method_source not working with Prism due to different SyntaxError messages

[eregon]

Running https://github.com/banister/method_source 's test suite passes on ruby master but fails with RUBYOPT=--parser=prism bundle exec rake:

Failures:

  1) MethodSource::CodeHelpers should not raise an error on broken lines: def\na\n(); end
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):3: syntax errors found (SyntaxError)
         1 | BEGIN{throw :valid}
       > 2 | def
           |    ^ expected an `end` to close the `def` statement
           |    ^ expected a delimiter to close the parameters
       > 3 | 
           | ^ unexpected end of file, assuming it is closing the parent top level context
     
           | ^ unexpected end of file; expected a method name
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  2) MethodSource::CodeHelpers should not raise an error on broken lines: p = <<FOO\nlots\nand\nlots of\nfoo\nFOO
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):3: syntax error found (SyntaxError)
         1 | BEGIN{throw :valid}
         2 | p = <<FOO
       > 3 | 
           | ^ could not find a terminator for the heredoc
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  3) MethodSource::CodeHelpers should not raise an error on broken lines: [\n:lets,\n'list',\n[/nested/\n], things ]
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):2: syntax error found (SyntaxError)
         1 | BEGIN{throw :valid}
       > 2 | [
           |  ^ expected a `]` to close the array
         3 | 
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  4) MethodSource::CodeHelpers should not raise an error on broken lines: abc =~ /hello\n/
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):2: syntax error found (SyntaxError)
         1 | BEGIN{throw :valid}
       > 2 | abc =~ /hello
           |        ^ expected a closing delimiter for the regular expression
         3 | 
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  5) MethodSource::CodeHelpers should not raise an error on broken lines: issue = %W/\n343/
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):2: syntax error found (SyntaxError)
         1 | BEGIN{throw :valid}
       > 2 | issue = %W/
           |         ^~~ expected a closing delimiter for the `%W` list
         3 | 
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  6) MethodSource::CodeHelpers should not raise an error on broken lines: puts 1, 2,\n3
     Failure/Error: eval("BEGIN{throw :valid}\n#{str}")
     
     SyntaxError:
       (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):2: syntax error found (SyntaxError)
         1 | BEGIN{throw :valid}
       > 2 | puts 1, 2,
           |          ^ expected an argument
         3 | 
     # ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'
     # ./lib/method_source/code_helpers.rb:71:in 'block in MethodSource::CodeHelpers#complete_expression?'
     # ./lib/method_source/code_helpers.rb:70:in 'Kernel#catch'
     # ./lib/method_source/code_helpers.rb:70:in 'MethodSource::CodeHelpers#complete_expression?'
     # ./spec/method_source/code_helpers_spec.rb:22:in 'block (4 levels) in <top (required)>'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'Integer#upto'
     # ./spec/method_source/code_helpers_spec.rb:21:in 'block (3 levels) in <top (required)>'

  7) MethodSource Methods should return source for an *_evaled method
     Failure/Error: raise SourceNotFoundError, "Could not parse source for #{name}: #{e.message}"
     
     MethodSource::SourceNotFoundError:
       Could not parse source for hello_name: (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):3: syntax errors found
         1 | BEGIN{throw :valid}
         2 |   def hello_#{name}(*args)
       > 3 | 
           | ^ expected an `end` to close the `def` statement
     
           | ^ unexpected end of file, assuming it is closing the parent top level context
     # ./lib/method_source.rb:29:in 'MethodSource.source_helper'
     # ./lib/method_source.rb:115:in 'MethodSource::MethodExtensions#source'
     # ./spec/method_source_spec.rb:75:in 'block (3 levels) in <top (required)>'
     # ------------------
     # --- Caused by: ---
     # SyntaxError:
     #   (eval at /home/eregon/code/method_source/lib/method_source/code_helpers.rb:71):3: syntax errors found (SyntaxError)
     #     1 | BEGIN{throw :valid}
     #     2 |   def hello_#{name}(*args)
     #   > 3 | 
     #       | ^ expected an `end` to close the `def` statement
     #   
     #       | ^ unexpected end of file, assuming it is closing the parent top level context
     #   ./lib/method_source/code_helpers.rb:71:in 'Kernel#eval'

Finished in 0.00674 seconds (files took 0.04986 seconds to load)
36 examples, 7 failures

Failed examples:

rspec './spec/method_source/code_helpers_spec.rb[1:2]' # MethodSource::CodeHelpers should not raise an error on broken lines: def\na\n(); end
rspec './spec/method_source/code_helpers_spec.rb[1:3]' # MethodSource::CodeHelpers should not raise an error on broken lines: p = <<FOO\nlots\nand\nlots of\nfoo\nFOO
rspec './spec/method_source/code_helpers_spec.rb[1:4]' # MethodSource::CodeHelpers should not raise an error on broken lines: [\n:lets,\n'list',\n[/nested/\n], things ]
rspec './spec/method_source/code_helpers_spec.rb[1:5]' # MethodSource::CodeHelpers should not raise an error on broken lines: abc =~ /hello\n/
rspec './spec/method_source/code_helpers_spec.rb[1:6]' # MethodSource::CodeHelpers should not raise an error on broken lines: issue = %W/\n343/
rspec './spec/method_source/code_helpers_spec.rb[1:9]' # MethodSource::CodeHelpers should not raise an error on broken lines: puts 1, 2,\n3
rspec ./spec/method_source_spec.rb:74 # MethodSource Methods should return source for an *_evaled method

Because of https://github.com/banister/method_source/blob/06f21c66380c64ff05c8031c0208eef240da0e83/lib/method_source/code_helpers.rb#L125-L131

Is there a better way with Prism to find "subsets of SyntaxErrors that can be fixed by adding more input to the buffer" than matching messages (which seems very brittle)?

[eregon]

@kddnewton Any thoughts regarding that last sentence? IIRC IRB also wanted this predicate for syntax errors.

[kddnewton]

To answer your question — there is not currently a way. I think that discussion is still taking place here: https://bugs.ruby-lang.org/issues/20024.