* Put the garbage collector in nix-store: operation `--gc',

  suboperations `--print-live', `--print-dead', and `--delete'.  The
  roots are not determined by nix-store; they are read from standard
  input.  This is to make it easy to customise what the roots are.

  The collector now no longer fails when store expressions are missing
  (which legally happens when using substitutes).  It never tries to
  fetch paths through substitutes.

  TODO: acquire a global lock on the store while garbage collecting.
  
* Removed `nix-store --delete'.

1 files changed, 57 insertions, 13 deletions

diff --git a/src/nix-store/main.cc b/src/nix-store/main.cc
index e83f9133f..78599e308 100644
--- a/src/nix-store/main.cc
+++ b/src/nix-store/main.cc
@@ -3,6 +3,7 @@
 
 #include "globals.hh"
 #include "normalise.hh"
+#include "gc.hh"
 #include "archive.hh"
 #include "shared.hh"
 #include "dotgraph.hh"
@@ -32,17 +33,6 @@ static void opRealise(Strings opFlags, Strings opArgs)
 }
 
 
-/* Delete a path in the Nix store directory. */
-static void opDelete(Strings opFlags, Strings opArgs)
-{
-    if (!opFlags.empty()) throw UsageError("unknown flag");
-
-    for (Strings::iterator it = opArgs.begin();
-         it != opArgs.end(); it++)
-        deleteFromStore(*it);
-}
-
-
 /* Add paths to the Nix values directory and print the hashes of those
    paths. */
 static void opAdd(Strings opFlags, Strings opArgs)
@@ -220,6 +210,60 @@ static void opIsValid(Strings opFlags, Strings opArgs)
 }
 
 
+static void opGC(Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() != 1) throw UsageError("missing flag");
+    if (!opArgs.empty())
+        throw UsageError("no arguments expected");
+
+    /* Do what? */
+    string flag = opFlags.front();
+    enum { soPrintLive, soPrintDead, soDelete } subOp;
+    if (flag == "--print-live") subOp = soPrintLive;
+    else if (flag == "--print-dead") subOp = soPrintDead;
+    else if (flag == "--delete") subOp = soDelete;
+    else throw UsageError(format("bad sub-operation `%1% in GC") % flag);
+        
+    Paths roots;
+    while (1) {
+        Path root;
+        getline(cin, root);
+        if (cin.eof()) break;
+        roots.push_back(root);
+    }
+
+    PathSet live = findLivePaths(roots);
+
+    if (subOp == soPrintLive) {
+        for (PathSet::iterator i = live.begin(); i != live.end(); ++i)
+            cout << *i << endl;
+        return;
+    }
+
+    PathSet dead = findDeadPaths(live);
+
+    if (subOp == soPrintDead) {
+        for (PathSet::iterator i = dead.begin(); i != dead.end(); ++i)
+            cout << *i << endl;
+        return;
+    }
+
+    if (subOp == soDelete) {
+
+        /* !!! What happens if the garbage collector run is aborted
+           halfway through?  In particular, dead paths can always
+           become live again (through re-instantiation), and might
+           then refer to deleted paths. => check instantiation
+           invariants */
+
+        for (PathSet::iterator i = dead.begin(); i != dead.end(); ++i) {
+            printMsg(lvlInfo, format("deleting `%1%'") % *i);
+            deleteFromStore(*i);
+        }
+    }
+}
+
+
 /* A sink that writes dump output to stdout. */
 struct StdoutSink : DumpSink
 {
@@ -298,8 +342,6 @@ void run(Strings args)
 
         if (arg == "--realise" || arg == "-r")
             op = opRealise;
-        else if (arg == "--delete" || arg == "-d")
-            op = opDelete;
         else if (arg == "--add" || arg == "-A")
             op = opAdd;
         else if (arg == "--query" || arg == "-q")
@@ -312,6 +354,8 @@ void run(Strings args)
             op = opValidPath;
         else if (arg == "--isvalid")
             op = opIsValid;
+        else if (arg == "--gc")
+            op = opGC;
         else if (arg == "--dump")
             op = opDump;
         else if (arg == "--restore")