Have nonull: true cause the task to warn and abort.

Gruntfile.js

@@ -48,11 +48,6 @@ module.exports = function(grunt) {
           'tmp/custom_options': ['test/fixtures/file1', 'test/fixtures/file2']
         }
       },
-      handling_invalid_files: {
-        src: ['test/fixtures/file1', 'invalid_file/should_warn/but_not_fail', 'test/fixtures/file2'],
-        dest: 'tmp/handling_invalid_files',
-        nonull: true
-      },
       process_function: {
         options: {
           process: function(src, filepath) {
@@ -160,6 +155,31 @@ module.exports = function(grunt) {
 
   });
 
+  // Encapsulates tasks which invoke `grunt.fail.warn` and should abort.
+  grunt.registerTask('concat-warn', function() {
+    grunt.config('concat', {
+      handling_invalid_files: {
+        src: ['test/fixtures/file1', 'invalid_file/should_warn/and_abort', 'test/fixtures/file2'],
+        dest: 'tmp/handling_invalid_files',
+        nonull: true
+      }
+    });
+    grunt.task.run(['concat']);
+  });
+
+  // Encapsulates tasks which invoke `grunt.fail.warn` and should abort, but the
+  // test is checking behavior in the case of a user-specified `--force` flag.
+  grunt.registerTask('concat-force', function() {
+    grunt.config('concat', {
+      handling_invalid_files_force: {
+        src: ['test/fixtures/file1', 'invalid_file/should_warn/but_not_fail', 'test/fixtures/file2'],
+        dest: 'tmp/handling_invalid_files_force',
+        nonull: true
+      }
+    });
+    grunt.task.run(['concat']);
+  });
+
   // Actually load this plugin's task(s).
   grunt.loadTasks('tasks');
 

README.md

@@ -235,7 +235,7 @@ grunt.initConfig({
 ```
 
 #### Invalid or Missing Files Warning
-If you would like the `concat` task to warn if a given file is missing or invalid be sure to set `nonull` to `true`:
+If you would like the `concat` task to warn and abort if a given file is missing or invalid be sure to set `nonull` to `true`:
 
 ```js
 grunt.initConfig({
@@ -249,6 +249,8 @@ grunt.initConfig({
 });
 ```
 
+Additionally invoke grunt with `--force` to skip over missing files.
+
 See [configuring files for a task](http://gruntjs.com/configuring-tasks#files) for how to configure file globbing in Grunt.
 
 
@@ -298,4 +300,4 @@ grunt.initConfig({
 
 Task submitted by ["Cowboy" Ben Alman](http://benalman.com/)
 
-*This file was generated on Wed Apr 20 2016 08:41:44.*
+*This file was generated on Sun Jun 05 2016 08:36:20.*

docs/concat-examples.md

@@ -136,7 +136,7 @@ grunt.initConfig({
 ```
 
 ## Invalid or Missing Files Warning
-If you would like the `concat` task to warn if a given file is missing or invalid be sure to set `nonull` to `true`:
+If you would like the `concat` task to warn and abort if a given file is missing or invalid be sure to set `nonull` to `true`:
 
 ```js
 grunt.initConfig({
@@ -150,6 +150,8 @@ grunt.initConfig({
 });
 ```
 
+Additionally invoke grunt with `--force` to skip over missing files.
+
 See [configuring files for a task](http://gruntjs.com/configuring-tasks#files) for how to configure file globbing in Grunt.
 
 

tasks/concat.js

@@ -60,62 +60,80 @@ module.exports = function(grunt) {
       sourceMap = false;
     }
 
