From a5c969db496843b9a42b3aee494a02714ee9ca78 Mon Sep 17 00:00:00 2001
From: Artturin <Artturin@artturin.com>
Date: Wed, 16 Mar 2022 20:48:50 +0200
Subject: [PATCH 1/2] nix: allow using --file - to read from stdin

---
 doc/manual/src/release-notes/rl-next.md | 2 ++
 src/libcmd/installables.cc              | 9 +++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index c869b5e2f..c9753f9aa 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -1 +1,3 @@
 # Release X.Y (202?-??-??)
+
+* Various nix commands can now read expressions from stdin with `--file -`.
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index b7623d4ba..784117569 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -134,7 +134,9 @@ SourceExprCommand::SourceExprCommand()
     addFlag({
         .longName = "file",
         .shortName = 'f',
-        .description = "Interpret installables as attribute paths relative to the Nix expression stored in *file*.",
+        .description =
+            "Interpret installables as attribute paths relative to the Nix expression stored in *file*. "
+            "If *file* is the character -, then a Nix expression will be read from standard input.",
         .category = installablesCategory,
         .labels = {"file"},
         .handler = {&file},
@@ -695,7 +697,10 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         auto state = getEvalState();
         auto vFile = state->allocValue();
 
-        if (file)
+        if (file == "-") {
+            auto e = state->parseStdin();
+            state->eval(e, *vFile);
+        } else if (file)
             state->evalFile(lookupFileArg(*state, *file), *vFile);
         else {
             auto e = state->parseExprFromString(*expr, absPath("."));

From 4f8ad41d4eb2012f01cd09ad745e78c5b8d8bee6 Mon Sep 17 00:00:00 2001
From: Artturin <Artturin@artturin.com>
Date: Wed, 16 Mar 2022 20:57:18 +0200
Subject: [PATCH 2/2] add tests for nix eval and nix-instantiate

---
 tests/eval.nix |  5 +++++
 tests/eval.sh  | 29 +++++++++++++++++++++++++++++
 tests/local.mk |  1 +
 3 files changed, 35 insertions(+)
 create mode 100644 tests/eval.nix
 create mode 100644 tests/eval.sh

diff --git a/tests/eval.nix b/tests/eval.nix
new file mode 100644
index 000000000..befbd17a9
--- /dev/null
+++ b/tests/eval.nix
@@ -0,0 +1,5 @@
+{
+  int = 123;
+  str = "foo";
+  attr.foo = "bar";
+}
diff --git a/tests/eval.sh b/tests/eval.sh
new file mode 100644
index 000000000..2e5ceb969
--- /dev/null
+++ b/tests/eval.sh
@@ -0,0 +1,29 @@
+source common.sh
+
+clearStore
+
+testStdinHeredoc=$(nix eval -f - <<EOF
+{
+  bar = 3 + 1;
+  foo = 2 + 2;
+}
+EOF
+)
+[[ $testStdinHeredoc == '{ bar = 4; foo = 4; }' ]]
+
+nix eval --expr 'assert 1 + 2 == 3; true'
+
+[[ $(nix eval int -f "./eval.nix") == 123 ]]
+[[ $(nix eval str -f "./eval.nix") == '"foo"' ]]
+[[ $(nix eval str --raw -f "./eval.nix") == 'foo' ]]
+[[ $(nix eval attr -f "./eval.nix") == '{ foo = "bar"; }' ]]
+[[ $(nix eval attr --json -f "./eval.nix") == '{"foo":"bar"}' ]]
+[[ $(nix eval int -f - < "./eval.nix") == 123 ]]
+
+
+nix-instantiate --eval -E 'assert 1 + 2 == 3; true'
+[[ $(nix-instantiate -A int --eval "./eval.nix") == 123 ]]
+[[ $(nix-instantiate -A str --eval "./eval.nix") == '"foo"' ]]
+[[ $(nix-instantiate -A attr --eval "./eval.nix") == '{ foo = "bar"; }' ]]
+[[ $(nix-instantiate -A attr --eval --json "./eval.nix") == '{"foo":"bar"}' ]]
+[[ $(nix-instantiate -A int --eval - < "./eval.nix") == 123 ]]
diff --git a/tests/local.mk b/tests/local.mk
index 8032fc38a..f84c20fc7 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -52,6 +52,7 @@ nix_tests = \
   build-remote-content-addressed-floating.sh \
   nar-access.sh \
   pure-eval.sh \
+  eval.sh \
   ca/post-hook.sh \
   repl.sh \
   ca/repl.sh \