal packages
 135 external packages imported from 53 projects
(0)   ✓ select (root)
(1)     ? attempt github.com/Sirupsen/logrus with 2 pkgs; at least 1 versions to try
(1)         try github.com/Sirupsen/logrus@v0.8.7
(1)     ✓ select github.com/Sirupsen/logrus@v0.8.7 w/2 pkgs
(2)     ? attempt github.com/aws/aws-sdk-go with 3 pkgs; at least 1 versions to try
(2)         try github.com/aws/aws-sdk-go@master
(2)     ✓ select github.com/aws/aws-sdk-go@master w/19 pkgs
(3)     ? attempt github.com/apache/thrift with 1 pkgs; at least 1 versions to try
(3)         try github.com/apache/thrift@cada37008ce6e609fe6312596d3ced760e5cd60c
(3)     ✓ select github.com/apache/thrift@cada37008ce6e609fe6312596d3ced760e5cd60c w/1 pkgs
(4)     ? attempt github.com/cactus/go-statsd-client with 1 pkgs; at least 1 versions to try
(4)         try github.com/cactus/go-statsd-client@dc93b8587d799a204e96175505fff9678a8ec3e1
(4)     ✓ select github.com/cactus/go-statsd-client@dc93b8587d799a204e96175505fff9678a8ec3e1 w/1 pkgs
(5)     ? attempt github.com/go-ini/ini with 1 pkgs; at least 1 versions to try
(5)         try github.com/go-ini/ini@master
(5)     ✓ select github.com/go-ini/ini@master w/1 pkgs
(6)     ? attempt github.com/coreos/etcd with 1 pkgs; at least 1 versions to try
(6)         try github.com/coreos/etcd@master
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x114d608]

goroutine 1 [running]:
github.com/golang/dep/internal/gps/pkgtree.wmToReach.func3(0xc42044a1c0, 0x1, 0x1, 0xc42027b9a1, 0x4b)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:632 +0x78
github.com/golang/dep/internal/gps/pkgtree.wmToReach.func4(0xc42027b9a1, 0x4b, 0xc42044a1c0, 0x1, 0x1, 0xc42044a101)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:771 +0x462
github.com/golang/dep/internal/gps/pkgtree.wmToReach.func4(0xc4207f8f30, 0x21, 0xc42044a1c0, 0x1, 0x1, 0x0)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:728 +0xd08
github.com/golang/dep/internal/gps/pkgtree.wmToReach(0xc4207cbd20, 0xc4207cbd01, 0xc4207cbd10, 0xc4208278d8)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:810 +0xd1c
github.com/golang/dep/internal/gps/pkgtree.PackageTree.ToReachMap(0xc4201f93a0, 0x16, 0xc420994840, 0x10001, 0xc4209871d0, 0x167f520, 0xc4202f0de0)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:501 +0x2c0
github.com/golang/dep/internal/gps.(*solver).getImportsAndConstraintsOf(0xc42001efc0, 0xc4201f93a0, 0x16, 0x0, 0x0, 0x167f520, 0xc4202f0de0, 0xc4203107f0, 0x1, 0x1, ...)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/solver.go:537 +0x1f7
github.com/golang/dep/internal/gps.(*solver).check(0xc42001efc0, 0xc4201f93a0, 0x16, 0x0, 0x0, 0x167f520, 0xc4202f0de0, 0xc4203107f0, 0x1, 0x1, ...)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/satisfy.go:43 +0x1f0
github.com/golang/dep/internal/gps.(*solver).findValidVersion(0xc42001efc0, 0xc420253900, 0xc4203107f0, 0x1, 0x1, 0x0, 0xc4203107f0)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/solver.go:807 +0x2d5
github.com/golang/dep/internal/gps.(*solver).createVersionQueue(0xc42001efc0, 0xc4201f93a0, 0x16, 0x0, 0x0, 0xc4203107f0, 0x1, 0x1, 0x0, 0x0, ...)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/solver.go:780 +0xafc
github.com/golang/dep/internal/gps.(*solver).solve(0xc42001efc0, 0x0, 0x0, 0x1e)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/solver.go:397 +0x471
github.com/golang/dep/internal/gps.(*solver).Solve(0xc42001efc0, 0x2e, 0x167b220, 0x16c8dc8, 0xc42001c09c)
        /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/solver.go:348 +0xab
main.(*initCommand).Run(0xc420153732, 0xc420137840, 0xc420010320, 0x0, 0x0, 0x0, 0x0)
        /Users/aiden/src/go/src/github.com/golang/dep/cmd/dep/init.go:182 +0xf17
main.(*Config).Run(0xc42001af60, 0xc42001af60)
        /Users/aiden/src/go/src/github.com/golang/dep/cmd/dep/main.go:159 +0x8b3
main.main()
        /Users/aiden/src/go/src/github.com/golang/dep/cmd/dep/main.go:44 +0x253

