Handling ShouldComponentUpdate throwing an exception

[danielcompton]

In

reagent/src/reagent/impl/component.cljs

Lines 160 to 172 in 1e19d31

	:shouldComponentUpdate
	(fn shouldComponentUpdate [nextprops nextstate]
	(or util/*always-update*
	(this-as c
	;; Don't care about nextstate here, we use forceUpdate
	;; when only when state has changed anyway.
	(let [old-argv ($ c :props.argv)
	new-argv ($ nextprops :argv)
	noargv (or (nil? old-argv) (nil? new-argv))]
	(cond
	(nil? f) (or noargv (not= old-argv new-argv))
	noargv (.call f c c (get-argv c) (props-argv c nextprops))
	:else (.call f c c old-argv new-argv))))))

the not= call on line 170 can throw. A minimal example of this is:

(= {:todos 1} (sorted-map 1 2))

This is being tracked in CLJ-2325. It only shows up when using custom types. I don't think it can occur in equality checks between the standard Clojure data structures. A similar issue will need to be raised in CLJS, once the approach to fix it is decided in CLJS.

In the meantime, I wonder if we should wrap not= calls here with a try/catch, returning false if it throws. I'm not sure what the performance impact of this is though?

An alternative approach is for developers to manually reset the key of the React component to force a component re-render.

[Deraen]

Related: #344

[Deraen]

#373 merged