perf: fix ~50% regression in FindIncludesInContent (#21265)

Author: Copilot

pkg/cli/remove_command.go

@@ -1,7 +1,6 @@
 package cli
 
 import (
-	"bufio"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -391,9 +390,7 @@ func findIncludesInContent(content, baseDir string, verbose bool) ([]string, err
 	_ = verbose // unused parameter for now, keeping for potential future use
 	var includes []string
 
-	scanner := bufio.NewScanner(strings.NewReader(content))
-	for scanner.Scan() {
-		line := scanner.Text()
+	for line := range strings.Lines(content) {
 		directive := parser.ParseImportDirective(line)
 		if directive != nil {
 			includePath := directive.Path
@@ -411,5 +408,5 @@ func findIncludesInContent(content, baseDir string, verbose bool) ([]string, err
 		}
 	}
 
-	return includes, scanner.Err()
+	return includes, nil // strings.Lines iterates over an in-memory string; no I/O errors can occur.
 }

pkg/parser/import_directive.go

@@ -28,14 +28,20 @@ type ImportDirectiveMatch struct {
 func ParseImportDirective(line string) *ImportDirectiveMatch {
 	trimmedLine := strings.TrimSpace(line)
 
+	// Fast-path: import directives must start with '@' or '{'; skip the regex for all other lines.
+	if len(trimmedLine) == 0 || (trimmedLine[0] != '@' && trimmedLine[0] != '{') {
+		return nil
+	}
+
 	// Check if it matches the import pattern at all
 	matches := IncludeDirectivePattern.FindStringSubmatch(trimmedLine)
 	if matches == nil {
 		return nil
 	}
 
-	// Check if it's legacy syntax
-	isLegacy := LegacyIncludeDirectivePattern.MatchString(trimmedLine)
+	// Determine legacy vs new syntax from the captured groups of the first match.
+	// Group 2 (path for @include/@import) is non-empty iff the legacy alternative matched.
+	isLegacy := matches[2] != ""
 	importDirectiveLog.Printf("Parsing import directive: legacy=%t, line=%s", isLegacy, trimmedLine)
 
 	var isOptional bool