Variable file() path isn't parsed if it contains `@`

This is a Bug Report

Description

I’m trying to load variables from a scoped npm module in serverless.yml:

custom:
  variableFromFile: ${file(node_modules/@scope/module-name/variables.json):variableName}

But when I try to deploy the service, I get the following error:

TypeError: Cannot read property 'Policies' of undefined
    at functionObj.events.forEach.event (/Users/adam/.config/yarn/global/node_modules/serverless/lib/plugins/aws/package/compile/events/stream/index.js:182:18)
    at Array.forEach (<anonymous>)
    at serverless.service.getAllFunctions.forEach (/Users/adam/.config/yarn/global/node_modules/serverless/lib/plugins/aws/package/compile/events/stream/index.js:41:28)
    at Array.forEach (<anonymous>)
    at AwsCompileStreamEvents.compileStreamEvents (/Users/adam/.config/yarn/global/node_modules/serverless/lib/plugins/aws/package/compile/events/stream/index.js:16:47)
    at BbPromise.reduce (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:366:55)
From previous event:
    at PluginManager.invoke (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:366:22)
    at PluginManager.spawn (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:384:17)
    at Deploy.BbPromise.bind.then.then (/Users/adam/.config/yarn/global/node_modules/serverless/lib/plugins/deploy/deploy.js:120:50)
From previous event:
    at Object.before:deploy:deploy [as hook] (/Users/adam/.config/yarn/global/node_modules/serverless/lib/plugins/deploy/deploy.js:110:10)
    at BbPromise.reduce (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:366:55)
From previous event:
    at PluginManager.invoke (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:366:22)
    at PluginManager.run (/Users/adam/.config/yarn/global/node_modules/serverless/lib/classes/PluginManager.js:397:17)
    at variables.populateService.then (/Users/adam/.config/yarn/global/node_modules/serverless/lib/Serverless.js:104:33)
    at runCallback (timers.js:785:20)
    at tryOnImmediate (timers.js:747:5)
    at processImmediate [as _immediateCallback] (timers.js:718:5)
From previous event:
    at Serverless.run (/Users/adam/.config/yarn/global/node_modules/serverless/lib/Serverless.js:91:74)
    at serverless.init.then (/Users/adam/.config/yarn/global/node_modules/serverless/bin/serverless:42:50)
    at <anonymous>

If I copy the JSON file to a path that doesn’t contain the @ symbol, it works.

Additional Data

• Serverless Framework Version you’re using: 1.24.1
• Operating System: OSX

[HyperBrain]

We should rather go for a blacklist regex here: /^file\(([^?%*:|"<>]+?)\)/

I’m not sure why the file syntax does not even allow for absolute paths. Imo we should allow these. The regex I wrote above seems to be suitable. It allows for any valid filename.

[HyperBrain]

The reason for this bug is quite simple. The regex we use to parse the file variable syntax just does not allow for @.

/^file\((~?[a-zA-Z0-9._\-/]+?)\)/

So only alphanumeric characters are allowed including slashes, underscores and dashes. BTW: Using Windows path separators will also break 🤔

We should instead use a regex that really matches file paths (including \ and some special characters.