Analyzer Improvements

[zampino]

• Simplify Graph nodes (each code block appears in the graph just once by its block-id)
• Simplify hash of deps (only graph dependencies are used to compute the hash of a block)
• Improve assertion on missing hash for dependencies
• Take var snapshots during eval
• Don't make expressions depend on forward declarations, but only on actual definitions
• Handle var redefinitions (all blocks with redefined vars are not cached)

Fixes #454 Fixes #628 Fixes #66 Fixes #634

[zampino]

Some edge cases still need to be addressed:

(def a 1)

(def a (inc a))

a

the analyzer/analyze fails to return a as dependency of the (def a (inc a)). This is because we set-subtract all introduced vars from the deps: https://github.com/nextjournal/clerk/blob/38a4653492bd47799f6dc5e6864e2b7eaf47a410/src/nextjournal/clerk/analyzer.clj#L187 Not doing that leads to other issues (e.g for multi-arity defns (defn f ([x] (f {} x)) ([x opts] ...)).

So when the first definition changes, this won't propagate to the value of a at the bottom. It's still an improvement wrt main, where the code above just crashes (#634).

[zampino]

Second case:

(def a 1)

(inc a)

(def a :boom)

Similarly, this also crashes on main (#634) but evals correctly a first time on this branch.

Subsequent clerk/show! fail when the consumer of the var a changes, since a is bound to a keyword, but (def a 1) didn't change. A similar behaviour to the "deref deps" might be applied here, but we need to decide when.

[zampino]

Of course I didn't thought of the example:

(def a 1)
(when false (def a 2))
(inc a)

so also the current handling of redefinitions in the graph won't work reliably, I'm tempted to not cache definitions with the same name at all and let people decide (throw on redefs, warn+not-cache, not-cache).

[zampino]

In this other branch I've disabled caching for redefined vars (and therefore for their dependants). We might mark in the UI the blocks that are not cached and in case of the redefinitions explain why.

[zampino]

Trying out passing info to code cells

https://github.com/nextjournal/clerk/assets/1078464/7f11c5db-3243-4681-bed5-1729a94e759a