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] 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("."));