Adds --debug and --dry-run options to metalsmith (build) command

bin/metalsmith

@@ -33,9 +33,13 @@ program
   .command('build', { isDefault: true })
   .description('Run a metalsmith build')
   .option('-c, --config <path>', 'configuration file location', 'metalsmith.json')
+  .option('--debug', 'Set or override debug namespaces')
+  .option('--dry-run', 'Process metalsmith files without outputting to the file system')
   .action(buildCommand)
 
-function buildCommand({ config }) {
+program.parse(process.argv)
+
+function buildCommand({ config, ...options }) {
   const dir = process.cwd()
   const path = isAbsolute(config) ? config : resolve(dir, config)
 
@@ -67,6 +71,7 @@ function buildCommand({ config }) {
   if (json.frontmatter != null) metalsmith.frontmatter(json.frontmatter)
   if (json.ignore != null) metalsmith.ignore(json.ignore)
   if (isObject(json.env)) metalsmith.env(expandEnvVars(json.env, process.env))
+  if (options.debug) metalsmith.env('DEBUG', options.debug)
 
   // set a flag plugins can check to target CLI-specific behavior
   metalsmith.env('CLI', true)
@@ -103,15 +108,18 @@ function buildCommand({ config }) {
     }
   })
 
-  /**
-   * Build.
-   */
-
-  metalsmith.build(function (err) {
-    if (err) fatal(err.message, err.stack)
-    log('success', `successfully built to ${metalsmith.destination()}`)
-  })
+  function onBuild(message) {
+    return (err) => {
+      if (err) fatal(err.message, err.stack)
+      log('success', message)
+    }
+  }
 
+  if (options.dryRun) {
+    metalsmith.process(onBuild(`successfully ran a dry-run of the ${config} build`))
+  } else {
+    metalsmith.build(onBuild(`successfully built to ${metalsmith.destination()}`))
+  }
 }
 
 /**

test/fixtures/cli-debug/expected/index.html

@@ -0,0 +1 @@
+body

test/fixtures/cli-debug/metalsmith.json

@@ -0,0 +1,8 @@
+{
+  "env": {
+    "debug": false
+  },
+  "plugins": {
+    "@metalsmith/markdown": {}
+  }
+}

test/fixtures/cli-debug/src/index.md

@@ -0,0 +1 @@
+body

test/fixtures/cli-dry-run/metalsmith.json

@@ -0,0 +1 @@
+{}

test/fixtures/cli-dry-run/src/index.md

@@ -0,0 +1 @@
+body

test/index.js

@@ -1325,5 +1325,23 @@ describe('CLI', function () {
         done()
       })
     })
+
+    it('should not output a build when the --dry-run option is used', function (done) {
+      exec(`${bin} --dry-run`, { cwd: fixture('cli-dry-run') }, function (err) {
+        assert.strictEqual(err, null)
+        fs.stat(fixture('cli-dry-run/build'), (err) => {
+          assert.strictEqual(err.code, 'ENOENT')
+          done()
+        })
+      })
+    })
+
+    it('should override metalsmith.json DEBUG env var when --debug option is used', function (done) {
+      exec(`${bin} --debug @metalsmith/markdown`, { cwd: fixture('cli-debug') }, function (err, stdout, stderr) {
+        const match = stderr.split('\n')[1].slice(stderr.indexOf(' ') + 1)
+        assert.strictEqual(match, '@metalsmith/markdown converting file: index.md')
+        done()
+      })
+    })
   })
 })