Add CI check to ensure module definition is correct (#198)

* Add CI check to ensure module definition is correct

Fail verification if "go mod tidy" results in any modifications
to go.mod or go.sum.

* Improve pipeline

* Use script

* Add working directory

* Fix module definition script for Windows

* Add git configuration for autocrlf

* Simplify

* Revert "Simplify"

This reverts commit b7d8b0f.

* Flip core.autocrlf

* Add .gitattributes to prevent line ending conversion

* Try approach without .gitattributes

* Add checkout step

azure-pipelines.yml

@@ -26,6 +26,12 @@ variables:
   #GO111MODULE: on
 
 steps:
+
+- bash: git config --global core.autocrlf false
+  displayName: "Disable line ending conversion for git to"
+
+- checkout: self
+
 - bash: |
     latestGo=$(curl "https://golang.org/VERSION?m=text")
     echo "##vso[task.setvariable variable=LATEST_GO]$latestGo"
@@ -78,6 +84,21 @@ steps:
     env
   displayName: Print Go version and environment
 
+- bash: |
+    go mod tidy
+    if [ ! -z "$(git status --porcelain go.mod)" ]; then
+      printf "go.mod has modifications\n"
+      git diff go.mod
+      exit 1
+    fi
+    if [ ! -z "$(git status --porcelain go.sum)" ]; then
+      printf "go.sum has modifications\n"
+      git diff go.sum
+      exit 1
+    fi
+  workingDirectory: '$(modulePath)'
+  displayName: Ensure that module definition and checksums are correct
+
 - script: |
     go get -v -t -d ./...
     golangci-lint run -E gofmt -E goimports -E misspell