* Operation `--delete-generations' to delete generations of a

profile.  Arguments are either generation number, or `old' to delete
  all non-current generations.  Typical use:

  $ nix-env --delete-generations old
  $ nix-collect-garbage

* istringstream -> string2Int.

src/nix-env/main.cc

@@ -643,10 +643,8 @@ static void opSwitchGeneration(Globals & globals,
     if (opArgs.size() != 1)
         throw UsageError(format("exactly one argument expected"));
 
-    istringstream str(opArgs.front());
     int dstGen;
-    str >> dstGen;
-    if (!str || !str.eof())
+    if (!string2Int(opArgs.front(), dstGen))
         throw UsageError(format("expected a generation number"));
 
     switchGeneration(globals, dstGen);
@@ -688,6 +686,49 @@ static void opListGenerations(Globals & globals,
 }
 
 
+static void deleteGeneration2(const Path & profile, unsigned int gen)
+{
+    printMsg(lvlInfo, format("removing generation %1%") % gen);
+    deleteGeneration(profile, gen);
+}
+
+
+static void opDeleteGenerations(Globals & globals,
+    Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+
+    int curGen;
+    Generations gens = findGenerations(globals.profile, curGen);
+
+    for (Strings::iterator i = opArgs.begin(); i != opArgs.end(); ++i) {
+
+        if (*i == "old") {
+            for (Generations::iterator j = gens.begin(); j != gens.end(); ++j)
+                if (j->number != curGen)
+                    deleteGeneration2(globals.profile, j->number);
+        }
+
+        else {
+            int n;
+            if (!string2Int(*i, n) || n < 0)
+                throw UsageError(format("invalid generation specifier `%1%'")  % *i);
+            bool found = false;
+            for (Generations::iterator j = gens.begin(); j != gens.end(); ++j) {
+                if (j->number == n) {
+                    deleteGeneration2(globals.profile, j->number);
+                    found = true;
+                    break;
+                }
+            }
+            if (!found)
+                printMsg(lvlError, format("generation %1% does not exist") % n);
+        }
+    }
+}
+
+
 static void opDefaultExpr(Globals & globals,
     Strings opFlags, Strings opArgs)
 {
@@ -750,6 +791,8 @@ void run(Strings args)
             op = opRollback;
         else if (arg == "--list-generations")
             op = opListGenerations;
+        else if (arg == "--delete-generations")
+            op = opDeleteGenerations;
         else if (arg == "--dry-run") {
             printMsg(lvlInfo, "(dry run; not doing anything)");
             globals.dryRun = true;

src/nix-env/names.cc

@@ -56,20 +56,10 @@ static string nextComponent(string::const_iterator & p,
 }
 
 
-#include <fstream>
-
-static bool parseInt(const string & s, int & n)
-{
-    istringstream st(s);
-    st >> n;
-    return !st.fail();
-}
-
-
 static bool componentsLT(const string & c1, const string & c2)
 {
     int n1, n2;
-    bool c1Num = parseInt(c1, n1), c2Num = parseInt(c2, n2);
+    bool c1Num = string2Int(c1, n1), c2Num = string2Int(c2, n2);
 
     if (c1Num && c2Num) return n1 < n2;
     else if (c1 == "" && c2Num) return true;

src/nix-env/profiles.cc

@@ -20,9 +20,11 @@ static int parseName(const string & profileName, const string & name)
     string s = string(name, profileName.size() + 1);
     int p = s.find("-link");
     if (p == string::npos) return -1;
-    istringstream str(string(s, 0, p));
-    unsigned int n;
-    if (str >> n && str.eof()) return n; else return -1;
+    int n;
+    if (string2Int(string(s, 0, p), n) && n >= 0)
+        return n;
+    else
+        return -1;
 }
 
 
@@ -59,6 +61,16 @@ Generations findGenerations(Path profile, int & curGen)
 }
 
 
+static void makeNames(const Path & profile, unsigned int num,
+    Path & generation, Path & gcrootDrv, Path & gcrootClr)
+{
+    Path prefix = (format("%1%-%2%") % profile % num).str();
+    generation = prefix + "-link";
+    gcrootDrv = prefix + "-drv.gcroot";
+    gcrootClr = prefix + "-clr.gcroot";
+}
+
+
 Path createGeneration(Path profile, Path outPath,
     Path drvPath, Path clrPath)
 {
@@ -72,10 +84,7 @@ Path createGeneration(Path profile, Path outPath,
     Path generation, gcrootDrv, gcrootClr;
 
     while (1) {
-        Path prefix = (format("%1%-%2%") % profile % num).str();
-        generation = prefix + "-link";
-        gcrootDrv = prefix + "-drv.gcroot";
-        gcrootClr = prefix + "-clr.gcroot";
+        makeNames(profile, num, generation, gcrootDrv, gcrootClr);
         if (symlink(outPath.c_str(), generation.c_str()) == 0) break;
         if (errno != EEXIST)
             throw SysError(format("creating symlink `%1%'") % generation);
@@ -90,6 +99,23 @@ Path createGeneration(Path profile, Path outPath,
 }
 
 
+static void removeFile(const Path & path)
+{
+    if (remove(path.c_str()) == -1)
+        throw SysError(format("cannot unlink `%1%'") % path);
+}
+
+
+void deleteGeneration(const Path & profile, unsigned int gen)
+{
+    Path generation, gcrootDrv, gcrootClr;
+    makeNames(profile, gen, generation, gcrootDrv, gcrootClr);
+    removeFile(generation);
+    if (pathExists(gcrootClr)) removeFile(gcrootClr);
+    if (pathExists(gcrootDrv)) removeFile(gcrootDrv);
+}
+
+
 void switchLink(Path link, Path target)
 {
     /* Hacky. */

src/nix-env/profiles.hh

@@ -31,6 +31,8 @@ Generations findGenerations(Path profile, int & curGen);
 Path createGeneration(Path profile, Path outPath,
     Path drvPath, Path clrPath);
 
+void deleteGeneration(const Path & profile, unsigned int gen);
+
 void switchLink(Path link, Path target);