Add Refactoring Action to Format Raw String Delimiters

Add a refactoring action that inserts or removes the appropriate
number of # delimiter characters to properly escape the content
of a string literal.

Author: CodaFi

Sources/SwiftRefactor/FormatRawStringLiteral.swift

@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+
+/// Format a string literal by inserting or removing the appropriate number of
+/// raw string `#` delimiters.
+///
+/// ## Before
+///
+/// ```swift
+/// "The # of values is \(count)"
+/// "Hello \#(world)"
+/// ###"Hello World"###
+/// ```
+///
+/// ## After
+///
+/// ```swift
+/// ##"The # of values is \(count)"##
+/// ##"Hello \#(world)"##
+/// "Hello World"
+/// ```
+public struct FormatRawStringLiteral: RefactoringProvider {
+  public static func refactor(syntax lit: StringLiteralExprSyntax, in context: Void) -> StringLiteralExprSyntax? {
+    var maximumHashes = 0
+    for segment in lit.segments {
+      switch segment {
+      case .expressionSegment(let expr):
+        if let delimiter = expr.delimiter {
+          // Pick up any delimiters in interpolation segments \#...#(...)
+          maximumHashes = max(maximumHashes, delimiter.text.longestRun(of: "#"))
+        }
+      case .stringSegment(let string):
+        // Find the longest run of # characters in the content of the literal.
+        maximumHashes = max(maximumHashes, string.content.text.longestRun(of: "#"))
+      }
+    }
+
+    guard maximumHashes > 0 else {
+      return lit
+        .withOpenDelimiter(lit.openDelimiter?.withKind(.rawStringDelimiter("")))
+        .withCloseDelimiter(lit.closeDelimiter?.withKind(.rawStringDelimiter("")))
+    }
+
+    let delimiters = String(repeating: "#", count: maximumHashes + 1)
+    return lit
+      .withOpenDelimiter(lit.openDelimiter?.withKind(.rawStringDelimiter(delimiters)))
+      .withCloseDelimiter(lit.closeDelimiter?.withKind(.rawStringDelimiter(delimiters)))
+  }
+}
+
+extension String {
+  fileprivate func longestRun(of needle: Character) -> Int {
+    var longest = 0
+    var it = self.makeIterator()
+    while let c = it.next() {
+      guard c == needle else {
+        continue
+      }
+
+      var localLongest = 1
+      while let c = it.next(), c == needle {
+        localLongest += 1
+        continue
+      }
+
+      longest = max(localLongest, longest)
+    }
+    return longest
+  }
+}

Tests/SwiftRefactorTest/FormatRawStringLiteral.swift

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftRefactor
+import SwiftSyntaxBuilder
+@_spi(RawSyntax) import SwiftSyntax
+@_spi(RawSyntax) import SwiftParser
+
+import XCTest
+import _SwiftSyntaxTestSupport
+
+final class FormatRawStringLiteralTest: XCTestCase {
+  func testDelimiterPlacement() throws {
+    let tests = [
+      (#line, literal: #" "Hello World" "#, expectation: #" "Hello World" "#),
+      (#line, literal: ##" #"Hello World" "##, expectation: #" "Hello World" "#),
+      (#line, literal: ##" #"Hello World"# "##, expectation: #" "Hello World" "#),
+      (#line, literal: #####" "####" "#####, expectation: #####" "####" "#####),
+      (#line, literal: #####" #"####"# "#####, expectation: ######" #####"####"##### "######),
+      (#line, literal: #####" #"\####(hello)"# "#####, expectation: ######" #####"\####(hello)"##### "######),
+      (#line, literal: #######" #"###### \####(hello) ##"# "#######, expectation: ########" #######"###### \####(hello) ##"####### "########),
+      (#line, literal: ########" #######"hello \(world) "####### "########, expectation: #" "hello \(world) " "#),
+    ]
+
+    for (line, literal, expectation) in tests {
+      let literal = try XCTUnwrap(StringLiteralExpr.parseWithoutDiagnostics(from: literal))
+      let expectation = try XCTUnwrap(StringLiteralExpr.parseWithoutDiagnostics(from: expectation))
+      let refactored = try XCTUnwrap(FormatRawStringLiteral.refactor(syntax: literal))
+      AssertStringsEqualWithDiff(refactored.description, expectation.description, line: UInt(line))
+    }
+  }
+}
+
+extension StringLiteralExpr {
+  static func parseWithoutDiagnostics(from string: String) -> StringLiteralExpr? {
+    var source = string
+    source.makeContiguousUTF8()
+    return source.withUTF8 { buffer in
+      var parser = Parser(buffer)
+      return parser.parseStringLiteral().syntax.as(StringLiteralExpr.self)
+    }
+  }
+}
+