Extract gomodifytags into a library

.github/workflows/go.yml

@@ -1,25 +1,50 @@
 name: build
-on: [push, pull_request]
-jobs:
 
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
   test-build:
     name: Test & Build
     runs-on: ubuntu-latest
     steps:
 
-    - name: Set up Go 1.15
-      uses: actions/setup-go@v1
+    - name: Set up Go
+      uses: actions/setup-go@v2
       with:
-        go-version: 1.15
-      id: go
+        go-version: ^1.17
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
+
+    - name: Run go mod tidy
+      run: |
+        set -e
+        go mod tidy
+        output=$(git status -s)
+        if [ -z "${output}" ]; then
+         exit 0
+        fi
+        echo 'We wish to maintain a tidy state for go mod. Please run `go mod tidy` on your branch, commit and push again.'
+        echo 'Running `go mod tidy` on this CI test yields with the following changes:'
+        echo "$output"
+        exit 1
 
     - name: Test
       run: |
-        go mod tidy -v
         go test -race ./...
 
+    - name: Go vet
+      run: "go vet ./..."
+
+    - name: Staticcheck
+      uses: dominikh/[email protected]
+      with:
+        version: "2021.1.1"
+        install-go: false
+
     - name: Build
       run: go build ./...