From ac5081d28035ef8d6a907fc3bff812d534719f74 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 13 Nov 2020 17:49:27 +0100
Subject: [PATCH 1/2] nix-build: Fix #4197 output order regression

---
 src/nix-build/nix-build.cc | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index f60e0706c..74fafd426 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -487,6 +487,7 @@ static void main_nix_build(int argc, char * * argv)
     else {
 
         std::vector<StorePathWithOutputs> pathsToBuild;
+        std::vector<std::pair<StorePath, std::string>> pathsToBuildOrdered;
 
         std::map<StorePath, std::pair<size_t, StringSet>> drvMap;
 
@@ -498,6 +499,7 @@ static void main_nix_build(int argc, char * * argv)
                 throw Error("derivation '%s' lacks an 'outputName' attribute", store->printStorePath(drvPath));
 
             pathsToBuild.push_back({drvPath, {outputName}});
+            pathsToBuildOrdered.push_back({drvPath, {outputName}});
 
             auto i = drvMap.find(drvPath);
             if (i != drvMap.end())
@@ -513,25 +515,23 @@ static void main_nix_build(int argc, char * * argv)
 
         std::vector<StorePath> outPaths;
 
-        for (auto & [drvPath, info] : drvMap) {
-            auto & [counter, wantedOutputs] = info;
+        for (auto & [drvPath, outputName] : pathsToBuildOrdered) {
+            auto & [counter, _wantedOutputs] = drvMap.at({drvPath});
             std::string drvPrefix = outLink;
             if (counter)
                 drvPrefix += fmt("-%d", counter + 1);
 
             auto builtOutputs = store->queryDerivationOutputMap(drvPath);
 
-            for (auto & outputName : wantedOutputs) {
-                auto outputPath = builtOutputs.at(outputName);
+            auto outputPath = builtOutputs.at(outputName);
 
-                if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>()) {
-                    std::string symlink = drvPrefix;
-                    if (outputName != "out") symlink += "-" + outputName;
-                    store2->addPermRoot(outputPath, absPath(symlink));
-                }
-
-                outPaths.push_back(outputPath);
+            if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>()) {
+                std::string symlink = drvPrefix;
+                if (outputName != "out") symlink += "-" + outputName;
+                store2->addPermRoot(outputPath, absPath(symlink));
             }
+
+            outPaths.push_back(outputPath);
         }
 
         logger->stop();

From d264da8d968bb3afe29def1f4aff0f91f25e36c6 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 13 Nov 2020 17:49:55 +0100
Subject: [PATCH 2/2] tests: Test #4197 nix-build output order regression

---
 tests/nix-build-examples.nix | 33 +++++++++++++++++++++++++++++++++
 tests/nix-build.sh           | 15 +++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 tests/nix-build-examples.nix

diff --git a/tests/nix-build-examples.nix b/tests/nix-build-examples.nix
new file mode 100644
index 000000000..e54dbbf62
--- /dev/null
+++ b/tests/nix-build-examples.nix
@@ -0,0 +1,33 @@
+with import ./config.nix;
+
+rec {
+
+  input0 = mkDerivation {
+    name = "dependencies-input-0";
+    buildCommand = "mkdir $out; echo foo > $out/bar";
+  };
+
+  input1 = mkDerivation {
+    name = "dependencies-input-1";
+    buildCommand = "mkdir $out; echo FOO > $out/foo";
+  };
+
+  input2 = mkDerivation {
+    name = "dependencies-input-2";
+    buildCommand = ''
+      mkdir $out
+      echo BAR > $out/bar
+      echo ${input0} > $out/input0
+    '';
+  };
+
+  body = mkDerivation {
+    name = "dependencies-top";
+    builder = ./dependencies.builder0.sh + "/FOOBAR/../.";
+    input1 = input1 + "/.";
+    input2 = "${input2}/.";
+    input1_drv = input1;
+    meta.description = "Random test package";
+  };
+
+}
diff --git a/tests/nix-build.sh b/tests/nix-build.sh
index 3123c6da3..44a5a14cd 100644
--- a/tests/nix-build.sh
+++ b/tests/nix-build.sh
@@ -26,3 +26,18 @@ outPath2=$(nix-build $(nix-instantiate dependencies.nix)!out --no-out-link)
 
 outPath2=$(nix-store -r $(nix-instantiate --add-root $TEST_ROOT/indirect dependencies.nix)!out)
 [[ $outPath = $outPath2 ]]
+
+# The order of the paths on stdout must correspond to the -A options
+# https://github.com/NixOS/nix/issues/4197
+
+input0="$(nix-build nix-build-examples.nix -A input0 --no-out-link)"
+input1="$(nix-build nix-build-examples.nix -A input1 --no-out-link)"
+input2="$(nix-build nix-build-examples.nix -A input2 --no-out-link)"
+body="$(nix-build nix-build-examples.nix -A body --no-out-link)"
+
+outPathsA="$(echo $(nix-build nix-build-examples.nix -A input0 -A input1 -A input2 -A body --no-out-link))"
+[[ "$outPathsA" = "$input0 $input1 $input2 $body" ]]
+
+# test a different ordering to make sure it fails, not just in 23 out of 24 permutations
+outPathsB="$(echo $(nix-build nix-build-examples.nix -A body -A input1 -A input2 -A input0 --no-out-link))"
+[[ "$outPathsB" = "$body $input1 $input2 $input0" ]]