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Comment by ajross | Hacker News Reader

Honestly, that's just intractable. That can't be solved for the same reason that changes to the makefile itself can't be tracked. Changes to the structure of the build system aren't "dependencies" as commonly understood.

Almost all other systems have this flaw in some way as well. You can fool everything, because a system capable of not being fooled would literally have to reparse and rebuild everything from scratch.

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I would like to boast that I have clearly solved an intractable problem, since (as I said) I have tools that happily track this very thing. But the truth is that the idea that it is intractable is rubbish, rather than that I can achieve impossible things before breakfast. (-:

You've switched tack between "not such a big deal" and "can't be solved" in the space of two messages. Both of your extremes are wrong. The truth is that this is simply difficult and needs either improvements to compilers or, as in my case, add-on tools that replicate the compiler's pre-processing and emit both the redo-ifchange and the redo-ifcreate information.

Almost all other systems have this flaw because they require dependencies before a build. If recording dependencies after the build, the entire problem becomes very simple. See here:

http://news.dieweltistgarnichtso.net/posts/redo-gcc-automati...

The example above was of a change to the build structure (include path, specifically) which changes the dependency tree in a way that doesn't involve changes to the files themselves and will be invisible to make or other tools that use file timestamps. I pointed out that this was just one of a whole class of intractable problems with dependency tracking that we all choose to ignore. It can't be fixed, even in principle. The only truly sure way to know you're building correctly is to build from scratch. Everything else is just a heuristic.

Why do you think the problem can not be fixed?

Also, have you looked at the redo tool redo-ifcreate? http://news.dieweltistgarnichtso.net/bin/redo-sh.html

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