puppetlabs/puppet · error · ArgumentError

Cannot transform object of class %{klass}

Error message

Cannot transform object of class %{klass}

What it means

Raised by CollectorTransformer#query_Object, the fallback handler for a collector search expression whose node class has no dedicated query_ translator. Collector queries (<| ... |>) support only a small grammar — comparisons (==/!=/and/or/not), tag checks, parenthesized expressions, and qualified names; anything else (function calls, arithmetic, literal structures) reaches query_Object and is rejected with the offending class name.

Source

Thrown at lib/puppet/pops/evaluator/collector_transformer.rb:171

  def query_LiteralNumber(o, scope)
    @@evaluator.evaluate(o, scope)
  end

  def query_LiteralUndef(o, scope)
    nil
  end

  def query_QualifiedName(o, scope)
    @@evaluator.evaluate(o, scope)
  end

  def query_ParenthesizedExpression(o, scope)
    query(o.expr, scope)
  end

  def query_Object(o, scope)
    raise ArgumentError, _("Cannot transform object of class %{klass}") % { klass: o.class }
  end

  def match_AccessExpression(o, scope)
    pops_object = @@evaluator.evaluate(o, scope)

    # Convert to Puppet 3 style objects since that is how they are represented
    # in the catalog.
    @@evaluator.convert(pops_object, scope, nil)
  end

  def match_AndExpression(o, scope)
    left_match = match(o.left_expr, scope)
    right_match = match(o.right_expr, scope)
    [left_match, 'and', right_match]
  end

  def match_OrExpression(o, scope)
    left_match = match(o.left_expr, scope)

View on GitHub (pinned to e227c27540)

Solutions

1. Precompute values into variables and compare against them: `$wanted = regsubst('a','b','c')` then `<| title == $wanted |>`.
2. Restructure the query to use only supported operators: ==, !=, and, or, not, and `tag` comparisons.
3. For logic too complex for collectors, collect broadly and filter in a loop over the collected resources instead.

Example fix

# before
File<| title == regsubst('base','prod','stage') |>   # Cannot transform object of class Puppet::Pops::Model::CallExpression

# after
$wanted = regsubst('base','prod','stage')
File<| title == $wanted |>

# Precompute every dynamic operand, then keep the query grammar pure:
$wanted = regsubst('base','prod','stage')
File<| title == $wanted |>

When it happens

Trigger: `<| title == regsubst('a','b','c') |>`, `<| (foo + 1) == 3 |>`, `<| defined(File) |>` — any CallExpression, ArithmeticExpression, or other unsupported node occupying a query-grammar position inside `<| ... |>` or `Type<| ... |>`.

Common situations: Trying to make collection searches 'dynamic' by calling functions or computing values inline; porting complex SQL-like filters into collectors; assuming general Puppet expressions are valid inside collector brackets.

Related errors

• Cannot transform a number to a tag
• Function Load Error for function '%{function_name}': %{messa
• A required parameter cannot be added after an optional param
• block_param accepts max 2 arguments (type, name), got %{size
• Attempt to redefine block

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/ec85f72dbb113256. Report an issue: GitHub.