Diving into variables with delve:

> github.com/golang/dep/internal/gps/pkgtree.wmToReach.func3() /Users/aiden/src/go/src/github.com/golang/dep/internal/gps/pkgtree/pkgtree.go:629 (hits goroutine(1):1 total:1) (PC: 0x114fd04)
   624:         poisonBlack := func(path []string, from string) {
   625:                 // Because the outer dfe loop ensures we never directly re-visit a pkg
   626:                 // that was already completed (black), we don't have to defend against
   627:                 // an empty path here.
   628:
=> 629:                 fromErr := errmap[from]
   630:                 err := &ProblemImportError{
   631:                         Err:   fromErr.Err,
   632:                         Cause: make([]string, 0, len(path)+len(fromErr.Cause)+1),
   633:                 }
   634:                 err.Cause = append(err.Cause, path...)
(dlv) p path
[]string len: 1, cap: 1, [
        "github.com/coreos/etcd/etcdserver/auth",
]
(dlv) p from
"github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/p...+11 more"
(dlv) locals
poison = github.com/golang/dep/internal/gps/pkgtree.wmToReach.func1
fromErr = (*github.com/golang/dep/internal/gps/pkgtree.ProblemImportError)(0x1011acc)
errmap = map[string]*github.com/golang/dep/internal/gps/pkgtree.ProblemImportError [...]
err = (*github.com/golang/dep/internal/gps/pkgtree.ProblemImportError)(0xc420607b40)
(dlv) p errmap
map[string]*github.com/golang/dep/internal/gps/pkgtree.ProblemImportError [
        "github.com/coreos/etcd/snap/snappb": *{
                ImportPath: "github.com/coreos/etcd/snap/snappb",
                Cause: []string len: 1, cap: 1, [
                        "github.com/coreos/etcd/Godeps/_workspace/src/github.com/gogo/pro...+11 more",
                ],
                Err: error(*errors.errorString) ...,},
        "github.com/coreos/etcd/hack/insta-discovery": *{
                ImportPath: "github.com/coreos/etcd/hack/insta-discovery",
                Cause: []string len: 0, cap: 0, [],
                Err: error(*go/build.NoGoError) ...,},
        "github.com/coreos/etcd/hack/tls-setup/config": *{
                ImportPath: "github.com/coreos/etcd/hack/tls-setup/config",
                Cause: []string len: 0, cap: 0, [],
                Err: error(*go/build.NoGoError) ...,},
        "github.com/coreos/etcd/hack": *{
                ImportPath: "github.com/coreos/etcd/hack",
                Cause: []string len: 0, cap: 0, [],
                Err: error(*go/build.NoGoError) ...,},
        "github.com/coreos/etcd/version": *{
                ImportPath: "github.com/coreos/etcd/version",
                Cause: []string len: 2, cap: 2, [
                        "github.com/coreos/etcd/pkg/fileutil",
                        "github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/p...+11 more",
                ],
                Err: error(*errors.errorString) ...,},
        "github.com/coreos/etcd/pkg/fileutil": *{
                ImportPath: "github.com/coreos/etcd/pkg/fileutil",
                Cause: []string len: 1, cap: 1, [
                        "github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/p...+11 more",
                ],
                Err: error(*errors.errorString) ...,},
]

basically, fromErr is nil and the comment above suggests that should never be the case.

It would be pretty easy to add a comma-ok and check for that, but I'm unfamiliar with this part of the codebase and don't want to band-aid if this is indicative of a larger issue. Looks like the code was originally added in 31795085c1afcd25d3c87e140f9d60b19e7684e7 but later moved.

golang / dep

dep init: pkgtree poisonblack panic due to nil map entry #617