EvalState::realiseContext(): Allow access to the entire closure

Fixes #11030.

(cherry picked from commit 08361f031d)

# Conflicts:
#	src/libexpr/eval.cc
#	tests/functional/import-from-derivation.nix
#	tests/functional/import-from-derivation.sh

tests/functional/import-from-derivation.nix

@@ -0,0 +1,52 @@
+with import <config>;
+
+rec {
+  bar = mkDerivation {
+    name = "bar";
+    builder = builtins.toFile "builder.sh"
+      ''
+        echo 'builtins.add 123 456' > $out
+      '';
+  };
+
+  value =
+    # Test that pathExists can check the existence of /nix/store paths
+    assert builtins.pathExists bar;
+    import bar;
+
+  result = mkDerivation {
+    name = "foo";
+    builder = builtins.toFile "builder.sh"
+      ''
+        echo -n FOO${toString value} > $out
+      '';
+  };
+
+  addPath = mkDerivation {
+    name = "add-path";
+    src = builtins.filterSource (path: type: true) result;
+    builder = builtins.toFile "builder.sh"
+      ''
+        echo -n BLA$(cat $src) > $out
+      '';
+  };
+
+  step1 = mkDerivation {
+    name = "step1";
+    buildCommand = ''
+      mkdir -p $out
+      echo 'foo' > $out/bla
+    '';
+  };
+
+  addPathExpr = mkDerivation {
+    name = "add-path";
+    inherit step1;
+    buildCommand = ''
+      mkdir -p $out
+      echo "builtins.path { path = \"$step1\"; sha256 = \"7ptL+pnrZXnSa5hwwB+2SXTLkcSb5264WGGokN8OXto=\"; }" > $out/default.nix
+    '';
+  };
+
+  importAddPathExpr = import addPathExpr;
+}

tests/functional/import-from-derivation.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+TODO_NixOS
+
+clearStoreIfPossible
+
+export NIX_PATH=config="${config_nix}"
+
+if nix-instantiate --readonly-mode ./import-from-derivation.nix -A result; then
+    echo "read-only evaluation of an imported derivation unexpectedly failed"
+    exit 1
+fi
+
+outPath=$(nix-build ./import-from-derivation.nix -A result --no-out-link)
+
+[ "$(cat "$outPath")" = FOO579 ]
+
+# Check that we can have access to the entire closure of a derivation output.
+nix build --no-link --restrict-eval -I src=. -f ./import-from-derivation.nix importAddPathExpr -v
+
+# FIXME: the next tests are broken on CA.
+if [[ -n "${NIX_TESTS_CA_BY_DEFAULT:-}" ]]; then
+    exit 0
+fi
+
+# Test filterSource on the result of a derivation.
+outPath2=$(nix-build ./import-from-derivation.nix -A addPath --no-out-link)
+[[ "$(cat "$outPath2")" = BLAFOO579 ]]
+
+# Test that IFD works with a chroot store.
+if canUseSandbox; then
+
+    store2="$TEST_ROOT/store2"
+    store2_url="$store2?store=$NIX_STORE_DIR"
+
+    # Copy the derivation outputs to the chroot store to avoid having
+    # to actually build anything, as that would fail due to the lack
+    # of a shell in the sandbox. We only care about testing the IFD
+    # semantics.
+    for i in bar result addPath; do
+        nix copy --to "$store2_url" --no-check-sigs "$(nix-build ./import-from-derivation.nix -A "$i" --no-out-link)"
+    done
+
+    clearStore
+
+    outPath_check=$(nix-build ./import-from-derivation.nix -A result --no-out-link --store "$store2_url")
+    [[ "$outPath" = "$outPath_check" ]]
+    [[ ! -e "$outPath" ]]
+    [[ -e "$store2/nix/store/$(basename "$outPath")" ]]
+
+    outPath2_check=$(nix-build ./import-from-derivation.nix -A addPath --no-out-link --store "$store2_url")
+    [[ "$outPath2" = "$outPath2_check" ]]
+fi