travis: check for needed changes in go.mod and go.sum

.travis.yml

@@ -18,6 +18,7 @@ os:
 env:
  global:
   - GO111MODULE=on
+  - GOFLAGS="-mod=readonly"
  matrix:
   - TAGS=""
   - TAGS="-tags bounds"

.travis/script.d/check-generate.sh

@@ -6,11 +6,6 @@ go generate gonum.org/v1/gonum/unit
 go generate gonum.org/v1/gonum/unit/constant
 go generate gonum.org/v1/gonum/graph/formats/dot
 
-# Discard changes to go.mod that have been made.
-# FIXME(kortschak): Sort out a policy of what we should do with go.mod changes.
-# If we want to check changes we should set `GOFLAGS=-mod=readonly` in .travis.yml.
-git checkout -- go.{mod,sum}
-
 if [ -n "$(git diff)" ]; then	
 	git diff
 	exit 1

.travis/script.d/deps.sh

@@ -2,6 +2,14 @@
 
 set -ex
 
+# Avoid contaminating the go.mod/go.sum files.
+WORK=$(mktemp -d)
+pushd $WORK
+
+# Work around go1.11 issue where go get will not work outside a module.
+# TODO(kortschak): Remove when go1.11 is no longer supported.
+go mod init fake || true
+
 # Required for format check.
 go get golang.org/x/tools/cmd/goimports
 # Required for imports check.
@@ -13,3 +21,8 @@ go get golang.org/x/tools/cmd/cover
 go get github.com/mattn/goveralls
 # Required for dot parser checks.
 ${TRAVIS_BUILD_DIR}/.travis/script.d/install-gocc.sh 66c61e91b3657c517a6f89d2837d370e61fb9430
+
+# Clean up.
+# TODO(kortschak): Remove when go1.11 is no longer supported.
+popd
+rm -rf $WORK