fix(@angular/cli): add a flag to let assets outside of outDir

On top of angular#7778
Fixes angular#8122

Author: hansl

packages/@angular/cli/lib/config/schema.json

@@ -72,6 +72,11 @@
                       "type": "string",
                       "default": "",
                       "description": "The output path (relative to the outDir)."
+                    },
+                    "allowOutsideOutDir": {
+                      "type": "boolean",
+                      "description": "Allow assets to be copied outside the outDir.",
+                      "default": false
                     }
                   },
                   "additionalProperties": false

packages/@angular/cli/models/webpack-configs/common.ts

@@ -95,12 +95,20 @@ export function getCommonConfig(wco: WebpackConfigOptions) {
       asset.output = asset.output || '';
       asset.glob = asset.glob || '';
 
-      // Prevent asset configurations from writing outside of the output path
+      // Prevent asset configurations from writing outside of the output path, except if the user
+      // specify a configuration flag.
+      // Also prevent writing outside the project path. That is not overridable.
       const fullOutputPath = path.resolve(buildOptions.outputPath, asset.output);
-      if (!fullOutputPath.startsWith(path.resolve(buildOptions.outputPath))) {
-        const message = 'An asset cannot be written to a location outside of the output path.';
+      if (!fullOutputPath.startsWith(projectRoot)) {
+        const message = 'An asset cannot be written to a location outside the project.';
         throw new SilentError(message);
       }
+      if (!fullOutputPath.startsWith(path.resolve(buildOptions.outputPath))) {
+        if (!asset.allowOutsideOutDir) {
+          const message = 'An asset cannot be written to a location outside of the output path.';
+          throw new SilentError(message);
+        }
+      }
 
       // Ensure trailing slash.
       if (isDirectory(path.resolve(asset.input))) {

packages/@angular/cli/models/webpack-configs/utils.ts

@@ -92,4 +92,5 @@ export interface AssetPattern {
   glob: string;
   input?: string;
   output?: string;
+  allowOutsideOutDir?: boolean;
 }