feat: dedupe - display difference when --dry-run is enabled (#7133)

* Added pretty print for dedupe command with --dry-run flag

* pretty print test coverage

lib/utils/reify-output.js

@@ -41,6 +41,10 @@ const reifyOutput = (npm, arb) => {
   }
 
   if (diff) {
+    if (npm.config.get('dry-run')) {
+      printDiff(npm, diff)
+    }
+
     depth({
       tree: diff,
       visit: d => {
@@ -98,6 +102,35 @@ const printAuditReport = (npm, report) => {
   npm.output(`\n${res.report}`)
 }
 
+// print the diff tree of actions that would be taken
+const printDiff = (npm, diff) => {
+  const msg = []
+
+  for (let i = 0; i < diff.children.length; ++i) {
+    const child = diff.children[i]
+    msg.push('\n', child.action.toLowerCase(), '\t')
+
+    switch (child.action) {
+      case 'ADD':
+        msg.push([child.ideal.name, child.ideal.package.version].join('\t'))
+        break
+      case 'REMOVE':
+        msg.push([child.actual.name, child.actual.package.version].join('\t'))
+        break
+      case 'CHANGE':
+        msg.push(
+          [
+            child.actual.name,
+            child.actual.package.version + ' -> ' + child.ideal.package.version,
+          ].join('\t')
+        )
+        break
+    }
+  }
+
+  npm.output(msg.join(''))
+}
+
 const getAuditReport = (npm, report) => {
   if (!report) {
     return

test/lib/utils/reify-output.js

@@ -380,3 +380,47 @@ t.test('added packages should be looked up within returned tree', async t => {
     t.matchSnapshot(out)
   })
 })
+
+t.test('prints dedupe difference', async t => {
+  const mock = {
+    actualTree: {
+      name: 'foo',
+      inventory: {
+        has: () => false,
+      },
+    },
+    diff: {
+      children: [
+        { action: 'ADD', ideal: { name: 'foo', package: { version: '1.0.0' } } },
+        { action: 'REMOVE', actual: { name: 'bar', package: { version: '1.0.0' } } },
+        {
+          action: 'CHANGE',
+          actual: { name: 'bar', package: { version: '1.0.0' } },
+          ideal: { package: { version: '2.1.0' } },
+        },
+      ],
+    },
+  }
+
+  const out = await mockReify(t, mock, {
+    'dry-run': true,
+  })
+
+  t.match(
+    out,
+    'add\tfoo\t1.0.0',
+    'should print added package'
+  )
+
+  t.match(
+    out,
+    'remove\tbar\t1.0.0',
+    'should print removed package'
+  )
+
+  t.match(
+    out,
+    'change\tbar\t1.0.0 -> 2.1.0',
+    'should print changed package'
+  )
+})