* An quick and dirty hack to support distributed builds.

src/libmain/shared.cc

@@ -52,13 +52,6 @@ void checkStoreNotSymlink(Path path)
 }
 
 
-static string getEnv(const string & key, const string & def = "")
-{
-    char * value = getenv(key.c_str());
-    return value ? string(value) : def;
-}
-
-
 /* Initialize and reorder arguments, then call the actual argument
    processor. */
 static void initAndRun(int argc, char * * argv)

src/libstore/normalise.cc

@@ -302,6 +302,7 @@ bool Normaliser::startBuild(Path nePath)
 
     /* Obtain locks on all output paths.  The locks are automatically
        released when we exit this function or Nix crashes. */
+    /* !!! BUG: this could block, which is not allowed. */
     goal.outputLocks.lockPaths(goal.expr.derivation.outputs);
 
     /* Now check again whether there is a successor.  This is because
@@ -364,6 +365,25 @@ bool Normaliser::startBuild(Path nePath)
         return true;
     }
 
+    /* !!! Hack */
+    Path buildHook = getEnv("NIX_BUILD_HOOK");
+    if (buildHook != "") {
+        printMsg(lvlChatty, format("using build hook `%1%'") % buildHook);
+        int status = system((buildHook + " " + goal.nePath + " 1>&2").c_str());
+        if (WIFEXITED(status)) {
+            int code = WEXITSTATUS(status);
+            if (code == 100) { /* == accepted */
+                printMsg(lvlChatty,
+                    format("build hook succesfully realised output paths"));
+                finishGoal(goal);
+                return true;
+            } else if (code != 101) /* != declined */
+                throw Error(
+                    format("build hook returned exit code %1%") % code);
+        } else throw Error(
+            format("build hook died with status %1%") % status);
+    }
+
     /* Otherwise, start the build in a child process. */
     startBuildChild(goal);
 
@@ -660,7 +680,7 @@ void Normaliser::finishGoal(Goal & goal)
     {
         Path path = *i;
         if (!pathExists(path))
-            throw Error(format("path `%1%' does not exist") % path);
+            throw Error(format("output path `%1%' does not exist") % path);
         nf.closure.roots.insert(path);
 
 	makePathReadOnly(path);

src/libutil/util.cc

@@ -29,6 +29,13 @@ SysError::SysError(const format & f)
 }
 
 
+string getEnv(const string & key, const string & def)
+{
+    char * value = getenv(key.c_str());
+    return value ? string(value) : def;
+}
+
+
 Path absPath(Path path, Path dir)
 {
     if (path[0] != '/') {
@@ -206,8 +213,7 @@ void makePathReadOnly(const Path & path)
 static Path tempName()
 {
     static int counter = 0;
-    char * s = getenv("TMPDIR");
-    Path tmpRoot = s ? canonPath(Path(s)) : "/tmp";
+    Path tmpRoot = canonPath(getEnv("TMPDIR", "/tmp"));
     return (format("%1%/nix-%2%-%3%") % tmpRoot % getpid() % counter++).str();
 }
 

src/libutil/util.hh

@@ -55,6 +55,9 @@ typedef set<Path> PathSet;
 extern string thisSystem;
 
 
+/* Return an environment variable. */
+string getEnv(const string & key, const string & def = "");
+
 /* Return an absolutized path, resolving paths relative to the
    specified directory, or the current directory otherwise.  The path
    is also canonicalised. */

src/nix-env/main.cc

@@ -118,7 +118,7 @@ void loadDerivations(EvalState & state, Path nePath, DrvInfos & drvs)
 
 static Path getHomeDir()
 {
-    Path homeDir(getenv("HOME"));
+    Path homeDir(getEnv("HOME", ""));
     if (homeDir == "") throw Error("HOME environment variable not set");
     return homeDir;
 }