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Re: Thoughts on limiting the parallel build load, suggestion for a new "

From: Eldar Abusalimov
Subject: Re: Thoughts on limiting the parallel build load, suggestion for a new "-j auto" option
Date: Wed, 14 Mar 2012 18:29:40 +0400


I would suggest to mention the current behavior in the manual, instead of making $(value ...) to emit a warning. The main motivation is backward compatibility.

In our project we widely use $(value N) to get arguments of 'call' that are assumed to be optional without raising a warning (I've just found about 100 lines where we use it to suppress the warning). And we also always use make with '--warn-undefined-variables' flag too.

For example,

# Args:
#  1. A list to convert into a PATH variable.
#  2. (Optional) path separator to use. When empty, defaults to a colon.
    $(subst $(space),$(or $(value 2),$(colon)),$(strip $1))

This allows one to use $(call PATHIFY,foo bar) as well as $(call PATHIFY,bar baz,;).

Without using the 'value' function I would have to write something like:
    $(subst $(space),$(if $(and $(filter-out undefined,$(flavor 2)),$2),$2,$(colon)),$(strip $1))

The latter looks ugly and it is also much slower if the function is assumed to be called often. And all these drawbacks would be needed only to suppress a warning.

Well, in other word, I think about 'value' function as a kind of an introspection facility. It is much like as 'flavor' or 'origin' functions, which do not generate a warning for undefined variables. So I wish to leave the current behavior as is and to describe it in the manual.

2012/3/14 R. Diez <address@hidden>
Hi all:

Writing makefiles is hard enough, so I always enable option --warn-undefined-variables whenever I can.

I have recently realised that in GNU Make 3.81 the $(value ...) function does not warn as expected. That is, if I run this example makefile:


    echo "$($(VAR_NAME))"
    echo "$(value $(VAR_NAME))"

I get the following output:

Makefile:24: Warnung: undefinierte Variable »UNDEFINED_VARIABLE«
Makefile:24: Warnung: undefinierte Variable »UNDEFINED_VARIABLE«
echo ""
echo ""
echo ""

Is this an oversight? The manual does not mention any exceptions for --warn-undefined-variables, and I wish that $(value ...) warned too.

Please copy me on the answers, as I'm not subscribed to this list.

  R. Diez

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Best regards,
Eldar Sh. Abusalimov

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