nix flake update: Recreate the lock file

This is probably what most people expect it to do. Fixes #3781.

There is a new command 'nix flake lock' that has the old behaviour of
'nix flake update', i.e. it just adds missing lock file entries unless
overriden using --update-input.

6 files changed, 104 insertions, 43 deletions

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 75eb19d28..afed0670f 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -19,6 +19,14 @@ void Args::addFlag(Flag && flag_)
     if (flag->shortName) shortFlags[flag->shortName] = flag;
 }
 
+void Args::removeFlag(const std::string & longName)
+{
+    auto flag = longFlags.find(longName);
+    assert(flag != longFlags.end());
+    if (flag->second->shortName) shortFlags.erase(flag->second->shortName);
+    longFlags.erase(flag);
+}
+
 void Completions::add(std::string completion, std::string description)
 {
     assert(description.find('\n') == std::string::npos);
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 4721c21df..c08ba8abd 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -140,6 +140,8 @@ public:
 
     void addFlag(Flag && flag);
 
+    void removeFlag(const std::string & longName);
+
     void expectArgs(ExpectedArg && arg)
     {
         expectedArgs.emplace_back(std::move(arg));
diff --git a/src/nix/flake-lock.md b/src/nix/flake-lock.md
new file mode 100644
index 000000000..2af0ad81e
--- /dev/null
+++ b/src/nix/flake-lock.md
@@ -0,0 +1,38 @@
+R""(
+
+# Examples
+
+* Update the `nixpkgs` and `nix` inputs of the flake in the current
+  directory:
+
+  ```console
+  # nix flake lock --update-input nixpkgs --update-input nix
+  * Updated 'nix': 'github:NixOS/nix/9fab14adbc3810d5cc1f88672fde1eee4358405c' -> 'github:NixOS/nix/8927cba62f5afb33b01016d5c4f7f8b7d0adde3c'
+  * Updated 'nixpkgs': 'github:NixOS/nixpkgs/3d2d8f281a27d466fa54b469b5993f7dde198375' -> 'github:NixOS/nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293'
+  ```
+
+# Description
+
+This command updates the lock file of a flake (`flake.lock`) so that
+it contains a lock for every flake input specified in
+`flake.nix`. Existing lock file entries are not updated unless
+required by a flag such as `--update-input`.
+
+Note that every command that operates on a flake will also update the
+lock file if needed, and supports the same flags. Therefore,
+
+```console
+# nix flake lock --update-input nixpkgs
+# nix build
+```
+
+is equivalent to:
+
+```console
+# nix build --update-input nixpkgs
+```
+
+Thus, this command is only useful if you want to update the lock file
+separately from any other action such as building.
+
+)""
diff --git a/src/nix/flake-update.md b/src/nix/flake-update.md
index a2ffedd2a..03b50e38e 100644
--- a/src/nix/flake-update.md
+++ b/src/nix/flake-update.md
@@ -2,52 +2,33 @@ R""(
 
 # Examples
 
-* Update the `nixpkgs` and `nix` inputs of the flake in the current
-  directory:
-
-  ```console
-  # nix flake update --update-input nixpkgs --update-input nix
-  * Updated 'nix': 'github:NixOS/nix/9fab14adbc3810d5cc1f88672fde1eee4358405c' -> 'github:NixOS/nix/8927cba62f5afb33b01016d5c4f7f8b7d0adde3c'
-  * Updated 'nixpkgs': 'github:NixOS/nixpkgs/3d2d8f281a27d466fa54b469b5993f7dde198375' -> 'github:NixOS/nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293'
-  ```
-
 * Recreate the lock file (i.e. update all inputs) and commit the new
   lock file:
 
