From 3c9b9b13af52776ca08bbbb12b3a98f45de6083b Mon Sep 17 00:00:00 2001
From: Kevin Robert Stravers <kevin@stravers.net>
Date: Sat, 21 Sep 2024 02:56:04 -0400
Subject: [PATCH] nix repl: Print which variables are just loaded

When we run `nix repl nixpkgs` we get "Added 6 variables". This is not
useful as it doesn't tell us which variables the flake has exported to
our global repl scope.

This patch prints the name of each variable that was just loaded. We
currently cap printing to 20 variables in order to avoid excessive
prints.

https://github.com/NixOS/nix/issues/11404
---
 src/libcmd/repl.cc       | 19 +++++++++++++++++++
 tests/functional/repl.sh | 29 ++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 07968fa43..e5164b137 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -813,6 +813,25 @@ void NixRepl::addAttrsToScope(Value & attrs)
     staticEnv->sort();
     staticEnv->deduplicate();
     notice("Added %1% variables.", attrs.attrs()->size());
+
+    const int max_print = 20;
+    int counter = 0;
+    std::ostringstream loaded;
+    for (auto & i : attrs.attrs()->lexicographicOrder(state->symbols)) {
+        if (counter >= max_print)
+            break;
+
+        if (counter > 0)
+            loaded << ", ";
+
+        printIdentifier(loaded, state->symbols[i->name]);
+        counter += 1;
+    }
+
+    notice("%1%", loaded.str());
+
+    if (attrs.attrs()->size() > max_print)
+        notice("... and %1% more", attrs.attrs()->size() - max_print);
 }
 
 
diff --git a/tests/functional/repl.sh b/tests/functional/repl.sh
index 762636e44..7f5b26913 100755
--- a/tests/functional/repl.sh
+++ b/tests/functional/repl.sh
@@ -157,6 +157,32 @@ foo + baz
 ' "3" \
     ./flake ./flake\#bar --experimental-features 'flakes'
 
+testReplResponse $'
+:a { a = 1; b = 2; longerName = 3; "with spaces" = 4; }
+' 'Added 4 variables.
+a, b, longerName, "with spaces"
+'
+
+cat <<EOF > attribute-set.nix
+{
+    a = 1;
+    b = 2;
+    longerName = 3;
+    "with spaces" = 4;
+}
+EOF
+testReplResponse '
+:l ./attribute-set.nix
+' 'Added 4 variables.
+a, b, longerName, "with spaces"
+'
+
+testReplResponseNoRegex $'
+:a builtins.foldl\' (x: y: x // y) {} (map (x: { ${builtins.toString x} = x; }) (builtins.genList (x: x) 23))
+' 'Added 23 variables.
+"0", "1", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "2", "20", "21", "22", "3", "4", "5", "6"
+... and 3 more'
+
 # Test the `:reload` mechansim with flakes:
 # - Eval `./flake#changingThing`
 # - Modify the flake
@@ -322,7 +348,8 @@ runRepl () {
       -e "s@$testDir@/path/to/tests/functional@g" \
       -e "s@$testDirNoUnderscores@/path/to/tests/functional@g" \
       -e "s@$nixVersion@<nix version>@g" \
-      -e "s@Added [0-9]* variables@Added <number omitted> variables@g" \
+      -e "/Added [0-9]* variables/{s@ [0-9]* @ <number omitted> @;n;d}" \
+      -e '/\.\.\. and [0-9]* more/d' \
     | grep -vF $'warning: you don\'t have Internet access; disabling some network-dependent features' \
     ;
 }