Add logic to split command line arguments on Windows

Previously, we were splitting command line arguments on Windows using the same rules as on Unix, which was incorrect, most importantly because backslashes in the first component of a Windows command line invocation are not escaping anything but interpreted verbatim.

Fixes #1020
rdar://120809063

Author: ahoppen

Sources/SKCore/CMakeLists.txt

@@ -11,6 +11,7 @@ add_library(SKCore STATIC
   FileBuildSettings.swift
   MainFilesProvider.swift
   PathPrefixMapping.swift
+  SplitShellCommand.swift
   Toolchain.swift
   ToolchainRegistry.swift
   XCToolchainPlist.swift)

Sources/SKCore/CompilationDatabase.swift

@@ -251,7 +251,11 @@ extension CompilationDatabase.Command: Codable {
     if let arguments = try container.decodeIfPresent([String].self, forKey: .arguments) {
       self.commandLine = arguments
     } else if let command = try container.decodeIfPresent(String.self, forKey: .command) {
+      #if os(Windows)
+      self.commandLine = splitWindowsCommandLine(command, initialCommandName: true)
+      #else
       self.commandLine = splitShellEscapedCommand(command)
+      #endif
     } else {
       throw CompilationDatabaseDecodingError.missingCommandOrArguments
     }
@@ -265,123 +269,3 @@ extension CompilationDatabase.Command: Codable {
     try container.encodeIfPresent(output, forKey: .output)
   }
 }
-
-/// Split and unescape a shell-escaped command line invocation.
-///
-/// Examples:
-///
-/// ```
-/// abc def -> ["abc", "def"]
-/// abc\ def -> ["abc def"]
-/// abc"\""def -> ["abc\"def"]
-/// abc'\"'def -> ["abc\\"def"]
-/// ```
-///
-/// See clang's `unescapeCommandLine()`.
-public func splitShellEscapedCommand(_ cmd: String) -> [String] {
-  struct Parser {
-    var content: Substring
-    var i: Substring.UTF8View.Index
-    var result: [String] = []
-
-    var ch: UInt8 { self.content.utf8[i] }
-    var done: Bool { self.content.endIndex == i }
-
-    init(_ string: Substring) {
-      self.content = string
-      self.i = self.content.utf8.startIndex
-    }
-
-    mutating func next() {
-      i = content.utf8.index(after: i)
-    }
-
-    mutating func next(expect c: UInt8) {
-      assert(c == ch)
-      next()
-    }
-
-    mutating func parse() -> [String] {
-      while !done {
-        switch ch {
-        case UInt8(ascii: " "): next()
-        default: parseString()
-        }
-      }
-      return result
-    }
-
-    mutating func parseString() {
-      var str = ""
-      STRING: while !done {
-        switch ch {
-        case UInt8(ascii: " "): break STRING
-        case UInt8(ascii: "\""): parseDoubleQuotedString(into: &str)
-        case UInt8(ascii: "\'"): parseSingleQuotedString(into: &str)
-        default: parsePlainString(into: &str)
-        }
-      }
-      result.append(str)
-    }
-
-    mutating func parseDoubleQuotedString(into str: inout String) {
-      next(expect: UInt8(ascii: "\""))
-      var start = i
-      while !done {
-        switch ch {
-        case UInt8(ascii: "\""):
-          str += content[start..<i]
-          next()
-          return
-        case UInt8(ascii: "\\"):
-          str += content[start..<i]
-          next()
-          start = i
-          if !done { fallthrough }
-        default:
-          next()
-        }
-      }
-      str += content[start..<i]
-    }
-
-    mutating func parseSingleQuotedString(into str: inout String) {
-      next(expect: UInt8(ascii: "\'"))
-      let start = i
-      while !done {
-        switch ch {
-        case UInt8(ascii: "\'"):
-          str += content[start..<i]
-          next()
-          return
-        default:
-          next()
-        }
-      }
-      str += content[start..<i]
-    }
-
-    mutating func parsePlainString(into str: inout String) {
-      var start = i
-      while !done {
-        let _ch = ch
-        switch _ch {
-        case UInt8(ascii: "\""), UInt8(ascii: "\'"), UInt8(ascii: " "):
-          str += content[start..<i]
-          return
-        case UInt8(ascii: "\\"):
-          str += content[start..<i]
-          next()
-          start = i
-          if !done { fallthrough }
-        default:
-          next()
-        }
-      }
-      str += content[start..<i]
-    }
-  }
-
-  var parser = Parser(cmd[...])
-  return parser.parse()
-}