   ```console
-  # nix flake update --recreate-lock-file --commit-lock-file
+  # nix flake update
+  * Updated 'nix': 'github:NixOS/nix/9fab14adbc3810d5cc1f88672fde1eee4358405c' -> 'github:NixOS/nix/8927cba62f5afb33b01016d5c4f7f8b7d0adde3c'
+  * Updated 'nixpkgs': 'github:NixOS/nixpkgs/3d2d8f281a27d466fa54b469b5993f7dde198375' -> 'github:NixOS/nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293'
   …
   warning: committed new revision '158bcbd9d6cc08ab859c0810186c1beebc982aad'
   ```
 
 # Description
 
-This command updates the lock file of a flake (`flake.lock`) so that
-it contains a lock for every flake input specified in
-`flake.nix`. Note that every command that operates on a flake will
-also update the lock file if needed, and supports the same
-flags. Therefore,
+This command recreates the lock file of a flake (`flake.lock`), thus
+updating the lock for every mutable input (like `nixpkgs`) to its
+current version. This is equivalent to passing `--recreate-lock-file`
+to any command that operates on a flake. That is,
 
 ```console
-# nix flake update --update-input nixpkgs
+# nix flake update
 # nix build
 ```
 
 is equivalent to:
 
 ```console
-# nix build --update-input nixpkgs
+# nix build --recreate-lock-file
 ```
 
-Thus, this command is only useful if you want to update the lock file
-separately from any other action such as building.
-
-> **Note**
->
-> This command does *not* update locks that are already present unless
-> you explicitly ask for it using `--update-input` or
-> `--recreate-lock-file`. Thus, if the lock file already has locks for
-> every input, then `nix flake update` (without arguments) does
-> nothing.
-
 )""
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index b9cde5d6d..2f0c468a8 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -104,6 +104,14 @@ struct CmdFlakeUpdate : FlakeCommand
         return "update flake lock file";
     }
 
+    CmdFlakeUpdate()
+    {
+        /* Remove flags that don't make sense. */
+        removeFlag("recreate-lock-file");
+        removeFlag("update-input");
+        removeFlag("no-update-lock-file");
+    }
+
     std::string doc() override
     {
         return
@@ -113,7 +121,30 @@ struct CmdFlakeUpdate : FlakeCommand
 
     void run(nix::ref<nix::Store> store) override
     {
-        /* Use --refresh by default for 'nix flake update'. */
+        settings.tarballTtl = 0;
+
+        lockFlags.recreateLockFile = true;
+
+        lockFlake();
+    }
+};
+
+struct CmdFlakeLock : FlakeCommand
+{
+    std::string description() override
+    {
+        return "create missing lock file entries";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "flake-lock.md"
+          ;
+    }
+
+    void run(nix::ref<nix::Store> store) override
+    {
         settings.tarballTtl = 0;
 
         lockFlake();
@@ -1006,6 +1037,7 @@ struct CmdFlake : NixMultiCommand
     CmdFlake()
         : MultiCommand({
                 {"update", []() { return make_ref<CmdFlakeUpdate>(); }},
+                {"lock", []() { return make_ref<CmdFlakeLock>(); }},
                 {"info", []() { return make_ref<CmdFlakeInfo>(); }},
                 {"list-inputs", []() { return make_ref<CmdFlakeListInputs>(); }},
                 {"check", []() { return make_ref<CmdFlakeCheck>(); }},
diff --git a/tests/flakes.sh b/tests/flakes.sh
index 2b7bcdd68..25ba2ac43 100644
--- a/tests/flakes.sh
+++ b/tests/flakes.sh
@@ -232,7 +232,7 @@ nix build -o $TEST_ROOT/result --flake-registry file:///no-registry.json $flake2
 nix build -o $TEST_ROOT/result --no-registries $flake2Dir#bar --refresh
 
 # Updating the flake should not change the lockfile.
-nix flake update $flake2Dir
+nix flake lock $flake2Dir
 [[ -z $(git -C $flake2Dir diff master) ]]
 
