Issue #11868 has been updated by Joe Rafaniello.


Nobuyoshi Nakada wrote:
> [`assert_valid_syntax`](https://github.com/ruby/ruby/blob/trunk/test/lib/test/unit/assertions.rb#L450) may help you.

Thank you for reviewing this so quickly and the suggestion.   I forgot that test/unit had such an assertion.  

Although, I think this assertion doesn't provide the information I need.

RubyVM::InstructionSequence.compile provides this information to standard error:  the line number(s), specific error(s), and the location "hint(s)".  The line number is very important for style checkers such as rubocop as it helps identify the location of the invalid syntax.  The hint is also very helpful.

For example:

~~~~
$ cat test.rb

class Joe
  def test-
  end
end
~~~~

Running rubocop: 

~~~~
$ rubocop test.rb

Inspecting 1 file
E

Offenses:

test.rb:2:11: E: unexpected token tMINUS
  def test-
          ^

1 file inspected, 1 offense detected
~~~~

With a 4 line file, this is not that difficult but with much larger files and many changes happening, it's easy to make a mistake or typo and not "see" the problem immediately.

It would be great to have access to this useful information directly in ruby through `lineno` and `hint` methods (or better names) and not have to capture and parse STDERR manually.

Thank you for the consideration.



----------------------------------------
Feature #11868: Proposal for RubyVM::InstructionSequence.compile to return an object containing the syntax error information currently written to STDERR
https://bugs.ruby-lang.org/issues/11868#change-55755

* Author: Joe Rafaniello
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
Currently, RubyVM::InstructionSequence.compile or RubyVM::InstructionSequence.new return a new InstructionSequence for valid ruby.

For invalid syntax, a SyntaxError is raised with a message of 'compile error'.  Meanwhile, the useful information, line number(s) and hint(s) to the invalid syntax location, is printed on standard error.  I am proposing this information be returned as an object in the event of a SyntaxError.

For example, here's good syntax:

~~~
RubyVM::InstructionSequence.new("x =1")
# => <RubyVM::InstructionSequence:<compiled>@<compiled>>
~~~


Here's bad syntax:

~~~
RubyVM::InstructionSequence.new("puts 'hi'\n puts 'hi2'\n\nthis.is -> not -> valid $ruby:syntax")

# => SyntaxError: compile error

# The useful hint and line number(s) are on standard error:
<compiled>:4: syntax error, unexpected keyword_not, expecting keyword_do_LAMBDA or tLAMBEG
this.is -> not -> valid $ruby:syntax
              ^
<compiled>:4: syntax error, unexpected tGVAR, expecting keyword_do_LAMBDA or tLAMBEG
this.is -> not -> valid $ruby:syntax
                             ^
~~~

Some ideas:

1. Add methods to all SyntaxError exceptions to get all parse failures.  For example: `syntax_error.parse_failures.each {|f| puts f.lineno; puts f.hint }`.  In the above example, it failed on line 4 twice and we see two "hints."

2. Create a new method to RubyVM::InstructionSequence to check ruby syntax that would allow us to see if the syntax is valid and if not,  the lineno and 'hint' for each parse failure.

Use case:  Rubocop[a] and other utilities[b] are really complicated and check for valid ruby syntax by creating a process to run ruby -wc with the script.
[a] https://github.com/bbatsov/rubocop/blob/86e1acf67794bf6dd5d65812b91df475e44fa320/spec/support/mri_syntax_checker.rb#L51-L63
[b] https://github.com/ManageIQ/manageiq/blob/6725fe52222c07d576a18126d2ff825ddc6dffd0/gems/pending/util/miq-syntax-checker.rb#L8-L13

It would be nice to remove all of this complexity and use RubyVM::InstructionSequence, which already has the information we need but in a more user friendly format.

Thanks!
Joe Rafaniello



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