go: cmd/go: get panics with "can't find reason for requirement on"

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

$ go version
go version go1.17 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

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

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/mikhail/Library/Caches/go-build"
GOENV="/Users/mikhail/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/mikhail/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/mikhail/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/opt/go/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/opt/go/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.6"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/mikhail/src/gitlab-agent/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 -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/f5/v0r6vhks50d61jjmrhfgnlbh0000gn/T/go-build1390498625=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I’m trying new pruned modules functionality to see if it helps reduce the number of tracked dependencies in my project.

• I’ve changed one of the libraries to go 1.17 and ran go1.17 mod tidy -compat=1.17. I had to change the go directive in go.mod to 1.17 manually, re-run the command, and only then it worked - is this expected? Pushed this into a branch (commit).
• Then in my project I did the same as above, and then ran:

go1.17 get gitlab.com/gitlab-org/labkit@fc0c07abad6a32b5b77e16289fcc72d38f8411ab
go: downloading gitlab.com/gitlab-org/labkit v1.9.1-0.20210826103322-fc0c07abad6a
panic: internal error: can't find reason for requirement on github.com/google/gofuzz@v1.1.0

goroutine 1 [running]:
cmd/go/internal/modget.(*resolver).updateBuildList.func1({{0xc000ac4a68, 0xc00065d920}, {0xc00002afd0, 0xc000010570}})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1794 +0x10a
cmd/go/internal/modget.(*resolver).updateBuildList(0xc0005cc100, {0x166fac0, 0xc00002a0c0}, {0x0, 0x0, 0x0})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1799 +0x5bb
cmd/go/internal/modget.(*resolver).resolveQueries(0xc0005cc100, {0x166fac0, 0xc00002a0c0}, {0xc000010050, 0x1, 0x1ac4658})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1278 +0x1e5
cmd/go/internal/modget.runGet({0x166fac0, 0xc00002a0c0}, 0xc000026318, {0xc0000201d0, 0x1, 0x1})
        /usr/local/go/src/cmd/go/internal/modget/get.go:300 +0x374
main.invoke(0x1983c80, {0xc0000201c0, 0x2, 0x2})
        /usr/local/go/src/cmd/go/main.go:216 +0x2f6
main.main()
        /usr/local/go/src/cmd/go/main.go:173 +0x78e

• Then I thought “It shouldn’t crash, but maybe I’ve messed something up in the library repo?”. I went there, ran go1.17 mod tidy (without -compat=1.17) and indeed there was a new change (commit). I pushed it too.
• Ran go get in my project:

go1.17 get gitlab.com/gitlab-org/labkit@c3248dffceabec66f9f26a08feb847a438d33707
go: downloading gitlab.com/gitlab-org/labkit v1.9.1-0.20210826104146-c3248dffceab
panic: internal error: can't find reason for requirement on github.com/google/gofuzz@v1.1.0

goroutine 1 [running]:
cmd/go/internal/modget.(*resolver).updateBuildList.func1({{0xc0004c74d0, 0xc00073ed20}, {0xc00002afd6, 0xc000604090}})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1794 +0x10a
cmd/go/internal/modget.(*resolver).updateBuildList(0xc00059a100, {0x166fac0, 0xc00002a0c0}, {0x0, 0x0, 0x0})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1799 +0x5bb
cmd/go/internal/modget.(*resolver).resolveQueries(0xc00059a100, {0x166fac0, 0xc00002a0c0}, {0xc000010050, 0x1, 0x1ac4658})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1278 +0x1e5
cmd/go/internal/modget.runGet({0x166fac0, 0xc00002a0c0}, 0xc000026318, {0xc0000201d0, 0x1, 0x1})
        /usr/local/go/src/cmd/go/internal/modget/get.go:300 +0x374
main.invoke(0x1983c80, {0xc0000201c0, 0x2, 0x2})
        /usr/local/go/src/cmd/go/main.go:216 +0x2f6
main.main()
        /usr/local/go/src/cmd/go/main.go:173 +0x78e

The second time it actually was not crashing immediately but after a few seconds (looks like it downloaded the library this time) it still did.

Here is the commit in my project, on which I’m trying to run the above commands and it crashes.

What did you expect to see?

No crashes. If something is wrong with my modules or their dependencies, a comprehensible error.

What did you see instead?

See above.