 # Now we should be able to build the flake in pure mode.
@@ -354,10 +354,10 @@ nix build -o $TEST_ROOT/result flake3#xyzzy flake3#fnord
 nix build -o $TEST_ROOT/result flake4#xyzzy
 
 # Test 'nix flake update' and --override-flake.
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ -z $(git -C $flake3Dir diff master) ]]
 
-nix flake update $flake3Dir --recreate-lock-file --override-flake flake2 nixpkgs
+nix flake update $flake3Dir --override-flake flake2 nixpkgs
 [[ ! -z $(git -C $flake3Dir diff master) ]]
 
 # Make branch "removeXyzzy" where flake3 doesn't have xyzzy anymore
@@ -389,7 +389,7 @@ cat > $flake3Dir/flake.nix <<EOF
   };
 }
 EOF
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 git -C $flake3Dir add flake.nix flake.lock
 git -C $flake3Dir commit -m 'Remove packages.xyzzy'
 git -C $flake3Dir checkout master
@@ -547,7 +547,7 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ $(jq -c .nodes.root.inputs.bar $flake3Dir/flake.lock) = '["foo"]' ]]
 
 cat > $flake3Dir/flake.nix <<EOF
@@ -559,7 +559,7 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ $(jq -c .nodes.root.inputs.bar $flake3Dir/flake.lock) = '["flake2","flake1"]' ]]
 
 cat > $flake3Dir/flake.nix <<EOF
@@ -571,7 +571,7 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ $(jq -c .nodes.root.inputs.bar $flake3Dir/flake.lock) = '["flake2"]' ]]
 
 # Test overriding inputs of inputs.
@@ -587,7 +587,7 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ $(jq .nodes.flake1.locked.url $flake3Dir/flake.lock) =~ flake7 ]]
 
 cat > $flake3Dir/flake.nix <<EOF
@@ -600,7 +600,7 @@ cat > $flake3Dir/flake.nix <<EOF
 }
 EOF
 
-nix flake update $flake3Dir --recreate-lock-file
+nix flake update $flake3Dir
 [[ $(jq -c .nodes.flake2.inputs.flake1 $flake3Dir/flake.lock) =~ '["foo"]' ]]
 [[ $(jq .nodes.foo.locked.url $flake3Dir/flake.lock) =~ flake7 ]]
 
@@ -658,20 +658,20 @@ nix build -o $TEST_ROOT/result "file://$TEST_ROOT/flake.tar.gz?narHash=sha256-qQ
 
 # Test --override-input.
 git -C $flake3Dir reset --hard
-nix flake update $flake3Dir --override-input flake2/flake1 flake5 -vvvvv
+nix flake lock $flake3Dir --override-input flake2/flake1 flake5 -vvvvv
 [[ $(jq .nodes.flake1_2.locked.url $flake3Dir/flake.lock) =~ flake5 ]]
 
-nix flake update $flake3Dir --override-input flake2/flake1 flake1
+nix flake lock $flake3Dir --override-input flake2/flake1 flake1
 [[ $(jq -r .nodes.flake1_2.locked.rev $flake3Dir/flake.lock) =~ $hash2 ]]
 
-nix flake update $flake3Dir --override-input flake2/flake1 flake1/master/$hash1
+nix flake lock $flake3Dir --override-input flake2/flake1 flake1/master/$hash1
 [[ $(jq -r .nodes.flake1_2.locked.rev $flake3Dir/flake.lock) =~ $hash1 ]]
 
 # Test --update-input.
-nix flake update $flake3Dir
+nix flake lock $flake3Dir
 [[ $(jq -r .nodes.flake1_2.locked.rev $flake3Dir/flake.lock) = $hash1 ]]
 
-nix flake update $flake3Dir --update-input flake2/flake1
+nix flake lock $flake3Dir --update-input flake2/flake1
 [[ $(jq -r .nodes.flake1_2.locked.rev $flake3Dir/flake.lock) =~ $hash2 ]]
 
 # Test 'nix flake list-inputs'.