Mis-read Eelko's request to not make this an option: now, let's not make

it an option. :)

src/nix-env/nix-env.cc

@@ -58,7 +58,6 @@ struct Globals
     bool removeAll;
     string forceName;
     bool prebuiltOnly;
-    bool lazyGeneration;
 };
 
 
@@ -511,7 +510,7 @@ static void installDerivations(Globals & globals,
         if (globals.dryRun) return;
 
         if (createUserEnv(*globals.state, allElems,
-                profile, settings.envKeepDerivations, lockToken, globals.lazyGeneration)) break;
+                profile, settings.envKeepDerivations, lockToken)) break;
     }
 }
 
@@ -525,8 +524,6 @@ static void opInstall(Globals & globals, Strings opFlags, Strings opArgs)
             globals.preserveInstalled = true;
         else if (arg == "--remove-all" || arg == "-r")
             globals.removeAll = true;
-        else if (arg == "--lazy-generation")
-            globals.lazyGeneration = true;
         else throw UsageError(format("unknown flag ‘%1%’") % arg);
     }
 
@@ -620,7 +617,7 @@ static void upgradeDerivations(Globals & globals,
         if (globals.dryRun) return;
 
         if (createUserEnv(*globals.state, newElems,
-                globals.profile, settings.envKeepDerivations, lockToken, globals.lazyGeneration)) break;
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
     }
 }
 
@@ -684,7 +681,7 @@ static void opSetFlag(Globals & globals, Strings opFlags, Strings opArgs)
 
         /* Write the new user environment. */
         if (createUserEnv(*globals.state, installedElems,
-                globals.profile, settings.envKeepDerivations, lockToken, globals.lazyGeneration)) break;
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
     }
 }
 
@@ -721,8 +718,7 @@ static void opSet(Globals & globals, Strings opFlags, Strings opArgs)
     }
 
     debug(format("switching to new user environment"));
-    Path generation = createGeneration(globals.profile, drv.queryOutPath(),
-                                       globals.lazyGeneration);
+    Path generation = createGeneration(globals.profile, drv.queryOutPath());
     switchLink(globals.profile, generation);
 }
 
@@ -755,7 +751,7 @@ static void uninstallDerivations(Globals & globals, Strings & selectors,
         if (globals.dryRun) return;
 
         if (createUserEnv(*globals.state, newElems,
-                profile, settings.envKeepDerivations, lockToken, globals.lazyGeneration)) break;
+                profile, settings.envKeepDerivations, lockToken)) break;
     }
 }
 
@@ -1359,7 +1355,6 @@ int main(int argc, char * * argv)
         globals.preserveInstalled = false;
         globals.removeAll = false;
         globals.prebuiltOnly = false;
-        globals.lazyGeneration = false;
 
         parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
             Operation oldOp = op;

src/nix-env/profiles.cc

@@ -74,7 +74,7 @@ static void makeName(const Path & profile, unsigned int num,
 }
 
 
-Path createGeneration(Path profile, Path outPath, bool lazy)
+Path createGeneration(Path profile, Path outPath)
 {
     /* The new generation number should be higher than old the
        previous ones. */
@@ -85,9 +85,9 @@ Path createGeneration(Path profile, Path outPath, bool lazy)
     if (gens.size() > 0) {
         Generation last = gens.back();
 
-        if (lazy && readLink(last.path) == outPath) {
-            /* If lazy generations are enabled then we only create a 
-               new generation symlink if it differs from the last one.
+        if (readLink(last.path) == outPath) {
+            /* We only create a new generation symlink if it differs
+               from the last one.
 
                This helps keeping gratuitous installs/rebuilds from piling
                up uncontrolled numbers of generations, cluttering up the

src/nix-env/profiles.hh

@@ -31,7 +31,7 @@ typedef list<Generation> Generations;
    profile, sorted by generation number. */
 Generations findGenerations(Path profile, int & curGen);
     
-Path createGeneration(Path profile, Path outPath, bool lazy);
+Path createGeneration(Path profile, Path outPath);
 
 void deleteGeneration(const Path & profile, unsigned int gen);
 

src/nix-env/user-env.cc

@@ -28,7 +28,7 @@ DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
 
 bool createUserEnv(EvalState & state, DrvInfos & elems,
     const Path & profile, bool keepDerivations,
-    const string & lockToken, bool lazyGeneration)
+    const string & lockToken)
 {
     /* Build the components in the user environment, if they don't
        exist already. */
@@ -141,7 +141,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     }
 
     debug(format("switching to new user environment"));
-    Path generation = createGeneration(profile, topLevelOut, lazyGeneration);
+    Path generation = createGeneration(profile, topLevelOut);
     switchLink(profile, generation);
 
     return true;

src/nix-env/user-env.hh

@@ -8,6 +8,6 @@ DrvInfos queryInstalled(EvalState & state, const Path & userEnv);
 
 bool createUserEnv(EvalState & state, DrvInfos & elems,
     const Path & profile, bool keepDerivations,
-    const string & lockToken, bool lazyGeneration);
+    const string & lockToken);
 
 }

tests/user-envs.sh

@@ -99,25 +99,16 @@ if nix-env -q '*' | grep -q bar; then false; fi
 nix-env --list-generations
 test "$(nix-env --list-generations | wc -l)" -eq 7
 
-# Doing the same operation twice results in the same generation, but creates an
-# additional one. At this point we just brought back foo.
+# Doing the same operation twice results in the same generation, which triggers
+# "lazy" behaviour and does not create a new symlink.
 
+nix-env -i foo
 nix-env -i foo
 
 # Count generations.
 nix-env --list-generations
 test "$(nix-env --list-generations | wc -l)" -eq 8
 
-# Now, doing that again but passing the --lazy-generations flag will not
-# create a new generation.
-
-nix-env -i foo --lazy-generation
-
-# Count generations.
-nix-env --list-generations
-test "$(nix-env --list-generations | wc -l)" -eq 8
-
-
 # Switch to a specified generation.
 nix-env --switch-generation 7
 [ "$(nix-store -q --resolve $profiles/test)" = "$oldGen" ]