I assume this was using a go at tip (near 1.18)?

I assume this was using a go at tip (near 1.18)?

Yes: go version devel go1.18-9ff0039848 Fri Jan 28 02:40:34 2022 +0000 linux/amd64

Reproduced:

~/x/tools$ go version
go version devel go1.18-c8b0dcea4a Wed Jan 26 20:51:54 2022 +0000 linux/amd64

~/x/tools$ git status
On branch issue50934-mod-download
nothing to commit, working tree clean

~/x/tools$ git rev-parse HEAD
461d130035e971840054f875ee8e9da69440af8f

~/x/tools$ go get -d golang.org/x/mod@master
go: upgraded golang.org/x/mod v0.5.1 => v0.6.0-dev.0.20220106191415-9b9b3d81d5e3

~/x/tools$ cd gopls

~/x/tools/gopls$ go test ./internal/regtest/workspace
go: golang.org/x/tools@v0.1.8 requires
        golang.org/x/mod@v0.6.0-dev.0.20220106191415-9b9b3d81d5e3: missing go.sum entry; to add it:
        go mod download golang.org/x/mod

~/x/tools/gopls$ go mod download -json golang.org/x/mod
{
        "Path": "golang.org/x/mod",
        "Version": "v0.5.1",
        "Info": "/usr/local/google/home/bcmills/pkg/mod/cache/download/golang.org/x/mod/@v/v0.5.1.info",
        "GoMod": "/usr/local/google/home/bcmills/pkg/mod/cache/download/golang.org/x/mod/@v/v0.5.1.mod",
        "Zip": "/usr/local/google/home/bcmills/pkg/mod/cache/download/golang.org/x/mod/@v/v0.5.1.zip",
        "Dir": "/usr/local/google/home/bcmills/pkg/mod/golang.org/x/mod@v0.5.1",
        "Sum": "h1:OJxoQ/rynoF0dcCdI7cLPktw/hR2cueqYfjm43oqK38=",
        "GoModSum": "h1:5OXOZSfqPIIbmVBIIKWRFfZjPR0E5r58TLhUjH0a2Ro="
}

This is kind of an edge-case interaction between replace, go mod download, and lazy module loading.

I think what's happening is:

• Because the version of golang.org/x/mod is listed explicitly in gopls/go.mod, go mod download believes that that version (v0.5.1) is accurate and does not load the full module graph.
• However, go test ./internal/regtest/workspace does load x/tools/go.mod, because it loads a package from x/tools and loading a package triggers a spot-check of the module's dependencies. That spot-check exposes two errors in the module graph: one is that the version of x/mod at the root of the graph is not the selected version, and the other is that some nodes in the module graph are missing checksums.
• Because we didn't successfully load the module dependencies, we reported the checksum error instead of the inconsistent-version error.

This will probably need a bit more thought to get right. Perhaps if we fail to load the module graph we should report any known version-inconsistencies before we report checksum errors.

I ran into something that looks like the same issue in franz-go today.

franz-go % cd examples/bench
bench % go build
go: github.com/twmb/franz-go@v1.5.3 requires
	github.com/klauspost/compress@v1.15.9: missing go.sum entry; to add it:
	go mod download github.com/klauspost/compress
bench % go mod download github.com/klauspost/compress
bench % go build
go: github.com/twmb/franz-go@v1.5.3 requires
	github.com/klauspost/compress@v1.15.9: missing go.sum entry; to add it:
	go mod download github.com/klauspost/compress

Running go mod tidy resolved it, with this diff to the go.sum:

-github.com/klauspost/compress v1.15.6 h1:6D9PcO8QWu0JyaQ2zUMmu16T1T+zjjEpP91guRsvDfY=
-github.com/klauspost/compress v1.15.6/go.mod h1:PhcZ0MbTNciWF3rruxRgKxI5NkcHHrHUDtV4Yw2GlzU=
+github.com/klauspost/compress v1.15.9 h1:wKRjX6JRtDdrE9qwa4b/Cip7ACOshUI4smpCQanqjSY=
+github.com/klauspost/compress v1.15.9/go.mod h1:PhcZ0MbTNciWF3rruxRgKxI5NkcHHrHUDtV4Yw2GlzU=

Would be great to see this fixed - it was very confusing!

I was having the same problem. Using goimports returns:

../pkg/mod/golang.org/x/tools@v0.9.1/internal/gocommand/vendor.go:17:2: golang.org/x/mod@v0.10.0: missing go.sum entry for go.mod file; to add it:
        go mod download golang.org/x/mod
../pkg/mod/golang.org/x/tools@v0.9.1/internal/imports/mod.go:21:2: golang.org/x/mod@v0.10.0: missing go.sum entry for go.mod file; to add it:
        go mod download golang.org/x/mod

And it would add golang.org/x/mod v0.10.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs= to go.sum
Then, when I do go mod tidy, the change in go.sum is gone. So this become a loop..

I was having the same problem. Using goimports returns:

../pkg/mod/golang.org/x/tools@v0.9.1/internal/gocommand/vendor.go:17:2: golang.org/x/mod@v0.10.0: missing go.sum entry for go.mod file; to add it:
        go mod download golang.org/x/mod
../pkg/mod/golang.org/x/tools@v0.9.1/internal/imports/mod.go:21:2: golang.org/x/mod@v0.10.0: missing go.sum entry for go.mod file; to add it:
        go mod download golang.org/x/mod

And it would add golang.org/x/mod v0.10.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs= to go.sum Then, when I do go mod tidy, the change in go.sum is gone. So this become a loop..

I solved this problem by go get golang.org/x/mod. And it download a latest version in go.mod and go.sum.
Well it did help me but the way is to introduce a new version of package. Stiil confused why go mod tidy would remove a go.sum entry that goimports required