[nickpsecurity]

"rewritten the majority of its source code with web standards and interoperability with other modern browsers in mind"

I think coldtea is focusing on highlighted part. A rewrite like that might change so many behavioral aspects, esp user- or developer-visible, that it can be considered a new engine rather than mere clean-up of behaviorally-identical old one. I certainly reuses some code and techniques but differences might be major.

[kbenson]

At the same time, depending on how the rewrite was carried out, it may be nothing like a completely new project. Rewriting function by function is different than rewriting component by component, which is also different than rewriting from scratch.

Rewriting function by function will give you largely the same program using largely the same algorithms, but possibly with more or less bugs, or cleaned up code.

Rewriting component by component will allow new ways those components are implemented, but the interface between components will likely be the same.

Rewriting from scratch could yield anything (servo could be classified as a way to rewrite gecko from scratch, I believe).

All of these could be said to have had the majority of their source code rewritten, but I would only really consider the last one to be "new" without knowing further details. Of course, the devil is in the details...

[nickpsecurity]

It's why I'm focusing on behavioral aspect: what does the software do? A browser fork that behaves very differently from prior one to point you have to change existing code to get same effect is essentially a new app at behavioral level. However, it might have same name and lots of same code inside. At that level, it's old code in an old app. We largely define our components by their interfaces and behavior. So that's what I'm focusing on.

[kbenson]

Sure, but if it behaves significantly differently, then I think that precludes it from being a function by function rewrite. At the same time, a component by component rewrite can be a complete rewrite (but it depends a bit more on the details, I think). If the mainly user visible portions are rewritten, but much of the utility code and other components are not, it may appear behaviorally different, but but be largely the same code base. It's much harder to know, looking in from the outside.

For a simplistic example, say someone provides a "rewrite" of grep. Maybe the options are all different looking and sounding, so it may appear to be significantly different. But if the core of the matching algorithm and it's capabilities are largely unchanged, is it a that much of a rewrite? To the outside user it may superficially appear so, but to someone comparing the source from before and after, there may be an entirely different opinion, and even that may change if you come from a context of focusing on a particular aspect.

As applied to Trident/Edge, we may have a case where the person speaking was involved in a project to rewrite one major component of the browser, and so is speaking in that context. Maybe that component is responsible for about 60% of the code and functionality, but it still relies on a quite a bit of largely unchanged additional libraries. It's very subjective as to whether you think that qualifies as a rewrite of the project, and depends quite a bit on what was not rewritten, and what you think of that code.

[nickpsecurity]

Re rewrite differences

Let's look at the grep example agsin. If it did same thing, but new interface, then it would be same thing because behavior is otherwise the same. Now, lets say you changed what pattern-matching itself produced where you no longer got the same results from same text. Matched totally different patterns unless you changed the text you are inputting to get same results again. And the interface was different. Is that still grep?

If he's talking one component, maybe not anything new underneath. He said the engine (rendering) would be more standards compliant and compatible with other browsers. That's basically what Opera and Mozilla did many years ago while IE didnt. If you blocked out the name, nobody using the browser would think they were using same app when they saw rendering hit those aspects totally distorting the presentation. Or had to redo their websites to display correctly. I remember reading many complaints from web developers about making stuff work with several, different engines whose rendering argued.

So, if Edge engine is different enough to cause that, then it seems like a different engine at behavioral level given same input leads to different output that fails acceptance. Nobody would think it was same app unless the UI told them.

I mean, I still think sameness or newness is an open issue. Do we judge it be function and component as you added? Or interface and behavioral spec as I was looking at? One might also look at data formats. I think it will best to technically just compare in various ways to be accurate. Feature-driven development field probably has some insight into this. However, users will look at them as different, at least in a version since, if they can't do what they were used for or break compatibility. The two Python versions are possibly a good example.

[kbenson]

> Let's look at the grep example agsin. If it did same thing, but new interface, then it would be same thing because behavior is otherwise the same.

That sort of depends on how you define "behavior". More specifically, if it matches something equivalent but different to regular expressions (even if it's just a character transliteration to regular expression syntax), then does the behavior change? Is that still grep? Maybe, if grep decides the the "new grep2 have an easier to learn matching language". It's not like we haven't seen that before.

> I mean, I still think sameness or newness is an open issue.

Sure! The vast majority of cases it probably is an open issue, because different people have different criteria. I was just pointing out that the wording from MS doesn't necessarily imply a rewrite as many people might define it, because we have very little context to go on in the statement, and different people have different ideas about what is the browser. The rendering engine? The UI? The JS VM? All of them combined?

I can totally see someone responsible for the rendering engine saying "we rewrote most of the source code" and the JS VM guys scratching their heads wondering what the hell they are talking about, because they definitely didn't rewrite most their code, and they think their component is a significant portion of the browser...