From 0b56c98b1c10c3ea16b8cda9644e5b656b9d7b67 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 13 Jun 2024 18:18:36 +0200
Subject: [PATCH] C API: Value -> nix_value

---
 src/libexpr-c/nix_api_expr.h          |  3 ++-
 src/libexpr-c/nix_api_expr_internal.h |  5 +++++
 src/libexpr-c/nix_api_value.cc        | 11 ++++++++---
 src/libexpr-c/nix_api_value.h         |  5 ++++-
 tests/unit/libexpr/nix_api_value.cc   | 10 ++++++++++
 5 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/src/libexpr-c/nix_api_expr.h b/src/libexpr-c/nix_api_expr.h
index cb6c00385..140da9e52 100644
--- a/src/libexpr-c/nix_api_expr.h
+++ b/src/libexpr-c/nix_api_expr.h
@@ -36,7 +36,8 @@ typedef struct EvalState EvalState; // nix::EvalState
  * @struct Value
  * @see value_manip
  */
-typedef void Value; // nix::Value
+typedef struct nix_value nix_value;
+[[deprecated("use nix_value instead")]] typedef nix_value Value;
 
 // Function prototypes
 /**
diff --git a/src/libexpr-c/nix_api_expr_internal.h b/src/libexpr-c/nix_api_expr_internal.h
index 7743849fd..5a875ef39 100644
--- a/src/libexpr-c/nix_api_expr_internal.h
+++ b/src/libexpr-c/nix_api_expr_internal.h
@@ -20,6 +20,11 @@ struct ListBuilder
     nix::ListBuilder builder;
 };
 
+struct nix_value
+{
+    nix::Value value;
+};
+
 struct nix_string_return
 {
     std::string str;
diff --git a/src/libexpr-c/nix_api_value.cc b/src/libexpr-c/nix_api_value.cc
index 978cf7f43..dd8382133 100644
--- a/src/libexpr-c/nix_api_value.cc
+++ b/src/libexpr-c/nix_api_value.cc
@@ -64,6 +64,11 @@ static nix::Value & check_value_out(Value * value)
     return v;
 }
 
+static inline nix_value * as_nix_value_ptr(nix::Value * v)
+{
+    return reinterpret_cast<nix_value *>(v);
+}
+
 /**
  * Helper function to convert calls from nix into C API.
  *
@@ -159,7 +164,7 @@ Value * nix_alloc_value(nix_c_context * context, EvalState * state)
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        Value * res = state->state.allocValue();
+        nix_value * res = as_nix_value_ptr(state->state.allocValue());
         nix_gc_incref(nullptr, res);
         return res;
     }
@@ -345,7 +350,7 @@ Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalSt
         if (attr) {
             nix_gc_incref(nullptr, attr->value);
             state->state.forceValue(*attr->value, nix::noPos);
-            return attr->value;
+            return as_nix_value_ptr(attr->value);
         }
         nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
         return nullptr;
@@ -380,7 +385,7 @@ nix_get_attr_byidx(nix_c_context * context, const Value * value, EvalState * sta
         *name = ((const std::string &) (state->state.symbols[a.name])).c_str();
         nix_gc_incref(nullptr, a.value);
         state->state.forceValue(*a.value, nix::noPos);
-        return a.value;
+        return as_nix_value_ptr(a.value);
     }
     NIXC_CATCH_ERRS_NULL
 }
diff --git a/src/libexpr-c/nix_api_value.h b/src/libexpr-c/nix_api_value.h
index 244860707..acc4a1969 100644
--- a/src/libexpr-c/nix_api_value.h
+++ b/src/libexpr-c/nix_api_value.h
@@ -35,8 +35,11 @@ typedef enum {
 } ValueType;
 
 // forward declarations
-typedef void Value;
+typedef struct nix_value nix_value;
 typedef struct EvalState EvalState;
+
+[[deprecated("use nix_value instead")]] typedef nix_value Value;
+
 // type defs
 /** @brief Stores an under-construction set of bindings
  * @ingroup value_manip
diff --git a/tests/unit/libexpr/nix_api_value.cc b/tests/unit/libexpr/nix_api_value.cc
index c71593c85..b674d8681 100644
--- a/tests/unit/libexpr/nix_api_value.cc
+++ b/tests/unit/libexpr/nix_api_value.cc
@@ -4,16 +4,26 @@
 #include "nix_api_util_internal.h"
 #include "nix_api_expr.h"
 #include "nix_api_value.h"
+#include "nix_api_expr_internal.h"
 
 #include "tests/nix_api_expr.hh"
 #include "tests/string_callback.hh"
 
 #include "gmock/gmock.h"
+#include <cstddef>
 #include <cstdlib>
 #include <gtest/gtest.h>
 
 namespace nixC {
 
+TEST_F(nix_api_expr_test, as_nix_value_ptr)
+{
+    // nix_alloc_value casts nix::Value to nix_value
+    // It should be obvious from the decl that that works, but if it doesn't,
+    // the whole implementation would be utterly broken.
+    ASSERT_EQ(sizeof(nix::Value), sizeof(nix_value));
+}
+
 TEST_F(nix_api_expr_test, nix_value_get_int_invalid)
 {
     ASSERT_EQ(0, nix_get_int(ctx, nullptr));