Add builtins.unsafeGetLambdaPos

This is useful for a potential pure-Nix implementation of NixOS#3904.
lf- · Aug 8, 2020 · 189795f · 189795f
1 parent edfd676
commit 189795f
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Showing 3 changed files with 17 additions and 0 deletions.
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
@@ -444,6 +444,17 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         v.listElems()[n++] = i;
 }
 
+/* Return position information of the given lambda. */
+void prim_unsafeGetLambdaPos(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    /* ensure the argument is a function */
+    state.forceValue(*args[0], pos);
+    if (args[0]->type != tLambda) {
+        throwTypeError(pos, "value is %1% while a lambda was expected", *args[0]);
+    }
+
+    state.mkPos(v, &args[0]->lambda.fun->pos);
+}
 
 static void prim_abort(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
@@ -2314,6 +2325,7 @@ void EvalState::createBaseEnv()
     addPrimOp("__isBool", 1, prim_isBool);
     addPrimOp("__isPath", 1, prim_isPath);
     addPrimOp("__genericClosure", 1, prim_genericClosure);
+    addPrimOp("__unsafeGetLambdaPos", 1, prim_unsafeGetLambdaPos);
     addPrimOp("abort", 1, prim_abort);
     addPrimOp("__addErrorContext", 2, prim_addErrorContext);
     addPrimOp("__tryEval", 1, prim_tryEval);

diff --git a/tests/lang/eval-okay-getlambdapos.exp b/tests/lang/eval-okay-getlambdapos.exp
@@ -0,0 +1 @@
+{ column = 9; file = "eval-okay-getlambdapos.nix"; line = 2; }
diff --git a/tests/lang/eval-okay-getlambdapos.nix b/tests/lang/eval-okay-getlambdapos.nix
@@ -0,0 +1,4 @@
+let
+  fun = { foo }: {};
+  pos = builtins.unsafeGetLambdaPos fun;
+in { inherit (pos) column line; file = baseNameOf pos.file; }