* Automatically determine header file dependencies using the

`findIncludes' function.  The current implementation is impure and
  therefore not correct: it gathers header file dependencies only once
  for a specific path (due to caching).

examples/not-so-simple-header-auto/bar/hello.h

@@ -0,0 +1 @@
+#define WHAT "World"

examples/not-so-simple-header-auto/default.nix

@@ -0,0 +1,11 @@
+let {
+
+  inherit (import ../../lib) compileC findIncludes link;
+
+  hello = link {programName = "hello"; objects = compileC {
+    main = ./foo/hello.c;
+    localIncludes = import (findIncludes {main = toString ./foo/hello.c;});
+  };};
+
+  body = [hello];
+}

examples/not-so-simple-header-auto/foo/fnord/indirect.h

@@ -0,0 +1,3 @@
+#define HELLO "Hello"
+
+#include "../../bar/hello.h"

examples/not-so-simple-header-auto/foo/hello.c

@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#include "fnord/indirect.h"
+
+int main(int argc, char * * argv)
+{
+    printf(HELLO " " WHAT "\n");
+    return 0;
+}

lib/compile-c.sh

@@ -64,7 +64,9 @@ for ((n = 0; n < ${#localIncludes[*]}; n += 2)); do
 done
 
 # Create a symlink to the main file.
-ln -s $main $prefix$mainName
+if ! test "$(readlink $prefix$mainName)" = $main; then
+    ln -s $main $prefix$mainName
+fi
 
 mkdir $out
 test "$prefix" && cd $prefix

lib/default.nix

@@ -8,10 +8,24 @@ rec {
     inherit main localIncludes;
   };
 
+  /*
+  runCommand = {command}: {
+    name = "run-command";
+    builder = ./run-command.sh;
+    inherit command;
+  };
+  */
+
+  findIncludes = {main}: stdenv.mkDerivation {
+    name = "find-includes";
+    builder = ./find-includes.sh;
+    inherit main;
+  };
+  
   link = {objects, programName ? "program"}: stdenv.mkDerivation {
     name = "link";
     builder = ./link.sh;
     inherit objects programName;
   };
-  
+
 }

lib/find-includes.sh

@@ -0,0 +1,20 @@
+. $stdenv/setup
+
+echo "finding includes of \`$(basename $main)'..."
+
+makefile=$NIX_BUILD_TOP/makefile
+
+mainDir=$(dirname $main)
+(cd $mainDir && gcc -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