* A primitive operation `dependencyClosure' to do automatic dependency

determination (e.g., finding the header files dependencies of a C
  file) in Nix low-level builds automatically.

  For instance, in the function `compileC' in make/lib/default.nix, we
  find the header file dependencies of C file `main' as follows:

    localIncludes =
      dependencyClosure {
        scanner = file:
          import (findIncludes {
            inherit file;
          });
        startSet = [main];
      };

  The function works by "growing" the set of dependencies, starting
  with the set `startSet', and calling the function `scanner' for each
  file to get its dependencies (which should yield a list of strings
  representing relative paths).  For instance, when `scanner' is
  called on a file `foo.c' that includes the line

    #include "../bar/fnord.h"

  then `scanner' should yield ["../bar/fnord.h"].  This list of
  dependencies is absolutised relative to the including file and added
  to the set of dependencies.  The process continues until no more
  dependencies are found (hence its a closure).

  `dependencyClosure' yields a list that contains in alternation a
  dependency, and its relative path to the directory of the start
  file, e.g.,

    [ /bla/bla/foo.c
      "foo.c"
      /bla/bar/fnord.h
      "../bar/fnord.h"
    ]

  These relative paths are necessary for the builder that compiles
  foo.c to reconstruct the relative directory structure expected by
  foo.c.

  The advantage of `dependencyClosure' over the old approach (using
  the impure `__currentTime') is that it's completely pure, and more
  efficient because it only rescans for dependencies (i.e., by
  building the derivations yielded by `scanner') if sources have
  actually changed.  The old approach rescanned every time.

make/lib/compile-c.sh

@@ -70,4 +70,5 @@ fi
 
 mkdir $out
 test "$prefix" && cd $prefix
+ls -l
 gcc -Wall $cFlags -c $mainName -o $out/$mainName.o

make/lib/default.nix

@@ -14,11 +14,13 @@ rec {
     builder = ./compile-c.sh;
     localIncludes =
       if localIncludes == "auto" then
-        import (findIncludes {
-          main = toString main;
-          hack = __currentTime;
-          inherit cFlags;
-        })
+        dependencyClosure {
+          scanner = main:
+            import (findIncludes {
+              inherit main;
+            });
+          startSet = [main];
+        }
       else
         localIncludes;
     inherit main;
@@ -36,10 +38,11 @@ rec {
   };
   */
 
-  findIncludes = {main, hack, cFlags ? ""}: stdenv.mkDerivation {
+  findIncludes = {main}: stdenv.mkDerivation {
     name = "find-includes";
-    builder = ./find-includes.sh;
-    inherit main hack cFlags;
+    realBuilder = pkgs.perl ~ "bin/perl";
+    args = [ ./find-includes.pl ];
+    inherit main;
   };
   
   link = {objects, programName ? "program", libraries ? []}: stdenv.mkDerivation {

make/lib/find-includes.pl

@@ -0,0 +1,19 @@
+use strict;
+
+my $root = $ENV{"main"};
+my $out = $ENV{"out"};
+
+open OUT, ">$out" or die "$!";
+print OUT "[\n";
+
+open IN, "<$root" or die "$!";
+while (<IN>) {
+    if (/^\#include\s+\"(.*)\"/) {
+        print "DEP $1\n";
+        print OUT "\"$1\"\n";
+    }
+}
+close IN;
+
+print OUT "]\n";
+close OUT;

make/lib/find-includes.sh

@@ -1,20 +0,0 @@
-. $stdenv/setup
-
-echo "finding includes of \`$(basename $main)'..."
-
-makefile=$NIX_BUILD_TOP/makefile
-
-mainDir=$(dirname $main)
-(cd $mainDir && gcc $cFlags -MM $(basename $main) -MF $makefile) || false
-
-echo "[" >$out
-
-while read line; do
-    line=$(echo "$line" | sed 's/.*://')
-    for i in $line; do
-        fullPath=$(readlink -f $mainDir/$i)
-        echo "  [ $fullPath \"$i\" ]" >>$out
-    done
-done < $makefile
-
-echo "]" >>$out