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.nh 1 "Literature Survey"
How can it be possible that we have been misusing \fImake\fP for 20 years?
How can it be possible that behavior previously ascribed to \fImake\fP's
limitations is in fact a result of misusing it?
.LP
The author only started thinking
about the ideas presented in this paper
when faced with a number of ugly build problems on
utterly different projects,
but with common symptoms.
By stepping back from the individual projects,
and closely examining the thing they had in common, \fImake\fP,
it became possible to see the larger pattern.
Most of us are too caught up in the minutiae of just getting the rotten
build to work that we don't have time to spare for the big picture.
Especially when the item in question \[lq]obviously\[rq] works,
and has done so continuously for the last 20 years.
.LP
It is interesting that the problems of recursive \fImake\fP are rarely
mentioned in the very books Unix programmers rely on for accurate,
practical advice.
.nh 2 "The Original Paper"
The original
.I make
paper
[feld78]
contains no reference to recursive
.I make,
let alone any discussion as to the relative merits of whole project
.I make
over recursive
.I make.
.LP
It is hardly surprising that the original paper did not discuss recursive
\fImake\fP, Unix projects at the time usually \fIdid\fP fit into a single
directory.
.LP
It may be this which set the \[lq]one \f(CWMakefile\fP in every directory\[rq]
concept so firmly in the collective Unix development mind\[hy]set.
.nh 2 "GNU Make"
The GNU Make manual
[stal93]
contains several pages of material concerning
recursive
.I make,
however its discussion of the merits or otherwise
of the technique are limited to the brief statement that
.QP
\[lq]This technique is useful when you want to separate
makefiles for various subsystems that compose a larger system.\[rq]
.LP
No mention is made of the problems you may encounter.
.nh 2 "Managing Projects with Make"
The Nutshell Make book
[talb91]
specifically promotes recursive
.I make
over whole project
.I make
because
.QP
\[lq]The cleanest way to build is to put a separate description file in
each directory, and tie them together through a master description file
that invokes \fImake\fP recursively.  While cumbersome, the technique is
easier to maintain than a single, enormous file that covers multiple
directories.\[rq] (p. 65)
.LP
This is despite the book's advice only two paragraphs earlier that
.QP
\[lq]\fImake\fP is happiest when you keep all your files in a single
directory.\[rq] (p. 64)
.LP
Yet the book fails to discuss the contradiction in these two statements,
and goes on to describe one of the traditional ways of treating the
symptoms of incomplete DAGs caused by recursive \fImake\fP.
.LP
The book may give us a clue as to why recursive \fImake\fP has been used
in this way for so many years.  Notice how the above quotes confuse the
concept of a directory with the concept of a \f(CWMakefile\fP.
.LP
This paper suggests a simple change to the mind\[hy]set:
directory trees, however deep, are places to store files;
\f(CWMakefile\fPs are places to describe the relationships
between those files, however many.
.nh 2 "BSD Make"
The tutorial for BSD Make
[debo88]
says nothing at all about recursive \fImake\fP,
but it is one of the few which actually described,
however briefly,
the relationship between a \f(CWMakefile\fP and a DAG (p. 30).
There is also a wonderful quote
.QP
\[lq]If \fImake\fP doesn't do what you expect it to,
it's a good chance the \f(CWmakefile\fP is wrong.\[rq] (p. 10)
.LP
Which is a pithy summary of the thesis of this paper.
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