erlehmann_

  #!/bin/sh
  redo-ifchange $2.c
  strace -e stat,stat64,fstat,fstat64,lstat,lstat64 -f 2>&1 >/dev/null\
   gcc $2.c -o $3 -MD -MF $2.deps\
   |grep '1 ENOENT'\
   |grep '\.h'\
   |cut -d'"' -f2 2>/dev/null\
   >$2.deps_ne
  
  read d <$2.deps
  redo-ifchange ${d#*:}
  
  while read -r d_ne; do
   redo-ifcreate $d_ne
  done <$2.deps_ne
  
  chmod a+x $3

I think the compiler should output the necessary information. To quote Jonathan de Boyne Pollard [3]:

> As noted earlier, no C or C++ compiler currently generates any redo-ifcreate dependency information, only the redo-ifchange dependency information. This is a deficiency of the compilers rather than a deficiency of redo, though. That the introduction of a new higher-precedence header earlier on the include path will affect recompilation is a fact that almost all C/C++ build systems fail to account for.

> I have written, but not yet released, a C++ tool that is capable of generating both redo-ifchange information for included files and redo-ifcreate information for the places where included files were searched for but didn't exist, and thus where adding new (different) included files would change the output.

JdeBP, could you please release your tool under a free software license? I suspect it has fewer errors than the similar CMake approach [4].

Also, how does scons handle non-existence dependencies?

What would be a scons dependency graph for this C code?

  #include<stdio.h>
  main() {
   printf("hello, world\n");
   return 0;
  }

I wrote a blog post to show how to integrate dependency output for both dependency and non-existence dependency generation [2]. The game “Liberation Circuit” can be built with my redo implementation; you can output a dependency graph usable with Graphviz [4] using “redo-dot”.

There is only one other redo implementation that I would recommend, the one from Jonathan de Boyne Pollard [5], who rightly notices that compilers should output information about non-existence dependencies [6].

I would not recommend the redo implementation from Avery Pennarun [7], which is often referenced (and introduced me to the concept), mainly because it is not implemented well: It manages to be both larger and slower than my shell script implementation, yet the documentation says this about the sqlite dependency (classic case of premature optimization):

> I don't think we can reach the performance we want with dependency/build/lock information stored in plain text files

> Especially when using C or C++, often target files depend on nonexistent files as well, meaning that a target file should be rebuilt when a previosly nonexistent file is created: If the preprocessor includes /usr/include/stdio.h because it could not find /usr/local/include/stdio.h, the creation of the latter file should trigger a rebuild.

I did some research on the topic using the repository of the game Liberation Circuit [3] and my own redo implementation [4] … it turns out that a typical project in C or C++ has lots of non-existence dependencies. How do make users handle non-existence dependencies – except for always calling “make clean”?