From f4454aac9f002c33b84bb52e0bba2a46ea6170cd Mon Sep 17 00:00:00 2001
From: Cole Helbling <cole.e.helbling@outlook.com>
Date: Mon, 18 Dec 2023 15:22:09 -0800
Subject: [PATCH] nix shell: reflect command line order in PATH order

Prior to this change, Nix would prepend every installable to the PATH
list in order to ensure that installables appeared before the current
PATH from the ambient environment.

With this change, all the installables are still prepended to the PATH,
but in the same order as they appear on the command line. This means
that the first of two packages that expose an executable `hello` would
appear in the PATH first, and thus be executed first.

See the test in the prior commit for a more concrete example.
---
 src/libcmd/installables.cc | 14 ++++++++++++++
 src/libcmd/installables.hh |  7 +++++++
 src/nix/run.cc             |  9 ++++++---
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index be9ebe9ca..736c41a1e 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -729,6 +729,20 @@ StorePathSet Installable::toStorePathSet(
     return outPaths;
 }
 
+StorePaths Installable::toStorePaths(
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode, OperateOn operateOn,
+    const Installables & installables)
+{
+    StorePaths outPaths;
+    for (auto & path : toBuiltPaths(evalStore, store, mode, operateOn, installables)) {
+        auto thisOutPaths = path.outPaths();
+        outPaths.insert(outPaths.end(), thisOutPaths.begin(), thisOutPaths.end());
+    }
+    return outPaths;
+}
+
 StorePath Installable::toStorePath(
     ref<Store> evalStore,
     ref<Store> store,
diff --git a/src/libcmd/installables.hh b/src/libcmd/installables.hh
index c8ad41388..95e8841ca 100644
--- a/src/libcmd/installables.hh
+++ b/src/libcmd/installables.hh
@@ -172,6 +172,13 @@ struct Installable
         OperateOn operateOn,
         const Installables & installables);
 
+    static std::vector<StorePath> toStorePaths(
+        ref<Store> evalStore,
+        ref<Store> store,
+        Realise mode,
+        OperateOn operateOn,
+        const Installables & installables);
+
     static StorePath toStorePath(
         ref<Store> evalStore,
         ref<Store> store,
diff --git a/src/nix/run.cc b/src/nix/run.cc
index efc0c56a1..9bca5b9d0 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -114,7 +114,7 @@ struct CmdShell : InstallablesCommand, MixEnvironment
 
         setEnviron();
 
-        auto unixPath = tokenizeString<Strings>(getEnv("PATH").value_or(""), ":");
+        std::vector<std::string> pathAdditions;
 
         while (!todo.empty()) {
             auto path = todo.front();
@@ -122,7 +122,7 @@ struct CmdShell : InstallablesCommand, MixEnvironment
             if (!done.insert(path).second) continue;
 
             if (true)
-                unixPath.push_front(store->printStorePath(path) + "/bin");
+                pathAdditions.push_back(store->printStorePath(path) + "/bin");
 
             auto propPath = CanonPath(store->printStorePath(path)) + "nix-support" + "propagated-user-env-packages";
             if (auto st = accessor->maybeLstat(propPath); st && st->type == SourceAccessor::tRegular) {
@@ -131,7 +131,10 @@ struct CmdShell : InstallablesCommand, MixEnvironment
             }
         }
 
-        setenv("PATH", concatStringsSep(":", unixPath).c_str(), 1);
+        auto unixPath = tokenizeString<Strings>(getEnv("PATH").value_or(""), ":");
+        unixPath.insert(unixPath.begin(), pathAdditions.begin(), pathAdditions.end());
+        auto unixPathString = concatStringsSep(":", unixPath);
+        setenv("PATH", unixPathString.c_str(), 1);
 
         Strings args;
         for (auto & arg : command) args.push_back(arg);