Purpose
- Minimal Go query in VS Code; variables, constraints, and results for a concrete bug pattern.

Target Pattern
- Methods defined on value receivers that write to a field have no effect (receiver is copied).
- Safer alternative: method should use a pointer receiver.

Query
  import go
  from Method m, Variable recv, Write w, Field f
  where recv = m.getReceiver() and
        w.writesField(recv.getARead(), f, _) and
        not recv.getType() instanceof PointerType
  select w, "This update to " + f + " has no effect, because " + recv + " is not a pointer."

Structure (analogy to SQL)
- import: include standard Go library (import go).
- from: declare typed variables to range over (Method, Variable, Write, Field).
- where: constrain relationships among variables with predicates.
- select: emit results; message can concatenate strings and AST entities.

Key Predicates/Classes
- Method.getReceiver(): receiver variable of a method.
- Write.writesField(baseRead, field, idx): a write whose LHS writes field of a base expression.
- Variable.getARead(): a read expression of the variable (used to match Write receiver base).
- PointerType: type test to exclude pointer receivers.

Usage Hints
- Use hasQualifiedName(pkg, name) to narrow functions/methods by package.
- Start with quick query in the VS Code CodeQL extension; paste query under "import go".
- Click results to jump to the write site; refine constraints if needed.

Extensions
- Add a guard to exclude writes to fields of temporary copies (e.g., values returned from functions).
- Restrict to exported methods/types, or to specific packages.
- Convert to a path query to show flows leading to the write (optional).