Merge pull request #8817 from iFreilicht/flake-update-lock-overhaul

Overhaul `nix flake update` and `nix flake lock` UX

(cherry picked from commit 12a0ae73dbb37becefa5a442eb4532ff0de9ce65)
Change-Id: Iff3b4f4235ebb1948ec612036b39ab29e4ca22b2

2 files changed, 25 insertions, 2 deletions

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 77069c7b9..3e39b4d7c 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -255,7 +255,18 @@ bool Args::processArgs(const Strings & args, bool finish)
         }
         if (!anyCompleted)
             exp.handler.fun(ss);
-        expectedArgs.pop_front();
+
+        /* Move the list element to the processedArgs. This is almost the same as
+           `processedArgs.push_back(expectedArgs.front()); expectedArgs.pop_front()`,
+           except that it will only adjust the next and prev pointers of the list
+           elements, meaning the actual contents don't move in memory. This is
+           critical to prevent invalidating internal pointers! */
+        processedArgs.splice(
+            processedArgs.end(),
+            expectedArgs,
+            expectedArgs.begin(),
+            ++expectedArgs.begin());
+
         res = true;
     }
 
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index c90a48ad4..77f7ff2a8 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -200,13 +200,25 @@ protected:
     /**
      * Queue of expected positional argument forms.
      *
-     * Positional arugment descriptions are inserted on the back.
+     * Positional argument descriptions are inserted on the back.
      *
      * As positional arguments are passed, these are popped from the
      * front, until there are hopefully none left as all args that were
      * expected in fact were passed.
      */
     std::list<ExpectedArg> expectedArgs;
+    /**
+     * List of processed positional argument forms.
+     *
+     * All items removed from `expectedArgs` are added here. After all
+     * arguments were processed, this list should be exactly the same as
+     * `expectedArgs` was before.
+     *
+     * This list is used to extend the lifetime of the argument forms.
+     * If this is not done, some closures that reference the command
+     * itself will segfault.
+    */
+   std::list<ExpectedArg> processedArgs;
 
     /**
      * Process some positional arugments