OrganizeImports: regex alternation (|) in groups config doesn't match imports correctly

[He-Pin]

Problem

When using regex patterns with the alternation operator | in the OrganizeImports groups configuration, the regex fails to match imports that individual patterns (without alternation) match correctly.

Example

Given this .scalafix.conf:

OrganizeImports {
  groups = [
    "re:^(org\\.apache\\.pekko\\.?|pekko\\.)",
    "org.slf4j.",
    "*"
  ]
  removeUnused = true
}

The regex ^(org\.apache\.pekko\.?|pekko\.) should match both:

• import org.apache.pekko (syntax string: org.apache.pekko)
• import pekko.actor.Actor (syntax string: pekko.actor.Actor)

Expected: Both imports go to group 0.

Actual: Neither import goes to group 0. Both fall through to the * catch-all group.

What works

Each pattern works correctly when used standalone (without alternation):

# This matches `import org.apache.pekko` correctly:
groups = ["re:org\\.apache\\.pekko", "*"]

# This matches `import pekko.*` correctly:
groups = ["pekko.", "*"]

What doesn't work

Combining them with | fails:

# Neither pattern matches when combined:
groups = ["re:org\\.apache\\.pekko|pekko\\.", "*"]

# Also fails with ^ anchor:
groups = ["re:^(org\\.apache\\.pekko|pekko\\.)", "*"]

# Also fails with \\.? optional dot:
groups = ["re:^(org\\.apache\\.pekko\\.?|pekko\\.)", "*"]

Root cause analysis

Looking at ImportMatcher.scala, the RE matcher uses:

pattern findPrefixMatchOf i.syntax map (_.end) getOrElse 0

The findPrefixMatchOf method should handle alternation correctly since it uses Java's java.util.regex engine. I verified with a standalone Java test that Pattern.compile("^(org\\.apache\\.pekko\\.?|pekko\\.)").matcher("org.apache.pekko").lookingAt() returns true with end() = 16.

The bug may be in how the HOCON config parser handles the | character in quoted strings, or in how the Regex is constructed from the parsed pattern string. Specifically, the parse function:

case p if p.startsWith("re:") => RE(new Regex(p stripPrefix "re:"))

may produce an incorrectly escaped regex string when | is present in the HOCON value.

Environment

• scalafix version: 0.14.7
• sbt-scalafix version: 0.14.7
• Scala versions tested: 2.13.18, 3.3.x

Workaround

Use two separate group entries instead of regex alternation:

groups = [
  "re:org\\.apache\\.pekko",
  "pekko.",
  "*"
]

This places the imports in adjacent groups (with a blank line between them when using blankLines = Auto), which is not ideal but functional.

[bjaglin]

Thanks for the detailed report!