refactor: add normalizePackageMan helper (#100)

## What / Why
Aligns normalization logic with `directories.bin`

See also:
https://github.com/npm/normalize-package-data/blob/main/lib/fixer.js#L105
```js
  fixManField: function (data) {
    if (!data.man) {
      return
    }
    if (typeof data.man === 'string') {
      data.man = [data.man]
    }
  },
```

## References
* continues npm/read-package-json#177
* relates #104

CC @wraithgar

Author: antongolub

lib/normalize.js

@@ -83,11 +83,36 @@ function normalizePackageBin (pkg, changes) {
   delete pkg.bin
 }
 
+function normalizePackageMan (pkg, changes) {
+  if (pkg.man) {
+    const mans = []
+    for (const man of (Array.isArray(pkg.man) ? pkg.man : [pkg.man])) {
+      if (typeof man !== 'string') {
+        changes?.push(`removed invalid "man [${man}]"`)
+      } else {
+        mans.push(unixifyPath(securePath(unixifyPath(man))))
+      }
+    }
+
+    if (!mans.length) {
+      changes?.push('empty "man" was removed')
+    } else {
+      pkg.man = mans
+      return pkg
+    }
+  }
+  delete pkg.man
+}
+
 function isCorrectlyEncodedName (spec) {
   return !spec.match(/[/@\s+%:]/) &&
     spec === encodeURIComponent(spec)
 }
 
+function unixifyPath (ref) {
+  return ref.replace(/\\|:/g, '/')
+}
+
 function isValidScopedPackageName (spec) {
   if (spec.charAt(0) !== '@') {
     return false
@@ -329,13 +354,16 @@ const normalize = async (pkg, { strict, steps, root, changes, allowLegacyCase })
   }
 
   // expand directories.man
-  if (steps.includes('mans') && !data.man && data.directories?.man) {
-    const manDir = data.directories.man
-    const cwd = path.resolve(pkg.path, securePath(manDir))
-    const files = await lazyLoadGlob()('**/*.[0-9]', { cwd })
-    data.man = files.map(man =>
-      path.relative(pkg.path, path.join(cwd, man)).split(path.sep).join('/')
-    )
+  if (steps.includes('mans')) {
+    if (data.directories?.man && !data.man) {
+      const manDir = unixifyPath(securePath(unixifyPath(data.directories.man)))
+      const cwd = path.resolve(pkg.path, manDir)
+      const files = await lazyLoadGlob()('**/*.[0-9]', { cwd })
+      data.man = files.map(man =>
+        path.relative(pkg.path, path.join(cwd, man)).split(path.sep).join('/')
+      )
+    }
+    normalizePackageMan(data, changes)
   }
 
   if (steps.includes('bin') || steps.includes('binDir') || steps.includes('binRefs')) {

test/prepare.js

@@ -154,6 +154,105 @@ for (const [name, testPrepare] of Object.entries(testMethods)) {
       t.end()
     })
 
+    t.test('man', t => {
+      t.test('resolves directory', async t => {
+        const { content } = await testPrepare(t, ({
+          'package.json': JSON.stringify({
+            directories: { man: './man' },
+          }),
+          man: { man1: { 'test.1': 'man test file' } },
+        }))
+        t.strictSame(content.man, ['man/man1/test.1'])
+      })
+
+      if (name === '@npmcli/package-json') {
+        t.test('non-string', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              man: 123,
+            }),
+          }))
+          t.has(content, { man: undefined })
+        })
+
+        t.test('good', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              man: './man/test.1',
+            }),
+          }))
+          t.strictSame(content.man, ['man/test.1'])
+        })
+
+        t.test('empty', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              man: [],
+            }),
+          }))
+          t.has(content, { man: undefined })
+        })
+
+        t.test('directories.man no prefix', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              name: 'man-test',
+              directories: {
+                man: './man',
+              },
+            }),
+            man: { 'test.1': '.TH man "test man page"' },
+          }))
+          t.strictSame(content.man, ['man/test.1'])
+        })
+
+        t.test('directories.man trim prefix', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              name: 'man-test',
+              directories: {
+                man: '../../../../../man',
+              },
+            }),
+            man: { 'test.1': '.TH man "test man page"' },
+          }))
+          t.strictSame(content.man, ['man/test.1'])
+        })
+
+        t.test('directories.man handles reversed slashes', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              name: 'man-test',
+              directories: {
+                man: '..\\..\\man',
+              },
+            }),
+            man: { 'test.1': '.TH man "test man page"' },
+          }))
+          t.strictSame(content.man, ['man/test.1'])
+        })
+
+        t.test('directories.man with man', async t => {
+          const { content } = await testPrepare(t, ({
+            'package.json': JSON.stringify({
+              name: 'man-test',
+              directories: {
+                man: './man',
+              },
+              man: '../../test.2',
+            }),
+            man: {
+              'test.1': '.TH man "test man page 1"',
+              'test.2': '.TH man "test man page 2"',
+            },
+          }))
+          t.strictSame(content.man, ['test.2'])
+        })
+      }
+
+      t.end()
+    })
+
     t.test('bundleDependencies', t => {
       t.test('true', async t => {
         const { content } = await testPrepare(t, ({
@@ -325,19 +424,6 @@ for (const [name, testPrepare] of Object.entries(testMethods)) {
       t.end()
     })
 
-    t.test('man', t => {
-      t.test('resolves directory', async t => {
-        const { content } = await testPrepare(t, ({
-          'package.json': JSON.stringify({
-            directories: { man: './man' },
-          }),
-          man: { man1: { 'test.1': 'man test file' } },
-        }))
-        t.strictSame(content.man, ['man/man1/test.1'])
-      })
-      t.end()
-    })
-
     t.test('gitHead', t => {
       t.test('HEAD with no ref', async t => {
         const { content } = await testPrepare(t, ({