bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Ryo Furue]

Hi emacs maintainers,

1. Open an empty Ruby source code, say "tmp.rb".
2. Type the following:

#!/usr/bin/ruby
base = ?a.ord - 1

On hitting the return key at the end of the second line, the cursor
moves below "a", not to the top of the third line. The indentation
state seems to be confused.  I did this test with "emacs -q" .

?a is a valid Ruby syntax for string literal.  After writing this, I learned
that "a".ord is equivalent (I think), so I already have a workaround.

Hope this helps,

Ryo



In GNU Emacs 25.1.50.1 (x86_64-apple-darwin15.6.0, NS appkit-1404.47
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 of 2016-07-27 built on furufuru-mac.yes.jamstec.go.jp
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bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Dmitry Gutov]

Hi!

On 08/08/2016 06:50 AM, Ryo Furue wrote:

> 1. Open an empty Ruby source code, say "tmp.rb".
> 2. Type the following:
>
> #!/usr/bin/ruby
> base = ?a.ord - 1
>
> On hitting the return key at the end of the second line, the cursor
> moves below "a", not to the top of the third line. The indentation
> state seems to be confused.  I did this test with "emacs -q" .

Thanks for the report. I'd like to fix it sometime, but it's not a big 
priority, considering this syntax is usually discouraged:

https://github.com/bbatsov/ruby-style-guide#no-character-literals

> ?a is a valid Ruby syntax for string literal.  After writing this, I learned
> that "a".ord is equivalent (I think)

Yes, in Ruby 1.9 and newer, it's a full equivalent.

bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Ryo Furue]

Hi,

> Thanks for the report. I'd like to fix it sometime, but it's not a big
> priority, considering this syntax is usually discouraged:
>
> https://github.com/bbatsov/ruby-style-guide#no-character-literals

Thank you for the link! It seems very comprehensive and must be useful
for many other issues, too.

I agree the bug I reported isn't a big issue.

>> ?a is a valid Ruby syntax for string literal.  After writing this, I
>> learned
>> that "a".ord is equivalent (I think)
>
> Yes, in Ruby 1.9 and newer, it's a full equivalent.

After my last message, I learned that Ruby has abandoned the idea of
"character type" and instead of elevating ?a to a proper character
literal, it has made it equivalent to a single-character string "a".
So, a String is no longer a sequence of individual characters (because
"character" has no representation in the language).  "a".ord returns
the character code of this single-character string but "abc".ord
ignores the "bc" part.  I don't think that's a clean design, but
perhaps it's the simplest, practical one, in the face of various
character encodings. . . .  That makes me wonder how Haskell handles
unicode.  In that language, "String" is an alias for "[Char]"  (list
of Char's). . . . I digressed.

Cheers,

Ryo

bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Dmitry Gutov]

Sorry for digging this up, just looking through old issues.

On 11.08.2016 09:41, Ryo Furue wrote:

>>> ?a is a valid Ruby syntax for string literal.  After writing this, I
>>> learned
>>> that "a".ord is equivalent (I think)
>>
>> Yes, in Ruby 1.9 and newer, it's a full equivalent.
> 
> After my last message, I learned that Ruby has abandoned the idea of
> "character type" and instead of elevating ?a to a proper character
> literal, it has made it equivalent to a single-character string "a".
> So, a String is no longer a sequence of individual characters (because
> "character" has no representation in the language).  "a".ord returns
> the character code of this single-character string but "abc".ord
> ignores the "bc" part.  I don't think that's a clean design, but
> perhaps it's the simplest, practical one, in the face of various
> character encodings. . . .

This syntax there is purely for compatibility, I believe.

>  That makes me wonder how Haskell handles
> unicode.  In that language, "String" is an alias for "[Char]"  (list
> of Char's). . . . I digressed.

Types in a statically typed language are a bit of a different beast. 
E.g., you can eliminate a lot of associated overhead during compilation. 
Not so with a dynamically typed langues.

For posterity, a fix for the reported problem should look like the patch 
at the end of this message. I'm not going to commit it, though (or, at 
least, not in its current form) because Ruby makes it non-trivial to 
distinguish between these literals and the ternary operator:

 > abc ?( 1+ 2) : 4
=> 3

 > def dee(arg);
 > dee ?( 1+ 2) : 4
SyntaxError ((irb):27: syntax error, unexpected tINTEGER, expecting end)
dee ?( 1+ 2) : 4

Hopefully, the syntax will just be removed in some near future version 
of Ruby and save us the trouble. But here's the patch. To go in, it 
would have to be accompanied by some extra code looking around to 
determine the context.

diff --git a/lisp/progmodes/ruby-mode.el b/lisp/progmodes/ruby-mode.el
index 3effb6ed66..bd74e71f6a 100644
--- a/lisp/progmodes/ruby-mode.el
+++ b/lisp/progmodes/ruby-mode.el
@@ -1854,9 +1854,9 @@ ruby-syntax-propertize
       (syntax-propertize-rules
        ;; $' $" $` .... are variables.
        ;; ?' ?" ?` are character literals (one-char strings in 1.9+).
-      ("\\([?$]\\)[#\"'`:?]"
+      ("\\([?$]\\)[#\"'`:?[:alnum:]]"
         (1 (if (save-excursion
-                (nth 3 (syntax-ppss (match-beginning 0))))
+                (nth 8 (syntax-ppss (match-beginning 0))))
                ;; Within a string, skip.
                (ignore
                 (goto-char (match-end 1)))

bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Lars Ingebrigtsen]

Dmitry Gutov <dgutov@yandex.ru> writes:

> Hopefully, the syntax will just be removed in some near future version
> of Ruby and save us the trouble. But here's the patch. To go in, it
> would have to be accompanied by some extra code looking around to
> determine the context.

So it sounds like the conclusion here is that we're not going to change
the behaviour here, and I'm closing this bug.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#24181: 25.1.50; ruby mode: wrong auto indent after "?" string literal

[Dmitry Gutov]

On 15.08.2021 15:26, Lars Ingebrigtsen wrote:
> Dmitry Gutov<dgutov@yandex.ru>  writes:
> 
>> Hopefully, the syntax will just be removed in some near future version
>> of Ruby and save us the trouble. But here's the patch. To go in, it
>> would have to be accompanied by some extra code looking around to
>> determine the context.
> So it sounds like the conclusion here is that we're not going to change
> the behaviour here, and I'm closing this bug.

For now, at least. Since there's not much apparent user demand for it.

Whether that's just because there are not too many Emacs users doing 
Ruby these days, or because the syntax really fell out of favor, I don't 
know.

Hope it's the latter.