* Check for duplicate attributes and formal parameters in Nix

expressions.

tests/lang/parse-fail-dup-attrs-1.nix

@@ -0,0 +1,4 @@
+{ x = 123;
+  y = 456;
+  x = 789;
+}

tests/lang/parse-fail-dup-attrs-2.nix

@@ -0,0 +1,13 @@
+let {
+
+  as = {
+    x = 123;
+    y = 456;
+  };
+
+  bs = {
+    x = 789;
+    inherit (as) x;
+  };
+  
+}

tests/lang/parse-fail-dup-attrs-3.nix

@@ -0,0 +1,13 @@
+let {
+
+  as = {
+    x = 123;
+    y = 456;
+  };
+
+  bs = rec {
+    x = 789;
+    inherit (as) x;
+  };
+  
+}

tests/lang/parse-fail-dup-formals.nix

@@ -0,0 +1 @@
+{x, y, x}: x