Performance: Eliminate Regex overhead in AvoidTrailingWhitespace -> Speedup of 5% (PowerShell 5.1) or 2.5 % (PowerShell 7.1-preview.2) (#1465)

* Improve performance by not using regex (2% improvement)

* replace regex

* fix index and simplify

* tidy

* Apply suggestions from code review

Co-Authored-By: Robert Holt <rjmholt@gmail.com>

* Use IsWhiteSpace

Co-authored-by: Christoph Bergmeister <christoph.bergmeister@bjss.com>
Co-authored-by: Robert Holt <rjmholt@gmail.com>

Author: 3 people

Rules/AvoidTrailingWhitespace.cs

@@ -36,52 +36,69 @@ public IEnumerable<DiagnosticRecord> AnalyzeScript(Ast ast, string fileName)
 
             var diagnosticRecords = new List<DiagnosticRecord>();
 
-            string[] lines = Regex.Split(ast.Extent.Text, @"\r?\n");
+            string[] lines = ast.Extent.Text.Split(new[] { "\r\n", "\r", "\n" }, StringSplitOptions.None);
 
             for (int lineNumber = 0; lineNumber < lines.Length; lineNumber++)
             {
                 var line = lines[lineNumber];
 
-                var match = Regex.Match(line, @"\s+$");
-                if (match.Success)
+                if (line.Length == 0)
                 {
-                    var startLine = lineNumber + 1;
-                    var endLine = startLine;
-                    var startColumn = match.Index + 1;
-                    var endColumn = startColumn + match.Length;
-
-                    var violationExtent = new ScriptExtent(
-                        new ScriptPosition(
-                            ast.Extent.File,
-                            startLine,
-                            startColumn,
-                            line
-                        ),
-                        new ScriptPosition(
-                            ast.Extent.File,
-                            endLine,
-                            endColumn,
-                            line
-                        ));
+                    continue;
+                }
 
-                    var suggestedCorrections = new List<CorrectionExtent>();
-                    suggestedCorrections.Add(new CorrectionExtent(
-                                violationExtent,
-                                string.Empty,
-                                ast.Extent.File
-                            ));
+                if (!char.IsWhiteSpace(line[line.Length - 1]) &&
+                    line[line.Length - 1] != '\t')
+                {
+                    continue;
+                }
 
-                    diagnosticRecords.Add(
-                        new DiagnosticRecord(
-                            String.Format(CultureInfo.CurrentCulture, Strings.AvoidTrailingWhitespaceError),
+                int startColumnOfTrailingWhitespace = 1;
+                for (int i = line.Length - 2; i > 0; i--)
+                {
+                    if (line[i] != ' ' && line[i] != '\t')
+                    {
+                        startColumnOfTrailingWhitespace = i + 2;
+                        break;
+                    }
+                }
+
+                int startLine = lineNumber + 1;
+                int endLine = startLine;
+                int startColumn = startColumnOfTrailingWhitespace;
+                int endColumn = line.Length + 1;
+
+                var violationExtent = new ScriptExtent(
+                    new ScriptPosition(
+                        ast.Extent.File,
+                        startLine,
+                        startColumn,
+                        line
+                    ),
+                    new ScriptPosition(
+                        ast.Extent.File,
+                        endLine,
+                        endColumn,
+                        line
+                    ));
+
+                var suggestedCorrections = new List<CorrectionExtent>();
+                suggestedCorrections.Add(new CorrectionExtent(
                             violationExtent,
-                            GetName(),
-                            GetDiagnosticSeverity(),
-                            ast.Extent.File,
-                            null,
-                            suggestedCorrections
+                            string.Empty,
+                            ast.Extent.File
                         ));
-                }
+
+                diagnosticRecords.Add(
+                    new DiagnosticRecord(
+                        String.Format(CultureInfo.CurrentCulture, Strings.AvoidTrailingWhitespaceError),
+                        violationExtent,
+                        GetName(),
+                        GetDiagnosticSeverity(),
+                        ast.Extent.File,
+                        null,
+                        suggestedCorrections
+                    ));
             }
 
             return diagnosticRecords;