Issue #11868 has been updated by Tsuyoshi Sawada.


If the character position can be achieved in addition to the line number, then the "hint" can be reconstructed. (However, I think the syntax error information being bound to the raised error rather than being output to `$stderr` would be much cleaner solution.)

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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-56830

* Author: Joe Rafaniello
* Status: Open
* Priority: Normal
* Assignee: 
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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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