E004: Invalid Attribute Set Merge

Severity: Error

cannot merge `int` with `{ name: string }`: both sides must be attribute sets

The // (update) operator requires both operands to be attribute sets. This error appears when one or both sides have a non-attrset type.

Common causes

• Using // on a value that isn’t an attribute set:

  42 // { x = 1; }   # int is not an attrset
  

• A variable intended to hold an attrset actually holds a different type due to a logic error upstream.
• Merging the return value of a function that doesn’t return an attrset.

How to fix

• Verify that both sides of // are attribute sets.
• If one side is conditional, make sure all branches return an attrset:

  (if cond then { a = 1; } else {}) // { b = 2; }
  

• Check whether you meant + (concatenation/addition) instead of // (merge).