const_source_location

        # Module.const_source_location

(from ruby core)
---
    mod.const_source_location(sym, inherit=true)   -> [String, Integer]
    mod.const_source_location(str, inherit=true)   -> [String, Integer]

---

Returns the Ruby source filename and line number containing the
definition of the constant specified. If the named constant is not
found, `nil` is returned. If the constant is found, but its source
location can not be extracted (constant is defined in C code), empty
array is returned.

*inherit* specifies whether to lookup in `mod.ancestors` (`true` by
default).

    # test.rb:
    class A         # line 1
      C1 = 1
      C2 = 2
    end

    module M        # line 6
      C3 = 3
    end

    class B < A     # line 10
      include M
      C4 = 4
    end

    class A # continuation of A definition
      C2 = 8 # constant redefinition; warned yet allowed
    end

    p B.const_source_location('C4')           # => ["test.rb", 12]
    p B.const_source_location('C3')           # => ["test.rb", 7]
    p B.const_source_location('C1')           # => ["test.rb", 2]

    p B.const_source_location('C3', false)    # => nil  -- don't lookup in ancestors

    p A.const_source_location('C2')           # => ["test.rb", 16] -- actual (last) definition place

    p Object.const_source_location('B')       # => ["test.rb", 10] -- top-level constant could be looked through Object
    p Object.const_source_location('A')       # => ["test.rb", 1] -- class reopening is NOT considered new definition

    p B.const_source_location('A')            # => ["test.rb", 1]  -- because Object is in ancestors
    p M.const_source_location('A')            # => ["test.rb", 1]  -- Object is not ancestor, but additionally checked for modules

    p Object.const_source_location('A::C1')   # => ["test.rb", 2]  -- nesting is supported
    p Object.const_source_location('String')  # => []  -- constant is defined in C code