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Idea: Add command-line option for reporting potential makefile errors

From: David A. Wheeler
Subject: Idea: Add command-line option for reporting potential makefile errors
Date: Tue, 11 Jun 2019 22:09:03 -0400 (EDT)


Makefiles often have errors, and they lay dormant because they're undetected.

On Tue, 11 Jun 2019 07:44:31 -0700, <address@hidden> wrote:
>  Considering that many build systems created with Make do not properly
>  perform incremental builds (because all the necessary rules are not
>  written, or are written incorrectly), it's also a way to trivially
>  make a build that is mysteriously broken because one or more files
>  will not be properly rebuilt.

Of course, that's a potential problem for *any* use of make.
Garbage in, garbage out.  I use automated dependency generation
where I can, but the generators can have bugs & not
all situations have a generator.

Potential solution:

Perhaps there should be a make flag that attempts to detect & warn
about missing dependency information during make execution,
to help people fix their makefiles.

Basically, when running a rule, make could enable strace to see
what is *actually* getting checked/read & written, compare that to what the
rule *claims* are the prerequisites & targets, and then complain about 

I did some brief experiments using:
 strace -f -e trace=%file gcc -o b.o b.c

As expected, there are a huge number of special-case events.
But if you only consider file-related events in a specific directory or down
(which could probably default to the current directory), including
relative paths, most of the events that would not normally go in a
makefile disappear. It's also helped if you limit the set of system calls that
need to be considered (e.g., openat is really important on Ubuntu).

It might be much easier if this required other tools (like strace) to work,
instead of directly implementing the tracing in make.
This mechanism could be slow, but that's okay; I envision doing this
checking occasionally, instead of doing it on every run.
This might not be implemented on all platforms, but it would be useful
on many platforms & help people fix their makefiles for all.

--- David A. Wheeler

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