-    // Iterate over all src-dest file pairs.
-    this.files.forEach(function(f) {
-      // Initialize source map objects.
-      var sourceMapHelper;
-      if (sourceMap) {
-        sourceMapHelper = sourcemap.helper(f, options);
-        sourceMapHelper.add(banner);
-      }
-
-      // Concat banner + specified files + footer.
-      var src = banner + f.src.filter(function(filepath) {
-        // Warn on and remove invalid source files (if nonull was set).
-        if (!grunt.file.exists(filepath)) {
-          grunt.log.warn('Source file "' + filepath + '" not found.');
-          return false;
-        }
-        return true;
-      }).map(function(filepath, i) {
-        if (grunt.file.isDir(filepath)) {
-          return;
-        }
-        // Read file source.
-        var src = grunt.file.read(filepath);
-        // Process files as templates if requested.
-        if (typeof options.process === 'function') {
-          src = options.process(src, filepath);
-        } else if (options.process) {
-          src = grunt.template.process(src, options.process);
-        }
-        // Strip banners if requested.
-        if (options.stripBanners) {
-          src = comment.stripBanner(src, options.stripBanners);
+    var exitEarly = {};
+    try {
+      // Iterate over all src-dest file pairs.
+      this.files.forEach(function(f) {
+        // Initialize source map objects.
+        var sourceMapHelper;
+        if (sourceMap) {
+          sourceMapHelper = sourcemap.helper(f, options);
+          sourceMapHelper.add(banner);
         }
-        // Add the lines of this file to our map.
-        if (sourceMapHelper) {
-          src = sourceMapHelper.addlines(src, filepath);
-          if (i < f.src.length - 1) {
-            sourceMapHelper.add(options.separator);
+
+        // Concat banner + specified files + footer.
+        var src = banner + f.src.filter(function(filepath) {
+          // Warn on invalid source files (if nonull was set). They will be
+          // removed if --force is specified.
+          if (!grunt.file.exists(filepath)) {
+            grunt.fail.warn('Source file "' + filepath + '" not found.');
+            if (!grunt.option('force')) {
+              // See the catch clause below for why we do this.
+              throw exitEarly;
+            }
+            return false;
           }
-        }
-        return src;
-      }).join(options.separator) + footer;
+          return true;
+        }).map(function(filepath, i) {
+          if (grunt.file.isDir(filepath)) {
+            return;
+          }
+          // Read file source.
+          var src = grunt.file.read(filepath);
+          // Process files as templates if requested.
+          if (typeof options.process === 'function') {
+            src = options.process(src, filepath);
+          } else if (options.process) {
+            src = grunt.template.process(src, options.process);
+          }
+          // Strip banners if requested.
+          if (options.stripBanners) {
+            src = comment.stripBanner(src, options.stripBanners);
+          }
+          // Add the lines of this file to our map.
+          if (sourceMapHelper) {
+            src = sourceMapHelper.addlines(src, filepath);
+            if (i < f.src.length - 1) {
+              sourceMapHelper.add(options.separator);
+            }
+          }
+          return src;
+        }).join(options.separator) + footer;
 
-      if (sourceMapHelper) {
-        sourceMapHelper.add(footer);
-        sourceMapHelper.write();
-        // Add sourceMappingURL to the end.
-        src += sourceMapHelper.url();
-      }
+        if (sourceMapHelper) {
+          sourceMapHelper.add(footer);
+          sourceMapHelper.write();
+          // Add sourceMappingURL to the end.
+          src += sourceMapHelper.url();
+        }
 
-      // Write the destination file.
-      grunt.file.write(f.dest, src);
+        // Write the destination file.
+        grunt.file.write(f.dest, src);
 
-      // Print a success message.
-      grunt.verbose.write('File ' + chalk.cyan(f.dest) + ' created.');
-    });
+        // Print a success message.
+        grunt.verbose.write('File ' + chalk.cyan(f.dest) + ' created.');
+      });
+    } catch (reason) {
+      if (reason === exitEarly) {
+        // grunt.fail.warn uses the "exit" library, which doesn't stop the
+        // process synchronously on Node.js 0.10 on Windows, which could result
+        // in files still being concatenated even when some are missing. See:
+        // https://github.com/nodejs/node-v0.x-archive/issues/3584#issuecomment-8034529
+        // Therefore, we throw a unique reference to emulate exiting early.
+        return;
+      }
+      throw reason;
+    }
   });
 
 };

test/concat_test.js

@@ -2,6 +2,11 @@
 
 var grunt = require('grunt');
 var comment = require('../tasks/lib/comment').init(grunt);
+var exec = require('child_process').exec;
+var path = require('path');
+var fs = require('fs');
+
+var execOptions = {cwd: path.join(__dirname, '..')};
 
 function getNormalizedFile(filepath) {
   return grunt.util.normalizelf(grunt.file.read(filepath));
@@ -27,13 +32,30 @@ exports.concat = {
     test.done();
   },
   handling_invalid_files: function(test) {
-    test.expect(1);
+    test.expect(3);
 
-    var actual = getNormalizedFile('tmp/handling_invalid_files');
-    var expected = getNormalizedFile('test/expected/handling_invalid_files');
-    test.equal(actual, expected, 'will have warned, but should not fail.');
+    exec('grunt concat-warn', execOptions, function(error, stdout) {
+      test.ok(stdout.indexOf('Warning:') > -1, 'should print a warning.');
+      test.ok(stdout.indexOf('Aborted due to warnings.') > -1, 'should abort.');
 
-    test.done();
+      fs.exists('tmp/handling_invalid_files', function(exists) {
+        test.ok(!exists, 'should not have created a file.');
+        test.done();
+      });
+    });
+  },
+  handling_invalid_files_force: function(test) {
+    test.expect(2);
+
+    exec('grunt concat-force --force', execOptions, function(error, stdout) {
+      test.ok(stdout.indexOf('Warning:') > -1, 'should print a warning.');
+
+      var actual = getNormalizedFile('tmp/handling_invalid_files_force');
+      var expected = getNormalizedFile('test/expected/handling_invalid_files_force');
+      test.equal(actual, expected, 'should not fail.');
+
+      test.done();
+    });
   },
   strip_banner: function(test) {
     test.expect(10);