[windows] fix trailing backslash string quoting (swiftlang#555)

Author: charles-zablit

.github/workflows/pull_request.yml

@@ -24,7 +24,7 @@ jobs:
       windows_swift_versions: '["nightly-main"]'
       windows_build_command: 'Invoke-Program swift build'
       enable_android_sdk_build: true
-      android_sdk_build_command: "swift build --build-tests"
+      android_sdk_build_command: "swift build --build-tests --build-system native"
       android_ndk_versions: '["r27d", "r29"]'
       enable_ios_checks: true
       enable_macos_checks: true

Sources/TSCBasic/StringConversions.swift

@@ -50,36 +50,53 @@ extension String {
     public func spm_shellEscaped() -> String {
 
         // If all the characters in the string are in the allow list then no need to escape.
-        guard let pos = utf8.firstIndex(where: { !inShellAllowlist($0) }) else {
+        guard utf8.contains(where: { !inShellAllowlist($0) }) else {
             return self
         }
 
-      #if os(Windows)
-        let quoteCharacter: Character = "\""
-        let escapedQuoteCharacter = "\"\""
-      #else
-        let quoteCharacter: Character = "'"
-        let escapedQuoteCharacter = "'\\''"
-      #endif
-        // If there are no quote characters then we can just wrap the string within the quotes.
-        guard let quotePos = utf8[pos...].firstIndex(of: quoteCharacter.asciiValue!) else {
-            return String(quoteCharacter) + self + String(quoteCharacter)
-        }
+        #if os(Windows)
+            var quoted = "\""
+            var unquoted = self.unicodeScalars
+            while !unquoted.isEmpty {
+                guard let firstNonBackslash = unquoted.firstIndex(where: { $0 != "\\" }) else {
+                    let backslashCount = unquoted.count
+                    quoted.append(String(repeating: "\\", count: backslashCount * 2))
+                    break
+                }
+                let backslashCount = unquoted.distance(
+                    from: unquoted.startIndex, to: firstNonBackslash)
+                if unquoted[firstNonBackslash] == "\"" {
+                    quoted.append(String(repeating: "\\", count: backslashCount * 2 + 1))
+                } else {
+                    quoted.append(String(repeating: "\\", count: backslashCount))
+                }
+                quoted.append(String(unquoted[firstNonBackslash]))
+                unquoted.removeFirst(backslashCount + 1)
+            }
+            quoted.append("\"")
+            return quoted
+        #else
+            let quoteCharacter: Character = "'"
+            let escapedQuoteCharacter = "'\\''"
+            // If there are no quote characters then we can just wrap the string within the quotes.
+            guard let quotePos = utf8.firstIndex(of: quoteCharacter.asciiValue!) else {
+                return String(quoteCharacter) + self + String(quoteCharacter)
+            }
 
-        // Otherwise iterate and escape all the single quotes.
-        var newString = String(quoteCharacter) + String(self[..<quotePos])
+            // Otherwise iterate and escape all the single quotes.
+            var newString = String(quoteCharacter) + String(self[..<quotePos])
 
-        for char in self[quotePos...] {
-            if char == quoteCharacter {
-                newString += escapedQuoteCharacter
-            } else {
-                newString += String(char)
+            for char in self[quotePos...] {
+                if char == quoteCharacter {
+                    newString += escapedQuoteCharacter
+                } else {
+                    newString += String(char)
+                }
             }
-        }
-
-        newString += String(quoteCharacter)
 
-        return newString
+            newString += String(quoteCharacter)
+            return newString
+        #endif
     }
 
     /// Shell escapes the current string. This method is mutating version of shellEscaped().

Tests/TSCBasicTests/StringConversionsTests.swift

@@ -36,6 +36,21 @@ class StringConversionTests: XCTestCase {
 
         str = "hello\nA\"B C>D*[$;()^><"
         XCTAssertEqual("'hello\nA\"B C>D*[$;()^><'", str.spm_shellEscaped())
+
+        #if os(Windows)
+        // Trailing backslash must be doubled so the closing quote is not escaped.
+        str = "hello world\\"
+        XCTAssertEqual("\"hello world\\\\\"", str.spm_shellEscaped())
+
+        // Embedded double-quote is escaped with a backslash.
+        str = "hello\"world"
+        XCTAssertEqual("\"hello\\\"world\"", str.spm_shellEscaped())
+
+        // Backslash immediately before an embedded double-quote: the backslash is doubled,
+        // then the quote is escaped with another backslash.
+        str = "hello\\\"world"
+        XCTAssertEqual("\"hello\\\\\\\"world\"", str.spm_shellEscaped())
+        #endif
     }
 
     func testLocalizedJoin() {