Features¶

Automatic scanning for include files

Makepp scans automatically for include files. This obviates the need for tools like makedepend. Makepp's scanner works even if the included files don't exist yet but have to be built. (This is true no matter where on the include path they come from, unlike programs that depend on gcc's "-MM -MG" option.) Makepp has a flexible system for doing this which is based on scanning the build command; you can adapt it for other languages or build commands by writing a Perl subroutine.

Better system for hierarchical builds

Makepp has a better system for handling builds involving multiple directories and multiple makefiles. The traditional technique is to have make invoke itself recursively in each directory. Depending on how complicated the interdependencies are, several recursive passes are sometimes needed. This makes the makefiles very complicated if they guarantee a correct build. The real problem is that unless dependencies are trivial (e.g., just one library file), it is almost impossible to express accurately dependencies of targets in one makefile in terms of targets from the other makefile. Unix make isn't smart enough to realize that a target in one makefile depends on a file that is a target in a lower-level makefile; it can't take build commands from the lower-level makefile while it is trying to build the target in the upper-level makefile. So the usual solution is to build everything that can be built with the lower-level makefiles, hoping that that's adequate to build everything that's needed for the upper-level makefile.

Makepp loads all the needed makefiles in at once, so it has no problem dealing with situations where a file from one makefile depends on a file produced by a different makefile. Makepp cd's automatically to the directory containing the makefile before executing a command from a makefile, so each makefile may be written independently without knowledge of the top-level build directory. But if access to the root of your build tree is important (e.g. because that's where your include directory resides), you can name the makefile in that directory specially. Then makepp gives you the path to that directory in a variable.

Makepp also can figure out where all the makefiles for the entire project are without being told, if each makefile is in the same directory as the files it is supposed to produce. This can also simplify makefiles a great deal.

For more details on building with multiple directories, see "Tips for multiple directories" in makepp_cookbook.

Reliable wildcards

Makefiles can use wildcards reliably, because wild cards match either files that exist, or files that do not yet exist but makepp knows how to build. So even for a program with dozens of modules, your entire makefile could simply read something like this:

    CXX = g++
    CXXFLAGS = -g
 
    %.o : %.c
        $(CXX) $(CXXFLAGS) -c $(input) -o $(output)
 
    my_program: *.o
        $(CXX) $(inputs) -o $(output)
    

and this will work even if none of the ".o" files have been built yet.

Reliable builds: remembers build command

Makepp keeps track of the build commands, so that if compilation options change, files are automatically rebuilt. This is important to guarantee correct builds. (This idea was taken from Bob Sidebothem's "cons" utility, which was described in the Perl Journal in 1998 and is available from CPAN.)

To illustrate why this is important, consider the following structure definition:

    class ABC {
      int x;
    #ifndef SPECIAL_OPTION
      int y;
    #endif
      int z;
    };
    

Now suppose you decide to turn on the "SPECIAL_OPTION" option by adding "-DSPECIAL_OPTION" to the command line. A recompilation of everything is needed, but a traditional Unix make will not detect this, and will only recompile source files which have actually changed. As a result, some of your modules will be compiled with -DSPECIAL_OPTION, and others won't. After a very frustrating debugging session, you will discover that all that needs to be done is to rebuild everything. Then you will curse make and hopefully switch to an improved implementation of it, like makepp. At least, that's what I did.

As another example, suppose that you are working on a project which is pretty well debugged, so it's usually compiled with "-O2". Now you run into a bug which you need to look at in the debugger. Code compiled with optimization is difficult to examine in the debugger, so you want to recompile your code so that you can look at it. If your makefile is set up to store the compiler options in the usual variables, you can just do this:

    makepp CFLAGS=-g CXXFLAGS=-g
    

and makepp will know that the command line has changed for all the modules. Then when you've found your bug, just type

    makepp
    

and it will be recompiled with optimization. You don't need to type "make clean" when you change build options.

Some makefiles (e.g., those for the Linux kernel) go to incredible lengths to force recompilation when the compile command changes. With makepp, it's taken care of automatically--you don't have to do anything.

Reliable builds: exact matching of signature

By default, makepp doesn't merely ensure that all targets are newer than all dependencies; if you replace a dependency with an older file, makepp knows that it has to rebuild the target, simply because the input file has changed. This is another important feature to guarantee correct builds which was taken from the "cons" utility.

Smart signature calculations

Some modifications to source files do not actually require a rebuild. For example, if you just change a comment line, or if you reindent some code, there is no particular reason to force a compilation. For C/C++ compilation, makepp determines whether a file needs recompilation by computing a cryptographic checksum of the file's contents, ignoring comments and whitespace, instead of looking at the file time.

This is particularly useful if you have include files that are generated by files that change, and yet the generated include files themselves seldom change. Suppose you have a complicated yacc grammar in your program, with a build rule like this:

    y.tab.c y.tab.h: parser.y
        yacc -d parser.y
    

Ordinarily, every time you make even a tiny change to "parser.y", every file that depends on "y.tab.h" must be rebuilt since the file time of "y.tab.h" has changed. However, most changes to "parser.y" won't actually change the contents of "y.tab.h" (except possibly a comment), so all that recompilation is unnecessary.

Repositories

Makepp can automatically incorporate files from a different directory tree (the "repository") into the current build tree as needed. (This idea was also taken from the "cons" program.) This has several interesting uses:

Automatic inference of needed ".o" files

Makepp can often infer exactly which objects are actually necessary without being explicitly told. If you use this feature, then if one of your source file includes "xx.h", and there is a file called "xx.o" that makepp knows how to make, then makepp adds "xx.o" to the link command line. I don't use non-shared libraries now in many places where I used to, because makepp can automatically pick out the modules I need.

Correct handling of aliases for directories

Makepp won't be confused by soft links to a directory or by different relative filenames that refer to the same file. All directory paths to a file are recognized, including foo, ./foo, ../src/foo, /auto_mnt/somedisk/bob/src/foo, and /users/bob/src/foo.

Filenames with special characters

Makepp can support filenames with colons or spaces or other special characters that cause trouble for the traditional make. Just surround the filename with quotes. (See "Special characters" in makepp_rules for details.)

Extensible textual substutition functions

Makepp can use arbitrary Perl subroutines for textual substitution in the makefile. If you know Perl, you are not constrained at all by the set of makepp's builtin textual manipulation functions.

You can also simply write Perl code in your makefile. You can manipulate Make variables with the full power of the entire Perl language. See makepp_variables for details.

Logging of build decisions

By default, makepp makes a log-file viewable with makepplog, mppl that contains a description of every file that it tried to build, what rule was used to build it, what it depended on, and (if the file was rebuilt) why. This can be extremely useful for debugging a makefile--if you're wondering why makepp decided to rebuild a file, or why it didn't, you can just look in the log file where it explains the decisions.

Improved support for parallel builds

Makepp supports parallel compilations, but (unlike other make implementations) it won't mix output from separate processes which are running simultaneously.

Synonyms for cryptic variables

Makepp supports easier-to-remember synonyms for the cryptic make variables $@, $^, and $<. See makepp_variables for details.