add an impl of Expr::show for ExprInheritFrom that doesn't crash

ExprVar::show() assumes it has a name. dynamic inherits do not
necessarily (ever?) have a name.

Change-Id: If10893188e307431da17f0c1bd0787adc74f7141

2 files changed, 35 insertions, 0 deletions

diff --git a/tests/unit/libexpr/expr-print.cc b/tests/unit/libexpr/expr-print.cc
new file mode 100644
index 000000000..aa25d00df
--- /dev/null
+++ b/tests/unit/libexpr/expr-print.cc
@@ -0,0 +1,34 @@
+#include <sstream>
+#include <string_view>
+
+#include <gtest/gtest.h>
+
+#include "tests/libexpr.hh"
+
+#include "nixexpr.hh"
+#include "ref.hh"
+
+namespace nix
+{
+
+using namespace testing;
+struct ExprPrintingTests : LibExprTest
+{
+    void test(Expr const & expr, std::string_view expected)
+    {
+        std::stringstream out;
+        expr.show(state.symbols, out);
+        ASSERT_EQ(out.str(), expected);
+    }
+};
+
+TEST_F(ExprPrintingTests, ExprInheritFrom)
+{
+    // ExprInheritFrom has its own show() impl.
+    // If it uses its parent class's impl it will crash.
+    auto inheritSource = make_ref<ExprVar>(state.symbols.create("stdenv"));
+    ExprInheritFrom const eInheritFrom(noPos, 0, inheritSource);
+    test(eInheritFrom, "(/* expanded inherit (expr) */ stdenv)");
+}
+
+}
diff --git a/tests/unit/meson.build b/tests/unit/meson.build
index 17d089f18..a6719a060 100644
--- a/tests/unit/meson.build
+++ b/tests/unit/meson.build
@@ -186,6 +186,7 @@ libexpr_tests_sources = files(
   'libexpr/primops.cc',
   'libexpr/search-path.cc',
   'libexpr/trivial.cc',
+  'libexpr/expr-print.cc',
   'libexpr/value/context.cc',
   'libexpr/value/print.cc',
 )