libcmd: munge evalSettings in the right place

these must be tampered with before the evaluator is created, *never*
after. doing it any other way leads to interesting things like #596.

fixes #596

Change-Id: Iea253ccce44b94b1243833837a3df93c795967d9

lix/libcmd/command.hh

@@ -77,7 +77,7 @@ struct EvalCommand : virtual StoreCommand, MixEvalArgs
 
     ref<Store> getEvalStore();
 
-    ref<eval_cache::CachingEvaluator> getEvaluator();
+    virtual ref<eval_cache::CachingEvaluator> getEvaluator();
 
 private:
     std::shared_ptr<Store> evalStore;
@@ -114,6 +114,8 @@ struct SourceExprCommand : virtual Args, MixFlakeOptions
 
     SourceExprCommand();
 
+    ref<eval_cache::CachingEvaluator> getEvaluator() override;
+
     Installables parseInstallables(
         EvalState & state, ref<Store> store, std::vector<std::string> ss);
 

lix/libcmd/installables.cc

@@ -212,9 +212,7 @@ void SourceExprCommand::completeInstallable(EvalState & state, AddCompletions &
         if (file) {
             completions.setType(AddCompletions::Type::Attrs);
 
-            evalSettings.pureEval.override(false);
             auto evaluator = getEvaluator();
-            evaluator->paths.allowedPaths.reset();
 
             Expr & e = evaluator->parseExprFromFile(
                 resolveExprPath(evaluator->paths.checkSourcePath(lookupFileArg(*evaluator, *file)))
@@ -427,6 +425,16 @@ ref<eval_cache::EvalCache> openEvalCache(
     }
 }
 
+ref<eval_cache::CachingEvaluator> SourceExprCommand::getEvaluator()
+{
+    // FIXME: backward compatibility hack
+    if (file) {
+        evalSettings.pureEval.override(false);
+    }
+
+    return EvalCommand::getEvaluator();
+}
+
 Installables SourceExprCommand::parseInstallables(
     EvalState & state, ref<Store> store, std::vector<std::string> ss)
 {
@@ -436,12 +444,6 @@ Installables SourceExprCommand::parseInstallables(
         if (file && expr)
             throw UsageError("'--file' and '--expr' are exclusive");
 
-        // FIXME: backward compatibility hack
-        if (file) {
-            evalSettings.pureEval.override(false);
-            getEvaluator()->paths.allowedPaths.reset();
-        }
-
         auto evaluator = getEvaluator();
         auto vFile = evaluator->mem.allocValue();
 

tests/functional/impure-eval.sh

@@ -33,3 +33,6 @@ simpleTest 'builtins.currentSystem' 'bar' --eval-system 'bar'
 ## `eval-system` overrides `system`
 simpleTest 'builtins.currentSystem' 'bar' --system 'foo' --eval-system 'bar'
 simpleTest 'builtins.currentSystem' 'baz' --system 'foo' --eval-system 'baz'
+
+## `-f` honors nix-path
+[ "$(nix eval --option nix-path "foo=$PWD" -f '<foo/eval.nix>' attr.foo)" = '"bar"' ]