Add search functionality to the built-in help command

Sources/ArgumentParser/CMakeLists.txt

@@ -35,6 +35,7 @@ add_library(ArgumentParser
   Parsing/ParserError.swift
   Parsing/SplitArguments.swift
 
+  Usage/CommandSearcher.swift
   Usage/DumpHelpGenerator.swift
   Usage/HelpCommand.swift
   Usage/HelpGenerator.swift
@@ -49,7 +50,7 @@ add_library(ArgumentParser
   Utilities/StringExtensions.swift
   Utilities/SwiftExtensions.swift
   Utilities/Tree.swift
-  
+
   Validators/CodingKeyValidator.swift
   Validators/NonsenseFlagsValidator.swift
   Validators/ParsableArgumentsValidation.swift

Sources/ArgumentParser/Completions/CompletionsGenerator.swift

@@ -152,74 +152,6 @@ extension String {
     self.replacing("-", with: "_")
   }
 
-  func replacing(_ old: Self, with new: Self) -> Self {
-    guard !old.isEmpty else { return self }
-
-    var result = ""
-    var startIndex = self.startIndex
-
-    // Look for occurrences of the old string.
-    while let matchRange = self.firstMatch(of: old, at: startIndex) {
-      // Add the substring before the match.
-      result.append(contentsOf: self[startIndex..<matchRange.start])
-
-      // Add the replacement string.
-      result.append(contentsOf: new)
-
-      // Move past the matched portion.
-      startIndex = matchRange.end
-    }
-
-    // No more matches found, add the rest of the string.
-    result.append(contentsOf: self[startIndex..<self.endIndex])
-
-    return result
-  }
-
-  func firstMatch(
-    of match: Self,
-    at startIndex: Self.Index
-  ) -> (start: Self.Index, end: Self.Index)? {
-    guard !match.isEmpty else { return nil }
-    guard match.count <= self.count else { return nil }
-
-    var startIndex = startIndex
-    while startIndex < self.endIndex {
-      // Check if theres a match.
-      if let endIndex = self.matches(match, at: startIndex) {
-        // Return the match.
-        return (startIndex, endIndex)
-      }
-
-      // Move to the next of index.
-      self.formIndex(after: &startIndex)
-    }
-
-    return nil
-  }
-
-  func matches(
-    _ match: Self,
-    at startIndex: Self.Index
-  ) -> Self.Index? {
-    var selfIndex = startIndex
-    var matchIndex = match.startIndex
-
-    while true {
-      // Only continue checking if there is more match to check
-      guard matchIndex < match.endIndex else { return selfIndex }
-
-      // Exit early if there is no more "self" to check.
-      guard selfIndex < self.endIndex else { return nil }
-
-      // Check match and self are the the same.
-      guard self[selfIndex] == match[matchIndex] else { return nil }
-
-      // Move to the next pair of indices.
-      self.formIndex(after: &selfIndex)
-      match.formIndex(after: &matchIndex)
-    }
-  }
 }
 
 extension CommandInfoV0 {