Handle absent 'crypto' as per nodejs docs

[mihailik]

TypeScript Version: 2.4.0 / nightly (2.5.0-dev.201xxxxx)

TypeScript compiler relies on node's 'crypto' module unconditionally:

https://github.com/Microsoft/TypeScript/blob/6997e9b7316b081f8731d131139c7d7f1bba9092/src/compiler/sys.ts#L132

Whereas node's documentation for crypto module explicitly states:

Determining if crypto support is unavailable

It is possible for Node.js to be built without including support for the crypto module. In such cases, calling require('crypto') will result in an error being thrown.

let crypto;
try {
  crypto = require('crypto');
} catch (err) {
  console.log('crypto support is disabled!');
}

That means on a reduced node environment the compiler crashes unnecessarily. By unnecessarily I mean the support for crypto is already optional in the compiler:

https://github.com/Microsoft/TypeScript/blob/6997e9b7316b081f8731d131139c7d7f1bba9092/src/compiler/sys.ts#L67

https://github.com/Microsoft/TypeScript/blob/d7269f1386bb1ad4351a6f6d5f749e89cb14c2b7/src/compiler/watch.ts#L635

https://github.com/Microsoft/TypeScript/blob/67a6a9477f90d61955f92fb33e7b11491dbd17a5/src/compiler/program.ts#L165

Expected behavior:

TSC to work without 'crypto'

Actual behavior:

TSC fails without 'crypto'

[mihailik]

Note that one place in the code actually does rely on createHash unconditionally. Which should be a bug, considering that it's declared as optional in sys.ts line 67 (see above).

https://github.com/Microsoft/TypeScript/blob/a7fa187fb2ac58892593e8936ac728d61a57eacb/src/compiler/program.ts#L135

[mhegazy]

That means on a reduced node environment the compiler crashes unnecessarily.

Can you elaborate on what scenarios require node without crypto?

[mihailik]

@mhegazy three scenarios [UPDATED]:

• running non-standard node in a resource- or security-constrained environment (see node#5611 for their explicit support of this scenario)
• running in emulated environment (browserify, webpack etc.)
• building node from source and omitting openssl/crypto for random reason (see StackOverflow question or another nodejs post)

Here's a very relevant piece in node's lib/internal/util.js L100:

const noCrypto = !process.versions.openssl;
exports.assertCrypto = function(exports) {
  if (noCrypto)
    throw new Error('Node.js is not compiled with openssl crypto support');
};

[DanielRosenwasser]

We're going to need some sort of hashing mechanism at some point, we should just use that as a fallback for createHash. In the mean time, I'm not sure if there's any harm in being precautious.

[rbuckton]

@DanielRosenwasser: https://github.com/Microsoft/TypeScript/blob/vfs/src/harness/core.ts#L609