cmd/go: "go mod tidy" removes an entry added to go.sum by "go build" for a replacement module

[misha-ridge]

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

1.11rc2

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/dottedmag/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/dottedmag/go"
GOPROXY=""
GORACE=""
GOROOT="/Users/dottedmag/kobold/deps/go1.11rc2.darwin-amd64/dist"
GOTMPDIR=""
GOTOOLDIR="/Users/dottedmag/kobold/deps/go1.11rc2.darwin-amd64/dist/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/dottedmag/tmp/foo/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/mt/1tmwnxv96cg2vl1nz74_c9cm0000gn/T/go-build168050972=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Added a replace directive for a module.

go build adds an entry for this replacement module to go.sum.
go mod tidy removes the entry from this replacement module.

Reproducer: https://github.com/misha-tectonic/go-mod-tidy-remove-replace-sum

Try go build ., see go.sum changed, then go mod tidy.

What did you expect to see?

go mod tidy does not remove entries added by go build .

What did you see instead?

go mod tidy removes entries added by go build ..

[ianlancetaylor]

CC @bcmills

[groob]

Seeing this in two separate projects that have a replace directive as well.

edit: running go mod tidy before a commit is an acceptable workaround for now.

[rsc]

Thanks for the repository for use in reproducing the problem. Even when you send such a repo, though, it is very helpful to also send a transcript with exact commands and outputs that you are seeing. It may well be that we run with a slightly different version of the tools or a different environment and don't get the same behavior, and we'd have no way of knowing. So please be more precise in the "what did you see" answer.

[myitcv]

This issue is probably related to/dup of #27868. There is a repro listed in #27868 (comment)

[misha-ridge]

Here you go:

% git diff
% go build .
% git diff
diff --git a/go.sum b/go.sum
index cd08da9..cad6fad 100644
--- a/go.sum
+++ b/go.sum
@@ -24,6 +24,7 @@ github.com/jmhodges/levigo v0.0.0-20161115193449-c42d9e0ca023 h1:y5P5G9cANJZt3MX
 github.com/jmhodges/levigo v0.0.0-20161115193449-c42d9e0ca023/go.mod h1:Q6Qx+uH3RAqyK4rFQroq9RL7mdkABMcfhEI+nNuzMJQ=
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515 h1:T+h1c/A9Gawja4Y9mFVWj2vyii2bbUNDw3kt9VxK2EY=
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFBFZlji/RkVcI2GknAs/DXo4wKdlNEc=
+github.com/misha-tectonic/iavl v0.9.3 h1:40j1x7QKAOXYqFm23l8cG/A0XvCqTPG/cemyRA6Ocec=
 github.com/misha-tectonic/iavl v0.9.3/go.mod h1:Tyg8i/tms/Cp33OZdedoyahF09y7l9wxHM2JC3m7Jbo=
 github.com/onsi/ginkgo v1.6.0 h1:Ix8l273rp3QzYgXSR+c8d1fTG7UPgYkOSELPhiY/YGw=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
% go mod tidy
% git diff
%

[myitcv]

I'm going to close this as a dup of #27868