* Use /tmp/nix-build-<drvpath>-<counter> instead of

  /tmp/nix-<pid>-<counter> for temporary build directories.  This
  increases purity a bit: many packages store the temporary build path
  in their output, causing (generally unimportant) binary differences.

3 files changed, 17 insertions, 8 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index a4f9c469c..e6ab6310c 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1568,7 +1568,7 @@ void DerivationGoal::startBuilder()
 
     /* Create a temporary directory where the build will take
        place. */
-    tmpDir = createTempDir();
+    tmpDir = createTempDir("", "nix-build-" + baseNameOf(drvPath), false, false);
 
     /* For convenience, set an environment pointing to the top build
        directory. */
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index d0731c0b4..822c87a05 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -318,19 +318,27 @@ void makePathReadOnly(const Path & path)
 }
 
 
-static Path tempName(const Path & tmpRoot, const Path & prefix)
+static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
+    int & counter)
 {
-    static int counter = 0;
-    Path tmpRoot2 = canonPath(tmpRoot.empty() ? getEnv("TMPDIR", "/tmp") : tmpRoot, true);
-    return (format("%1%/%2%-%3%-%4%") % tmpRoot2 % prefix % getpid() % counter++).str();
+    tmpRoot = canonPath(tmpRoot.empty() ? getEnv("TMPDIR", "/tmp") : tmpRoot, true);
+    if (includePid)
+        return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++).str();
+    else
+        return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
 }
 
 
-Path createTempDir(const Path & tmpRoot, const Path & prefix)
+Path createTempDir(const Path & tmpRoot, const Path & prefix,
+    bool includePid, bool useGlobalCounter)
 {
+    static int globalCounter = 0;
+    int localCounter = 0;
+    int & counter(useGlobalCounter ? globalCounter : localCounter);
+    
     while (1) {
         checkInterrupt();
-	Path tmpDir = tempName(tmpRoot, prefix);
+	Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
 	if (mkdir(tmpDir.c_str(), 0777) == 0) {
 	    /* Explicitly set the group of the directory.  This is to
 	       work around around problems caused by BSD's group
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 657f45ced..d75002b02 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -70,7 +70,8 @@ void deletePath(const Path & path, unsigned long long & bytesFreed);
 void makePathReadOnly(const Path & path);
 
 /* Create a temporary directory. */
-Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix");
+Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
+    bool includePid = true, bool useGlobalCounter = true);
 
 /* Create a directory and all its parents, if necessary.  Returns the
    list of created directories, in order of creation. */