From 42f22f37df2947f4231743e172747b5afab2b708 Mon Sep 17 00:00:00 2001
From: Qyriad <qyriad@qyriad.me>
Date: Mon, 24 Jun 2024 14:33:12 -0600
Subject: [PATCH] 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
---
 src/libexpr/nixexpr.cc           |  7 +++++++
 src/libexpr/nixexpr.hh           |  3 ++-
 tests/unit/libexpr/expr-print.cc | 34 ++++++++++++++++++++++++++++++++
 tests/unit/meson.build           |  1 +
 4 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 tests/unit/libexpr/expr-print.cc

diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index bc53ca053..bdf117641 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -50,6 +50,13 @@ void ExprVar::show(const SymbolTable & symbols, std::ostream & str) const
     str << symbols[name];
 }
 
+void ExprInheritFrom::show(SymbolTable const & symbols, std::ostream & str) const
+{
+    str << "inherit (";
+    fromExpr->show(symbols, str);
+    str << ")";
+}
+
 void ExprSelect::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(";
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 703a32e8f..25ba94595 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -154,7 +154,8 @@ struct ExprInheritFrom : ExprVar
         this->fromWith = nullptr;
     }
 
-    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env);
+    void show(SymbolTable const & symbols, std::ostream & str) const override;
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
 };
 
 struct ExprSelect : Expr
diff --git a/tests/unit/libexpr/expr-print.cc b/tests/unit/libexpr/expr-print.cc
new file mode 100644
index 000000000..25840efff
--- /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, "inherit (stdenv)");
+}
+
+}
diff --git a/tests/unit/meson.build b/tests/unit/meson.build
index 2b5471526..e2ca95629 100644
--- a/tests/unit/meson.build
+++ b/tests/unit/meson.build
@@ -185,6 +185,7 @@ 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',
 )