getDefaultNixPath: actually respect {restrict,pure}-eval

Previously, getDefaultNixPath was called too early: at initialisation time, before CLI and config have been processed, when `restrictEval` and `pureEval` both have their default value `false`. Call it when initialising the EvalState instead, and use `setDefault`.
NixOS · Jan 25, 2023 · b60f41d · b60f41d
1 parent f233fd4
commit b60f41d
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Showing 4 changed files with 37 additions and 18 deletions.
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
@@ -519,6 +519,7 @@ EvalState::EvalState(
     static_assert(sizeof(Env) <= 16, "environment must be <= 16 bytes");
 
     /* Initialise the Nix expression search path. */
+    evalSettings.nixPath.setDefault(evalSettings.getDefaultNixPath());
     if (!evalSettings.pureEval) {
         for (auto & i : _searchPath) addToSearchPath(i);
         for (auto & i : evalSettings.nixPath.get()) addToSearchPath(i);
@@ -2472,30 +2473,40 @@ std::ostream & operator << (std::ostream & str, const ExternalValueBase & v) {
 
 EvalSettings::EvalSettings()
 {
-    auto var = getEnv("NIX_PATH");
-    if (var) nixPath = parseNixPath(*var);
 }
 
+/* impure => NIX_PATH or a default path
+ * restrict-eval => NIX_PATH
+ * pure-eval => empty
+ */
 Strings EvalSettings::getDefaultNixPath()
 {
-    Strings res;
-    auto add = [&](const Path & p, const std::string & s = std::string()) {
-        if (pathExists(p)) {
-            if (s.empty()) {
-                res.push_back(p);
-            } else {
-                res.push_back(s + "=" + p);
+    if (pureEval)
+        return {};
+
+    auto var = getEnv("NIX_PATH");
+    if (var) {
+        return parseNixPath(*var);
+    } else {
+        Strings res;
+        auto add = [&](const Path & p, const std::string & s = std::string()) {
+            if (pathExists(p)) {
+                if (s.empty()) {
+                    res.push_back(p);
+                } else {
+                    res.push_back(s + "=" + p);
+                }
             }
+        };
+
+        if (!restrictEval && !pureEval) {
+            add(getHome() + "/.nix-defexpr/channels");
+            add(settings.nixStateDir + "/profiles/per-user/root/channels/nixpkgs", "nixpkgs");
+            add(settings.nixStateDir + "/profiles/per-user/root/channels");
         }
-    };
 
-    if (!evalSettings.restrictEval && !evalSettings.pureEval) {
-        add(getHome() + "/.nix-defexpr/channels");
-        add(settings.nixStateDir + "/profiles/per-user/root/channels/nixpkgs", "nixpkgs");
-        add(settings.nixStateDir + "/profiles/per-user/root/channels");
+        return res;
     }
-
-    return res;
 }
 
 bool EvalSettings::isPseudoUrl(std::string_view s)

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
@@ -570,7 +570,7 @@ struct EvalSettings : Config
 {
     EvalSettings();
 
-    static Strings getDefaultNixPath();
+    Strings getDefaultNixPath();
 
     static bool isPseudoUrl(std::string_view s);
 
@@ -580,7 +580,7 @@ struct EvalSettings : Config
         "Whether builtin functions that allow executing native code should be enabled."};
 
     Setting<Strings> nixPath{
-        this, getDefaultNixPath(), "nix-path",
+        this, {}, "nix-path",
         "List of directories to be searched for `<...>` file references."};
 
     Setting<bool> restrictEval{

diff --git a/tests/nix_path.sh b/tests/nix_path.sh
@@ -12,3 +12,8 @@ nix-instantiate --eval -E '<by-relative-path/simple.nix>' --restrict-eval
 
 [[ $(nix-instantiate --find-file by-absolute-path/simple.nix) = $PWD/simple.nix ]]
 [[ $(nix-instantiate --find-file by-relative-path/simple.nix) = $PWD/simple.nix ]]
+
+unset NIX_PATH
+
+[[ $(nix-instantiate --option nix-path by-relative-path=. --find-file by-relative-path/simple.nix) = "$PWD/simple.nix" ]]
+[[ $(NIX_PATH= nix-instantiate --option nix-path by-relative-path=. --find-file by-relative-path/simple.nix) = "$PWD/simple.nix" ]]
diff --git a/tests/restricted.sh b/tests/restricted.sh
@@ -17,6 +17,9 @@ nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../src/nix-channel'
 (! nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>')
 nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>' -I src=.
 
+# no default NIX_PATH
+(unset NIX_PATH; ! nix-instantiate --restrict-eval --find-file .)
+
 p=$(nix eval --raw --expr "builtins.fetchurl file://$(pwd)/restricted.sh" --impure --restrict-eval --allowed-uris "file://$(pwd)")
 cmp $p restricted.sh