Module: McpAuthorization::Diagnostics

Defined in:
lib/mcp_authorization/diagnostics.rb

Overview

Shared diagnostic helpers used by both the field-level RbsSchemaCompiler#predicate_excluded? and the tool-level Tool#gates_pass? paths.

Lives in its own module so the two predicate sites — field-level (compile time) and tool-level (request time) — share a single “Did you mean?” warning implementation. Avoids two copies of Levenshtein drifting.

Class Method Summary collapse

Class Method Details

.levenshtein(a, b) ⇒ Integer

Minimal Levenshtein distance for typo suggestions.

Iterative two-row implementation — O(m*n) time, O(m) extra space. Used only in development for “Did you mean?” suggestions, so the naive version is fine.

: (String, String) -> Integer

Parameters:

  • a (String)
  • b (String)

Returns:

  • (Integer) 


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# File 'lib/mcp_authorization/diagnostics.rb', line 68

def levenshtein(a, b)
  m, n = a.length, b.length
  d = Array.new(m + 1) { |i| i }
  (1..n).each do |j|
    prev = d[0]
    d[0] = j
    (1..m).each do |i|
      cost = a[i - 1] == b[j - 1] ? 0 : 1
      temp = d[i]
      d[i] = [d[i] + 1, d[i - 1] + 1, prev + cost].min
      prev = temp
    end
  end
  d[m]
end

.warn_unknown_predicate(name, server_context, site:) ⇒ void

This method returns an undefined value.

Emit a development-mode warning when a predicate method is not found on the server context. Helps catch typos like @feture(:x) or gate :feture, :sms.

: (String | Symbol, untyped, Symbol) -> void

Parameters:

  • name (String, Symbol) —

    The predicate name attempted (e.g. “feature” or :gate).

  • server_context (Object) —

    The context the predicate was looked up on.

  • site (Symbol) —

    :field or :tool — controls the suggestion phrasing.



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# File 'lib/mcp_authorization/diagnostics.rb', line 22

def warn_unknown_predicate(name, server_context, site:)
  return unless defined?(Rails) && Rails.respond_to?(:env) && Rails.env.local?

  str = name.to_s
  available = server_context.class.public_instance_methods(true)
    .select { |m| m.to_s.end_with?("?") }
    .map { |m| m.to_s.chomp("?") }
  best = available.min_by { |a| levenshtein(a, str) }
  suggestion = best && levenshtein(best, str) <= 3 ? best : nil

  hint =
    case site
    when :tool  then suggestion ? " Did you mean gate :#{suggestion}?" : ""
    when :field then suggestion ? " Did you mean @#{suggestion}?" : ""
    else             suggestion ? " Did you mean #{suggestion}?" : ""
    end

  surface =
    case site
    when :tool  then "Gate predicate"
    when :field then "Predicate"
    else             "Predicate"
    end

  fallthrough =
    case site
    when :tool  then "Tool will be shown to all users."
    when :field then "Field will be shown to all users."
    else             ""
    end

  Rails.logger&.warn(
    "[McpAuthorization] #{surface} '#{str}?' not found on #{server_context.class}.#{hint} #{fallthrough}".strip
  )
end