From 2e99159b7eccdac8407f59b236eb946bee88af3a 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 10 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 f292f06bb81..edae48aa71c 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -791,6 +791,25 @@ void NixRepl::addAttrsToScope(Value & attrs)
     staticEnv->sort();
     staticEnv->deduplicate();
     notice("Added %1% variables.", attrs.attrs()->size());
+
+    const int max_print = 10;
+    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 59d1f1be02a..bcd3313984f 100755
--- a/tests/functional/repl.sh
+++ b/tests/functional/repl.sh
@@ -153,6 +153,32 @@ 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: { ${builtins.toString x} = x; }) (builtins.genList (x: x) 13))
+' 'Added 13 variables.
+"0", "1", "10", "11", "12", "2", "3", "4", "5", "6"
+... and 3 more'
+
 # Test the `:reload` mechansim with flakes:
 # - Eval `./flake#changingThing`
 # - Modify the flake
@@ -301,7 +327,8 @@ runRepl () {
       -e "s@$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' \
     ;
 }