[client] Cache preventing current cell from evaluating

[myyong]

When Radka makes a change to previous cells, she cannot force-evaluate current cell because it refers to cache.

[tpetricek]

Ah! This is because of the way we calculate hashes for cells. We are a bit inconsistent, actually.

In javascript.ts we have:

let allHash = Md5.hashStr(antecedents.map(a => a.hash).join("-") + source)

This concatenates all hashes of all dependencies and also the source code and hashes that. This is perfect, because if source code or dependency changes, we get a new hash - so changing some code that this cell depends on would also invalidate the cache.

In external.ts we have the same in bind when constructing node:

let allHash = Md5.hashStr(antecedents.map(a => a.hash).join("-") + exBlock.source)

However, we use wrong hash in the evaluate operation. In line 199 we have:

let hash = Md5.hashStr(src)

// And we use this hash later in:
let body = {"code": strippedSrc,
      "hash": hash,
      "files" : importedFiles,
      "frames": importedFrames}

This only hashes the current source code, so if an antecedent changes, we will use wrong cached result.

We should not be computing hash in evaluate at all - we already computed (a correct) one when doing bind so we can just use that - this should be accessible in externalNode.hash.

TLDR - replacing hash on line 227 with externalNode.hash should fix the issue!

[tpetricek]

This should now be fixed - can we close this @myyong ?