* Deal with directory components in header file references (e.g.,

`#include "foo/../bar/bla.h"') by building an appropriate tree of
  symlinks.

examples/default.nix

@@ -1,3 +1,4 @@
 [ (import ./trivial)
   (import ./simple-header)
+  (import ./not-so-simple-header)
 ]

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

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

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

@@ -0,0 +1,14 @@
+let {
+
+  inherit (import ../../lib) compileC link;
+
+  hello = link {objects = compileC {
+    main = ./foo/hello.c;
+    localIncludes = [
+      [./foo/fnord/indirect.h "fnord/indirect.h"]
+      [./bar/hello.h "fnord/../../bar/hello.h"]
+    ];
+  };};
+
+  body = [hello];
+}

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

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

examples/not-so-simple-header/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

@@ -1,18 +1,70 @@
 . $stdenv/setup
 
 mainName=$(basename $main | cut -c34-)
-ln -s $main $mainName
 
 echo "compiling $mainName..."
 
+# Turn $localIncludes into an array.
 localIncludes=($localIncludes)
+
+# Determine how many `..' levels appear in the header file references.
+# E.g., if there is some reference `../../foo.h', then we have to
+# insert two extra levels in the directory structure, so that `a.c' is
+# stored at `dotdot/dotdot/a.c', and a reference from it to
+# `../../foo.h' resolves to `dotdot/dotdot/../../foo.h' == `foo.h'.
 n=0
-while test $n -lt ${#localIncludes[*]}; do
-    source=${localIncludes[n]}
-    target=${localIncludes[$((n+1))]}
-    ln -s $source $target
-    n=$((n + 2))
+maxDepth=0
+for ((n = 0; n < ${#localIncludes[*]}; n += 2)); do
+    target=${localIncludes[$((n + 1))]}
+
+    # Split the target name into path components using some IFS magic.
+    savedIFS="$IFS"
+    IFS=/
+    components=($target)
+    depth=0
+    for ((m = 0; m < ${#components[*]}; m++)); do
+        c=${components[m]}
+        if test "$c" = ".."; then
+            depth=$((depth + 1))
+        fi
+    done
+    IFS="$savedIFS"
+
+    if test $depth -gt $maxDepth; then
+        maxDepth=$depth;
+    fi
 done
 
+# Create the extra levels in the directory hierarchy.
+prefix=
+for ((n = 0; n < maxDepth; n++)); do
+    prefix="dotdot/$prefix"
+done
+
+# Create symlinks to the header files.
+for ((n = 0; n < ${#localIncludes[*]}; n += 2)); do
+    source=${localIncludes[n]}
+    target=${localIncludes[$((n + 1))]}
+
+    # Create missing directories.  We use IFS magic to split the path
+    # into path components.
+    savedIFS="$IFS"
+    IFS=/
+    components=($prefix$target)
+    fullPath=(.)
+    for ((m = 0; m < ${#components[*]} - 1; m++)); do
+        fullPath=("${fullPath[@]}" ${components[m]})
+        if ! test -d "${fullPath[*]}"; then
+            mkdir "${fullPath[*]}"
+        fi
+    done
+    IFS="$savedIFS"
+    
+    ln -s $source $prefix$target
+done
+
+# Create a symlink to the main file.
+ln -s $main $prefix$mainName
+
 mkdir $out
-gcc -Wall -c $mainName -o $out/$mainName.o
+gcc -Wall -c $prefix$mainName -o $out/$mainName.o