Add SwiftWasm support (#363)

Author: yonihemi

Sources/ArgumentParser/Completions/CompletionsGenerator.swift

@@ -15,6 +15,8 @@ import Glibc
 import Darwin
 #elseif canImport(CRT)
 import CRT
+#elseif canImport(WASILibc)
+import WASILibc
 #endif
 
 /// A shell for which the parser can generate a completion script.

Sources/ArgumentParser/Parsable Properties/Errors.swift

@@ -15,6 +15,8 @@ import Glibc
 import Darwin
 #elseif canImport(CRT)
 import CRT
+#elseif canImport(WASILibc)
+import WASILibc
 #endif
 
 #if os(Windows)
@@ -66,6 +68,8 @@ public struct ExitCode: Error, RawRepresentable, Hashable {
   /// An exit code that indicates that the user provided invalid input.
 #if os(Windows)
   public static let validationFailure = ExitCode(ERROR_BAD_ARGUMENTS)
+#elseif os(WASI)
+  public static let validationFailure = ExitCode(EXIT_FAILURE)
 #else
   public static let validationFailure = ExitCode(EX_USAGE)
 #endif

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -18,6 +18,8 @@ let _exit: (Int32) -> Never = Darwin.exit
 #elseif canImport(CRT)
 import CRT
 let _exit: (Int32) -> Never = ucrt._exit
+#elseif canImport(WASILibc)
+import WASILibc
 #endif
 
 /// A type that can be parsed from a program's command-line arguments.

Sources/ArgumentParser/Usage/HelpGenerator.swift

@@ -348,7 +348,10 @@ import WinSDK
 #endif
 
 func _terminalSize() -> (width: Int, height: Int) {
-#if os(Windows)
+#if os(WASI)
+  // WASI doesn't yet support terminal size
+  return (80, 25)
+#elseif os(Windows)
   var csbi: CONSOLE_SCREEN_BUFFER_INFO = CONSOLE_SCREEN_BUFFER_INFO()
 
   GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi)