* 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.

1 files changed, 11 insertions, 8 deletions

diff --git a/make/lib/default.nix b/make/lib/default.nix
index a9b17d2ced77..b2f26a936785 100644
--- a/make/lib/default.nix
+++ b/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 {