Function buildReplacementLines

agent/agentfiles/files.go:965–1077

buildReplacementLines emits the splice for a fuzzy match by per-position substitution at leading-ws, body, trailing-ws, and ending. Search and replace agreement at a position -> file's bytes win; disagreement -> replacement's bytes are spliced. Extra replace lines past the matched region reference t

(matched, searchLines []string, replace, forcedEnding string, atNoNewlineEOF bool)

//
//nolint:revive // atNoNewlineEOF is a computed match property, not caller control coupling.
func buildReplacementLines(matched, searchLines []string, replace, forcedEnding string, atNoNewlineEOF bool) string {
	repLines := strings.SplitAfter(replace, "\n")
	// SplitAfter on a string ending in "\n" yields a trailing empty
	// element. Drop it so it doesn't pair with a phantom line.
	if len(repLines) > 0 && repLines[len(repLines)-1] == "" {
		repLines = repLines[:len(repLines)-1]
	}
	prefix, suffix := alignSearchReplace(searchLines, repLines)

	// Combine search and replace so a zero-width search still
	// informs the unit from the replacement's inserted depths.
	// Fallback for detection failure lives in the inserted branch.
	searchUnit, searchUnitOK := detectIndentUnit(append(append([]string(nil), searchLines...), repLines...))
	fileUnit, fileUnitOK := detectIndentUnit(matched)
	var b strings.Builder
	for i, rLine := range repLines {
		var refIdx int
		inserted := false
		searchMiddleLen := len(searchLines) - prefix - suffix
		switch {
		case i < prefix:
			refIdx = i
		case i >= len(repLines)-suffix:
			refIdx = i - (len(repLines) - len(searchLines))
		case i-prefix < searchMiddleLen:
			refIdx = prefix + (i - prefix)
		default:
			// Pure insertion: pick the reference content line by
			// the caller's indent signal. An inserted line whose
			// lead matches the suffix's first rep line belongs to
			// the suffix scope; one matching the prefix's last rep
			// line belongs to the prefix scope. Fall back to
			// suffix, then prefix, then i-clamped.
			inserted = true
			rLeadForI := leadOnly(rLine)
			switch {
			case prefix > 0 && suffix > 0:
				prefixRLead := leadOnly(repLines[prefix-1])
				suffixRLead := leadOnly(repLines[len(repLines)-suffix])
				switch {
				case rLeadForI == suffixRLead:
					refIdx = len(searchLines) - suffix
				case rLeadForI == prefixRLead:
					refIdx = prefix - 1
				default:
					refIdx = len(searchLines) - suffix
				}
			case suffix > 0:
				refIdx = len(searchLines) - suffix
			case prefix > 0:
				refIdx = prefix - 1
			default:
				refIdx = min(i, len(searchLines)-1)
			}
		}
		refContent := matched[refIdx]
		sLead, _, sTrail, sEnd := splitLineParts(searchLines[refIdx])
		rLead, rMid, rTrail, rEnd := splitLineParts(rLine)