func emitAssertion()

in Sources/_StringProcessing/Compiler.swift [188:258]
47 lines of code
16 McCabe index (conditional complexity)

  func emitAssertion(_ kind: AST.Atom.AssertionKind) throws {
    // FIXME: Depends on API model we have... We may want to
    // think through some of these with API interactions in mind
    //
    // This might break how we use `bounds` for both slicing
    // and things like `firstIndex`, that is `firstIndex` may
    // need to supply both a slice bounds and a per-search bounds.
    switch kind {
    case .startOfSubject:
      builder.buildAssert { (input, pos, bounds) in
        pos == input.startIndex
      }

    case .endOfSubjectBeforeNewline:
      builder.buildAssert { (input, pos, bounds) in
        if pos == input.endIndex { return true }
        return input.index(after: pos) == input.endIndex
         && input[pos].isNewline
      }

    case .endOfSubject:
      builder.buildAssert { (input, pos, bounds) in
        pos == input.endIndex
      }

    case .resetStartOfMatch:
      // FIXME: Figure out how to communicate this out
      throw unsupported(#"\K (reset/keep assertion)"#)

    case .firstMatchingPositionInSubject:
      // TODO: We can probably build a nice model with API here
      builder.buildAssert { (input, pos, bounds) in
        pos == bounds.lowerBound
      }

    case .textSegment:
      // This we should be able to do!
      throw unsupported(#"\y (text segment)"#)

    case .notTextSegment:
      // This we should be able to do!
      throw unsupported(#"\Y (not text segment)"#)

    case .startOfLine:
      builder.buildAssert { (input, pos, bounds) in
        pos == input.startIndex ||
        input[input.index(before: pos)].isNewline
      }

    case .endOfLine:
      builder.buildAssert { (input, pos, bounds) in
        pos == input.endIndex || input[pos].isNewline
      }

    case .wordBoundary:
      // TODO: May want to consider Unicode level
      builder.buildAssert { (input, pos, bounds) in
        // TODO: How should we handle bounds?
        CharacterClass.word.isBoundary(
          input, at: pos, bounds: bounds)
      }

    case .notWordBoundary:
      // TODO: May want to consider Unicode level
      builder.buildAssert { (input, pos, bounds) in
        // TODO: How should we handle bounds?
        !CharacterClass.word.isBoundary(
          input, at: pos, bounds: bounds)
      }
    }
  }