method_source can raise a EOFError.

[ghost]

To reproduce:

require 'rubygems'
require 'method_source'

block     = proc { puts "Hello, world!" }
original = block.source

File.open('/tmp/foo.txt', 'a') { |f| f.write(original) }

buf     = File.read '/tmp/foo.txt'
block = eval(buf, binding, __FILE__, __LINE__)

block.source

If you change the mode from a to w, it works fine.
It looks like method_source loops past the end of the file (valid_expression? never returns true).

[ghost]

You'll need to run this twice or three times to trigger it.

[rf-]

Try changing the last line of your file to puts block.source. I'm not sure why it advances a line each time you run it, but the root issue in your example is that you're lying to eval about the location of the code.

[ghost]

Adjusting __LINE__ and __FILE__ in Kernel#eval, I still get the same error:

require 'rubygems'
require 'method_source'

block     = proc { puts "Hello, world!" }
original = block.source

File.open('/tmp/foo.txt', 'a') { |f| f.write(original) }
line = File.readlines('/tmp/foo.txt').size

buf     = File.read '/tmp/foo.txt'
block   = eval(buf, binding, '/tmp/foo.txt', line )

block.source

[banister]

It should be able to show the prompt source in this example, but it fails with an EOFError

90:   NAV_PROMPT = [
 91:                 proc do |_, level, pry|
 92:                   tree = pry.binding_stack.map { |b| Pry.view_clip(b.eval("self")) }.join " / "
 93:                   "[#{pry.input_array.size}] (pry) #{tree}: #{level}> "
 94:                 end,
 95:                 proc do |_, level, pry|
 96:                   tree = pry.binding_stack.map { |b| Pry.view_clip(b.eval("self")) }.join " / "
 97:                   "[#{pry.input_array.size}] (pry) #{tree}: #{level}* "
 98:                 end,
 99:                ]
100: 
101:   # Deal with the ^D key being pressed, different behaviour in
102:   # different cases:
103:   # 1) In an expression     - behave like `!` command   (clear input buffer)
104:   # 2) At top-level session - behave like `exit command (break out of repl loop)
105:   # 3) In a nested session  - behave like `cd ..`       (pop a binding)
106:   DEFAULT_CONTROL_D_HANDLER = proc do |eval_string, _pry_|
107:     if !eval_string.empty?
108:       # clear input buffer
109:       eval_string.replace("")
110:     elsif _pry_.binding_stack.one?
111:       # ^D at top-level breaks out of loop
112:       _pry_.binding_stack.clear
113:       throw(:breakout)
114:     else
115:       # otherwise just pops a binding
116:       _pry_.binding_stack.pop
117:     end
118:   end
[37] (pry) unknown: 0> Pry.config.prompt.first.source_location
=> ["/Users/john/.rvm/gems/ruby-1.9.2-p290/gems/pry-0.9.8pre4/lib/pry.rb", 91]
[38] (pry) unknown: 0> Pry.config.prompt.first.source
EOFError: end of file reached
from /Users/john/.rvm/gems/ruby-1.9.2-p290/gems/method_source-0.7.0/lib/method_source.rb:44:in `readline'
[39] (pry) unknown: 0>