Make ends up deleting source files

[Krishnakumar B]

Hi,

I am seeing a problem with the semantics of pattern matching with GNU Make.
My example Makefile is as follows:

#----------------------------------------------------------------------------
#       $Id: Makefile,v 1.17 2002/02/15 12:50:37 kitty Exp $
#
#----------------------------------------------------------------------------

# List of all files that make up the project
#
FILES   = director              \
          player                \
          player_driver         \
          director_driver       \
          script

# List of all the source files that we will use
#
SRC     = $(addsuffix .cc, $(FILES))

OBJS    = $(SRC:%.cc=%.o)

realclean:
        -$(RM) $(BIN) $(OBJS)


The problem is with OBJS. I am trying to extract the names of the object
files from the source files. This works fine when my files in the directory
end with .cc. But if by mistake, if OBJS is defined as follows:

OBJS  = $(SRC:%.cpp=%.o) or OBJS = $(SRC:.cpp=.o)

then the pattern matches end up not finding the .cpp in SRC and hence
includes the whole name i.e foo.cc in $(OBJS). When I do a make realclean,
boom... All my source files are deleted. But for Emacs I would have screwed.

I know this seems more of a pilot error but shouldn't make do something to
help the user ? Specifically is there any way in GNU Make to specify that
if a pattern substitute fails to replace anything, return null.

If I understand what Make does now, it tries to match the longest entry for
% and ends up matching the whole name but still doesn't find .cc and hence
doesn't perform the replace. But the problem arises because Make returns the
whole % at this point even if no match requested was found.

If it's not possible to change the semantics (legacy reasons et al, though
I don't know if anybody will really want this behaviour), will it be
possible to issue a warning option if a variable pattern substitution
results in a value which is the same as the original variable ? Even
something that detects such a thing in only this specified syntactic usage
is also very welcome.

More info on environment:

samba> uname -a
Linux samba 2.4.17 #2 SMP Fri Feb 15 21:32:35 CST 2002 i686 unknown

samba> make -v
GNU Make version 3.79.1, by Richard Stallman and Roland McGrath.
Built for i586-pc-linux-gnu
Copyright (C) 1988, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 2000
        Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

Report bugs to <address@hidden>.

samba> dpkg -p make
Package: make
Priority: standard
Section: devel
Installed-Size: 784
Maintainer: Manoj Srivastava <address@hidden>
Architecture: i386
Version: 3.79.1-12
Depends: libc6 (>= 2.2.4-4), fileutils (>= 4.0)
Filename: pool/main/m/make/make_3.79.1-11_i386.deb
Size: 386308
MD5sum: 5606dee81b90629a54771b8963461f44
Description: The GNU version of the "make" utility.
 GNU Make is a program that determines which pieces of a large
 program need to be recompiled and issues the commands to recompile
 them, when necessary. More information about GNU Make can be
 found in the `make' Info page. The upstream sources for this package
 are available at the location ftp://ftp.gnu.org/gnu/make/

-kitty.

-- 
Krishnakumar B <kitty at cs dot wustl dot edu>
Distributed Object Computing Laboratory, Washington University in St.Louis