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Re: Generating missing depfiles by an automake based makefile

From: Dmitry Goncharov
Subject: Re: Generating missing depfiles by an automake based makefile
Date: Thu, 9 Feb 2023 18:24:27 -0500

On Thursday, February 9, 2023, Tom Tromey <tom@tromey.com> wrote:

It's been a long time since I worked on automake, but the dependency
tracking in automake is designed not to need to rebuild or pre-build dep
files.  Doing that means invoking the compiler twice, which is slow.
Instead, automake computes dependencies as a side effect of compilation.

The hello.Po example presented above computes depfiles as a side effect of compilation. Moreover, when hello.Po is absent that makefile compiles hello.o as a side effect of hello.Po computation. In total there is only one compilation.

What is the scenario where you both end up with an empty depfile and a
compilation that isn't out of date for some other reason?  That seems
like it shouldn't be possible.

When a depfile is missing (for any reason) the current automake makefile creates a dummy depfile. From that point on the user has to notice that make is no longer tracking dependencies and their build is incorrect.

I am asking if automake can be enhanced to do something similar to hello.Po example above, in those cases when make supports that.

Regards, Dmitry

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