init

scope.cc

@@ -0,0 +1,52 @@
+#include <nix/expr/primops.hh>
+#include <nix/expr/eval.hh>
+#include <nix/expr/eval-inline.hh>
+#include <nix/expr/nixexpr.hh>
+#include <nix/expr/attr-set.hh>
+
+using namespace nix;
+
+static void prim_scope(EvalState & state, const PosIdx pos, Value ** args, Value & v)
+{
+    std::vector<Symbol> path;
+
+    state.forceStringNoCtx(*args[0], pos, "'scope' path argument");
+    auto s = std::string(args[0]->string_view());
+    if (s.empty())
+        state.error<TypeError>("'scope' requires a non-empty path")
+            .atPos(pos)
+            .debugThrow();
+    size_t start = 0;
+    while (start < s.size()) {
+        auto dot = s.find('.', start);
+        if (dot == std::string::npos) {
+            path.push_back(state.symbols.create(s.substr(start)));
+            break;
+        }
+        path.push_back(state.symbols.create(s.substr(start, dot - start)));
+        start = dot + 1;
+    }
+
+    // Build nested attrset from inside out
+    // Given path [a, b, c] and value v: { a = { b = { c = v; }; }; }
+    Value * inner = args[1];
+    for (auto it = path.rbegin(); it != path.rend(); ++it) {
+        auto attrs = state.buildBindings(1);
+        attrs.insert(*it, inner);
+        Value * wrapper = state.allocValue();
+        wrapper->mkAttrs(attrs.finish());
+        inner = wrapper;
+    }
+    v = *inner;
+}
+
+static RegisterPrimOp rp({
+    .name = "scope",
+    .args = {"path", "value"},
+    .doc = R"(
+      Construct a nested attribute set from a dotted string path and a value.
+
+      Example: `scope "a.b.c" 42` evaluates to `{ a = { b = { c = 42; }; }; }`.
+    )",
+    .fun = prim_scope,
+});