Move support for comments to fromJSONC

src/libexpr/include/nix/expr/json-to-value.hh

@@ -12,6 +12,13 @@ struct Value;
 
 MakeError(JSONParseError, Error);
 
-void parseJSON(EvalState & state, const std::string_view & s, Value & v);
+/**
+ * Parse the string into the Value
+ * @param state
+ * @param s
+ * @param v
+ * @param allowComments Whether to allow comments in the JSON
+ */
+void parseJSON(EvalState & state, const std::string_view & s, Value & v, bool allowComments = false);
 
 } // namespace nix

src/libexpr/json-to-value.cc

@@ -201,11 +201,11 @@ public:
     }
 };
 
-void parseJSON(EvalState & state, const std::string_view & s_, Value & v)
+void parseJSON(EvalState & state, const std::string_view & s_, Value & v, bool allowComments)
 {
     JSONSax parser(state, v);
     bool res = json::sax_parse(
-        s_, &parser, nlohmann::detail::input_format_t::json, /* strict= */ true, /* ignore_comments= */ true);
+        s_, &parser, nlohmann::detail::input_format_t::json, /* strict= */ true, /* ignore_comments= */ allowComments);
     if (!res)
         throw JSONParseError("Invalid JSON Value");
 }

src/libexpr/primops.cc

@@ -2470,11 +2470,11 @@ static RegisterPrimOp primop_toJSON({
 });
 
 /* Parse a JSON string to a value. */
-static void prim_fromJSON(EvalState & state, const PosIdx pos, Value ** args, Value & v)
+static void prim_fromJSON(EvalState & state, const PosIdx pos, Value ** args, Value & v, bool allow_comments)
 {
     auto s = state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.fromJSON");
     try {
-        parseJSON(state, s, v);
+        parseJSON(state, s, v, allow_comments);
     } catch (JSONParseError & e) {
         e.addTrace(state.positions[pos], "while decoding a JSON string");
         throw;
@@ -2492,10 +2492,39 @@ static RegisterPrimOp primop_fromJSON({
       ```
 
       returns the value `{ x = [ 1 2 3 ]; y = null; }`.
+    )",
+    .fun =
+        [](EvalState & state, const PosIdx pos, Value ** args, Value & v) {
+            return prim_fromJSON(state, pos, args, v, false);
+        },
+});
+
+static RegisterPrimOp primop_fromJSONC({
+    .name = "__fromJSONC",
+    .args = {"e"},
+    .doc = R"(
+      Convert a JSON string, potentially with comments, to a Nix value.
+      For example,
+
+      ```nix
+      builtins.fromJSONC ''
+      {
+       // This is a comment
+       "x": [1, 2, 3],
+       /* This is another comment */
+       "y": null
+      }
+      ''
+      ```
+
+      returns the value `{ x = [ 1 2 3 ]; y = null; }`.
 
       This function supports JSON with comments.
     )",
-    .fun = prim_fromJSON,
+    .fun =
+        [](EvalState & state, const PosIdx pos, Value ** args, Value & v) {
+            return prim_fromJSON(state, pos, args, v, true);
+        },
 });
 
 /* Store a string in the Nix store as a source file that can be used