Misc #20407: Question about applying encoding modifier to an interpolated Regexp

• Status: Open
• Assignee: -

[andrykonchin (Andrew Konchin)]

I am wondering how Regexp encoding modifiers (u, s, e, n) interfere in encoding negotiation of parts/fragments in an interpolated Regexp literal.

Examples #1

# encoding: us-ascii

# Unicode: Ф - U+0424
# windows-1251: Ф - 0xD4

# without encoding modifier
puts /a #{ "\xd4".force_encoding("windows-1251") } c/.encoding    # Windows-1251
puts /a #{ "b".encode("windows-1251") } c/.encoding               # US-ASCII
puts /a #{ "\u0424".force_encoding("UTF-8") } c/.encoding         # UTF-8
puts /a #{ "\xc2\xa1".b } c/.encoding                             # ASCII-8BIT

# with encoding modifier
puts /a #{ "\xd4".force_encoding("windows-1251") } c/e.encoding   # Windows-1251
puts /a #{ "b".encode("windows-1251") } c/e.encoding              # EUC-JP
puts /a #{ "\u0424".force_encoding("UTF-8") } c/e.encoding        # UTF-8
puts /a #{ "\xc2\xa1".b } c/e.encoding                            # ASCII-8BIT

# string interpolation
puts "a #{ "\xd4".force_encoding("windows-1251") } c".encoding    # Windows-1251
puts "a #{ "b".encode("windows-1251") } c".encoding               # Windows-1251
puts "a #{ "\u0424".force_encoding("UTF-8") } c".encoding         # UTF-8
puts "a #{ "\xc2\xa1".b } c".encoding                             # ASCII-8BIT

Example #2

# encoding: utf-8

# windows-1251: Ф - 0xD4
# unicode: Ф - U+0424

# without encoding modifier
puts /a #{ "\xd4".force_encoding("windows-1251") } c/.encoding    # Windows-1251
puts /a #{ "b".encode("windows-1251") } c/.encoding               # US-ASCII
puts /a #{ "\u0424".force_encoding("UTF-8") } c/.encoding         # UTF-8
puts /a #{ "\xc2\xa1".b } c/.encoding                             # ASCII-8BIT

# with encoding modifier
puts /a #{ "\xd4".force_encoding("windows-1251") } c/e.encoding   # Windows-1251
puts /a #{ "b".encode("windows-1251") } c/e.encoding              # EUC-JP
puts /a #{ "\u0424".force_encoding("UTF-8") } c/e.encoding        # UTF-8
puts /a #{ "\xc2\xa1".b } c/e.encoding                            # ASCII-8BIT

# string interpolation
puts "a #{ "\xd4".force_encoding("windows-1251") } c".encoding    # Windows-1251
puts "a #{ "b".encode("windows-1251") } c".encoding               # UTF-8
puts "a #{ "\u0424".force_encoding("UTF-8") } c".encoding         # UTF-8
puts "a #{ "\xc2\xa1".b } c".encoding                             # ASCII-8BIT

In the examples above the e modifier changes Regexp's encoding only in one case when Regexp's encoding would be US-ASCII without the modifier:

# encoding: us-ascii

puts /a #{ "b".encode("windows-1251") } c/.encoding                        # US-ASCII
puts /a #{ "b".encode("windows-1251") } c/e.encoding                       # EUC-JP

# encoding: utf-8

puts /a #{ "b".encode("windows-1251") } c/.encoding                        # US-ASCII
puts /a #{ "b".encode("windows-1251") } c/e.encoding                       # EUC-JP

And the e modifier doesn't change Regexp's final encoding in all the other cases either Regexp's encoding without modifier is a file source encoding or ASCII-8BIT.

Looking at the following example:

# encoding: us-ascii

# without modifier
p /\xc2\xa1 #{ "a" }\xc2\xa1/.encoding                                 # ASCII-8BIT
p /a #{ "\xc2\xa1".force_encoding("EUC-JP") } b/.encoding              # EUC-JP
p /a #{ "\xc2\xa1".b } b/.encoding                                     # ASCII-8BIT

# with modifier
p /\xc2\xa1 #{ "a" }\xc2\xa1/e.encoding                                # EUC-JP
p /a #{ "\xc2\xa1".force_encoding("EUC-JP") } b/e.encoding             # EUC-JP
p /a #{ "\xc2\xa1".b } b/e.encoding                                    # ASCII-8BIT

we can notice that the e modifier changes ASCII-8BIT to EUC-JP in the first case (/\xc2\xa1 #{ "a" }\xc2\xa1/) but doesn't in the third one (/a #{ "\xc2\xa1".b } b/). So I assume that the e modifier could be applied to the Regexp fragments (\xc2\xa1 and \xc2\xa1) before encoding negotiation and not to the whole result after negotiation.

Could you please clarify how it works?

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

• Related to Misc #20406: Question about Regexp encoding negotiation added

[Eregon (Benoit Daloze)]

• Related to Bug #20466: Interpolated regular expressions have different encoding than interpolated strings added

[naruse (Yui NARUSE)]

I checked the related source code especially about rb_reg_preprocess_dregexp. It wrongly calls rb_reg_preprocess with overwriting fixed_enc instead of inheriting it.

It seems to raise error if the resulted encoding of the regexp is other than EUC-JP in this case.
(US-ASCII case also should raise error or show a warning comparing //n's behavior)

I'm still wondering whether we should fix this issue because there is a trade off between compatibility and the merit of this improvement)