cmd/go: 'go list -m all' fails when offline after 'go mod tidy' due to missing .info files

[jayconrod]

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

$ go version
go1.15.5

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=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jayconrod/Library/Caches/go-build"
GOENV="/Users/jayconrod/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jayconrod/Code/modcache"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jayconrod/go"
GOPRIVATE=""
GOPROXY="off"
GOROOT="/opt/go/installed"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/go/installed/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jayconrod/Code/test/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/rq/x0692kqj6ml8cvrhcqh5bswc008xj1/T/go-build494451782=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

go clean -modcache
go mod tidy
env GOPROXY=off
go list -m all

-- go.mod --
module m

go 1.15

require golang.org/x/mod v0.3.0
-- go.sum --
golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
golang.org/x/mod v0.3.0 h1:RM4zey1++hCTbCVQfnWeKs9/IEsaBLA8vTkd0WVtmH4=
golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-- use.go --
package use

import _ "golang.org/x/mod/semver"

What did you expect to see?

go list -m all should print all modules in build list.

What did you see instead?

go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off
go list -m: module lookup disabled by GOPROXY=off

go list -m loads an .info file for each module in the build list in order to include a timestamp in the output. Normally, the timestamp isn't shown, but it appears in the -json output, and it may appear in the -f output (related: #29666).

Most commands (including go mod tidy) don't download .info files for canonical versions. They're mainly used to resolve branch, tag, and commit names to versions. So when we go offline, the .info files are not in the cache, and go list -m fails.

We need to decide what to do here. If we can't load an .info file because we're offline or our proxies returned an error, we should just omit the field from the output instead of reporting an error.

We may want to reconsider reporting timestamps for canonical versions at all. I think the only case where we use them are when evaluating the @upgrade and @patch queries to decide whether a pseudo-version is chronologically newer than the highest release or pre-release version. Timestamps aren't required in the proxy protocol, and .info files aren't authenticated, so they can change and get out of sync with the cache.

cc @bcmills @matloob

[gopherbot]

Change https://golang.org/cl/271577 mentions this issue: cmd/go: remove ListModules call in runGet

[jayconrod]

After some discussion with @bcmills and @matloob yesterday, I we should stop reading .info files for canonical versions in go list -m and stop showing the Time field in go list -m -json.

The @upgrade and @patch queries use the timestamp if the current version is a pseudo-version to determine when the version returned by @latest is chronologically newer than the current version. The timestamp is part of the pseudo-version, but we retrieve and read .info files for non-pseudo-versions for this comparison.