make(1), multiple directories and other enhancements

[utzoo!decvax!ucbvax!unix-wizards]

>From walton at LL-XN Thu Sep 10 19:27:17 1981
Andrew Knutsen at SRI-UNIX raised the question of make(1) and
multiple directories.  I do not know whether the following enhancements
to V7 make would help him, but they might, and might be of interest
to others.  What follows is a several page memo.  The .FILES feature
allows prerequisites to be in any directory; rather the inverse of
what Mr. Knutsen may have wanted, maybe. ---

LL-XN has a version of V7 make that has been reworked to allow
more complex systems to be easily handled.  The major goal was
to allow one piece of C code to be compiled on one computer
for several target operating systems and target computers.

The following are extra sections added to the manual to explain
the extra features and provide some necessary knowledge about the
standard features.  Also, effort was put into making the
program diagnose memory overflows better, and make more efficient
use of data memory.

 .SH ADDITIONS
The following are additions to the BELL V7 make.
 .PP
Macro names are expanded like other text, and so themselves may
contain macro names.  E.g. $($(SYS)LIBES) is allowed.  This provides
a kind of case statement for macro definitions which is sometimes
useful.
Macro names are also expanded when they appear on the left side of
a macro definition; but the expansion of the right side is delayed
until the macro is used.
 .PP
An entry with a name of the form .FILES.y for suffix .y may be used
to list all the allowable implicit prerequisite files with suffix .y.  The
dependants of .FILES.y are the allowed prerequisites.
If a file name f.x ends in a suffix .x, and if an implicit rule .y.x exists
for suffix .y, and if the entry .FILES.y exists, then .FILES.y
is made, and its dependency list is searched for an implicit
prerequisite name of the form f.y or <some_directory>/f.y.
If such a name is found, it is used as a prerequisite
with the shell commands of
the .y.x rule.  In any case if .FILES.y
exists the search of the current directory for the prerequisite f.y
is surpressed.
 .PP
Sometimes searches for implicit prerequisites fill up
memory with useless possible prerequisite names.  These can be
eliminated only by providing a .FILES.y entry for every possible
prerequisite suffix.
 .PP
The .INCLUDE statement may be use like the #include statement of the
C macro processor.  The syntax is
 .sp
	.INCLUDE "file"

	.INCLUDE <file>
 .sp
with the meaning that the file is inserted at the point the statement
appears.  If "" surrounds the file name, the file is first searched for
in the directory that contains the file which contains the .INCLUDE
statement.  If not found, the file is searched for in the directory
/usr/include.  If <> surrounds the file name, only /usr/include is
searched.  If the file name begins with a /, no directories are
searched and it is assumed that the full pathname has been given.
\&.INCLUDE statements may be nested.
The .INCLUDE must be at the very beginning of the line,
and any comments must follow the file name.
 .PP
Macros defined before a file is included may not be redefined during
the inclusion: the included definitions are overridden and ignored just as
such definitions are overridden and ignored by definitions appearing as
arguments.
Otherwise macro redefinitions are allowed provided the macro has not
yet been used.
An explicit exception to this rule is that builtin macros may always be
redefined anytime before they are used.
 .PP
The entry which is made by default if no argument lists an entry to
be made is the first file name encounterred which does not begin
with "." or which contains a "/": this is not an addition; it is
true of standard V7 make.  This means that the default entry
may come from a .INCLUDE file.
 .PP
The special suffix .NONE is known to make and should not appear in
the suffix list.  If a target file has no suffix from the .SUFFIX list,
it is considered to have the suffix .NONE for the purposes of implicit
prerequisite file searching.
Rules with names of the form <suffix>.NONE use this feature.
 .PP
If a rule exists with a name of the
form .NONE<suffix> then implied prerequisite files whose names
should be of the form <prefix>.NONE will in fact be taken to have
names of the form <prefix> with no extension.
 .PP
If a file name containing the meta-characters [, *, or ? does
not match any existing file, then the name is deleted as if it
did not exist, instead of being left unexpanded as in the shell
or standard V7 make.  This makes it easier for included makefiles
to serve many different systems, some of which may not have some
kinds of files.
 .SH REMARKS
The following are remarks on the detailed behavior of the standard
V7 make.
 .PP
For every target a search is made for an implied prerequisite file,
even if explicit rules for the target exist.  Any shell commands
provided by explicit rules override those provided by the implicit
rules,
but the target still depends upon the implicit prerequisite file.
If the target name is t.s1 and a rule named .s2.s1 exists and
the file t.s2 exists then t.s2 is necessarily a prerequisite for t.s1.
However, if there are several such prerequisite files, the search
stops after finding the first one.  The search checks the target
name for suffixes s1 first, and for each s1 that is a target suffix,
searches for possible s2 suffixes.  The order of the suffix searches
is that of the .SUFFIX list with .NONE added to the end.
 .PP
Normally shell commands are executed by calling the shell with the -e
option, which terminates the shell program whenever an error is
encountered, and in particular makes it impossible to put if, while,
and similar commands in the shell command line.
Putting a - at the begining of the shell command line surpresses the -e option.
The -e option does not affect shell programs invoked indirectly by
command names in the shell command; it only effects the shell commands
directly contained in the makefile.
 .PP
Whenever a ".SUFFIXES:" line with no dependents is read, all the
previous dependents of .SUFFIXES are discarded.
This provides a mechanism for clearing the suffix list prior to
rebuilding it with more .SUFFIXES lines.
 .PP
Whenever a line ".<something>:" is read, all previous shell command
lines for ".<something>" are discarded.  This is the mechanism that
allows redefinition of ".suffix1.suffix2".
 .PP
Macro calls are expanded immediately when encounterred in
prerequisite or dependant file names, on the leftside of
an equals sign in a macro definition,
or in .INCLUDE statements.
All other macro calls have
their expansion delayed.  Macro definitions are expanded when used,
and may expand differently than they would have expanded when the
macro was defined.  Similarly shell command lines are expanded when
used.
A macro may not be redefined after it is used.