libexpr/builtins: Document appendContext

Change-Id: Ic45e0d4f6f1646552a7162bd8916f63fc11e5e62

lix/libexpr/builtins/appendContext.md

@@ -0,0 +1,6 @@
+---
+name: appendContext
+args: [s, ctx]
+---
+
+Appends the attribute set `ctx` as a context to the string `s`, see [`getContext`](#builtins-getContext) for details on the format of the context.

lix/libexpr/extra-primops.hh

@@ -14,6 +14,7 @@ void prim_fetchGit(EvalState & state, Value * * args, Value & v);
 void prim_fetchTarball(EvalState & state, Value * * args, Value & v);
 void prim_fetchurl(EvalState & state, Value * * args, Value & v);
 void prim_fromTOML(EvalState & state, Value * * args, Value & v);
+void prim_appendContext(EvalState & state, Value ** args, Value & v);
 void prim_getContext(EvalState & state, Value * * args, Value & v);
 void prim_hasContext(EvalState & state, Value * * args, Value & v);
 void prim_unsafeDiscardOutputDependency(EvalState & state, Value * * args, Value & v);

lix/libexpr/meson.build

@@ -56,6 +56,7 @@ builtin_definitions = files(
   'builtins/addErrorContext.md',
   'builtins/all.md',
   'builtins/any.md',
+  'builtins/appendContext.md',
   'builtins/attrNames.md',
   'builtins/attrValues.md',
   'builtins/baseNameOf.md',

lix/libexpr/primops/context.cc

@@ -165,7 +165,7 @@ void prim_getContext(EvalState & state, Value * * args, Value & v)
    See the commentary above unsafeGetContext for details of the
    context representation.
 */
-static void prim_appendContext(EvalState & state, Value * * args, Value & v)
+void prim_appendContext(EvalState & state, Value ** args, Value & v)
 {
     NixStringContext context;
     auto orig = state.forceString(*args[0], context, noPos, "while evaluating the first argument passed to builtins.appendContext");
@@ -241,11 +241,4 @@ static void prim_appendContext(EvalState & state, Value * * args, Value & v)
 
     v.mkString(orig, context);
 }
-
-static RegisterPrimOp primop_appendContext({
-    .name = "__appendContext",
-    .arity = 2,
-    .fun = prim_appendContext
-});
-
 }