nix flake metadata: print modified dates for input flakes

This was always in the lock file and we can simply actually print it.

The test for this is a little bit silly but it should correctly
control for my daring to exercise timezone code *and* locale code in a
test, which I strongly suspect nobody dared do before.

Sample (abridged):
```
Path:          /nix/store/gaxb42z68bcr8lch467shvmnhjjzgd8b-source
Last modified: 1970-01-01 00:16:40
Inputs:
├───flake-compat: github:edolstra/flake-compat/0f9255e01c2351cc7d116c072cb317785dd33b33
│   Last modified: 2023-10-04 13:37:54
├───flake-utils: github:numtide/flake-utils/b1d9ab70662946ef0850d488da1c9019f3a9752a
│   Last modified: 2024-03-11 08:33:50
│   └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
│       Last modified: 2023-04-09 08:27:08
```

Change-Id: I355f82cb4b633974295375ebad646fb6e2107f9b

1 files changed, 19 insertions, 5 deletions

diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 9d18b81b8..672930342 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -209,6 +209,11 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
     {
         auto lockedFlake = lockFlake();
         auto & flake = lockedFlake.flake;
+        auto formatTime = [](time_t time) -> std::string {
+            std::ostringstream os{};
+            os << std::put_time(std::localtime(&time), "%F %T");
+            return os.str();
+        };
 
         if (json) {
             nlohmann::json j;
@@ -260,7 +265,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
             if (auto lastModified = flake.lockedRef.input.getLastModified())
                 logger->cout(
                     ANSI_BOLD "Last modified:" ANSI_NORMAL " %s",
-                    std::put_time(std::localtime(&*lastModified), "%F %T"));
+                    formatTime(*lastModified));
 
             if (!lockedFlake.lockFile.root->inputs.empty())
                 logger->cout(ANSI_BOLD "Inputs:" ANSI_NORMAL);
@@ -275,16 +280,25 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                     bool last = i + 1 == node.inputs.size();
 
                     if (auto lockedNode = std::get_if<0>(&input.second)) {
-                        logger->cout("%s" ANSI_BOLD "%s" ANSI_NORMAL ": %s",
-                            prefix + (last ? treeLast : treeConn), input.first,
+                        // ├───agenix: github:ryantm/agenix/8d37c5bdeade12b6479c85acd133063ab53187a0
+                        logger->cout("%s%s" ANSI_BOLD "%s" ANSI_NORMAL ": %s",
+                            prefix, last ? treeLast : treeConn, input.first,
                             (*lockedNode)->lockedRef);
 
+                        // ├───lix: https://git.lix.systems/api/v1/repos/lix-project <....>
+                        // │   Last modified: 2024-07-31 21:01:34
+                        if (auto lastModified = (*lockedNode)->lockedRef.input.getLastModified()) {
+                            logger->cout("%s%s" ANSI_BOLD "%s" ANSI_NORMAL ": %s",
+                                prefix, last ? treeNull : treeLine, "Last modified", formatTime(*lastModified));
+                        }
+
                         bool firstVisit = visited.insert(*lockedNode).second;
 
                         if (firstVisit) recurse(**lockedNode, prefix + (last ? treeNull : treeLine));
                     } else if (auto follows = std::get_if<1>(&input.second)) {
-                        logger->cout("%s" ANSI_BOLD "%s" ANSI_NORMAL " follows input '%s'",
-                            prefix + (last ? treeLast : treeConn), input.first,
+                        // │   ├───darwin follows input 'flake-utils'
+                        logger->cout("%s%s" ANSI_BOLD "%s" ANSI_NORMAL " follows input '%s'",
+                            prefix, last ? treeLast : treeConn, input.first,
                             printInputPath(*follows));
                     }
                 }