Simplify splitOptionPrefix implementation

Author: ajalt

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/mpp/MppH.kt

@@ -11,6 +11,4 @@ internal expect fun isWindowsMpp(): Boolean
 /** Doesn't return [Nothing], since it's a no-op on the browser */
 internal expect fun exitProcessMpp(status: Int)
 
-internal expect fun isLetterOrDigit(c: Char): Boolean
-
 internal expect fun readFileIfExists(filename: String): String?

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/parameters/options/Option.kt

@@ -1,8 +1,10 @@
 package com.github.ajalt.clikt.parameters.options
 
 import com.github.ajalt.clikt.completion.CompletionCandidates
-import com.github.ajalt.clikt.core.*
-import com.github.ajalt.clikt.mpp.isLetterOrDigit
+import com.github.ajalt.clikt.core.Context
+import com.github.ajalt.clikt.core.GroupableOption
+import com.github.ajalt.clikt.core.ParameterHolder
+import com.github.ajalt.clikt.core.StaticallyGroupedOption
 import com.github.ajalt.clikt.output.HelpFormatter
 import com.github.ajalt.clikt.parsers.Invocation
 import com.github.ajalt.clikt.sources.ValueSource
@@ -130,7 +132,7 @@ internal fun inferEnvvar(names: Set<String>, envvar: String?, autoEnvvarPrefix:
 /** Split an option token into a pair of prefix to simple name. */
 internal fun splitOptionPrefix(name: String): Pair<String, String> =
     when {
-        name.length < 2 || isLetterOrDigit(name[0]) -> "" to name
+        name.length < 2 || name[0] !in "-@/+" -> "" to name
         name.length > 2 && name[0] == name[1] -> name.slice(0..1) to name.substring(2)
         else -> name.substring(0, 1) to name.substring(1)
     }

clikt/src/jsMain/kotlin/com/github/ajalt/clikt/mpp/MppImpl.kt

@@ -35,12 +35,8 @@ private val impls: JsMppImpls = try {
     BrowserMppImpls
 }
 
-private val LETTER_OR_DIGIT_RE = Regex("""[a-zA-Z0-9]""")
-
 internal actual val String.graphemeLengthMpp: Int get() = replace(ANSI_CODE_RE, "").length
 
-internal actual fun isLetterOrDigit(c: Char): Boolean = LETTER_OR_DIGIT_RE.matches(c.toString())
-
 internal actual fun readEnvvar(key: String): String? = impls.readEnvvar(key)
 internal actual fun isWindowsMpp(): Boolean = impls.isWindowsMpp()
 internal actual fun exitProcessMpp(status: Int): Unit = impls.exitProcessMpp(status)

clikt/src/jvmMain/kotlin/com/github/ajalt/clikt/mpp/MppImpl.kt

@@ -18,10 +18,6 @@ internal actual fun exitProcessMpp(status: Int) {
     exitProcess(status)
 }
 
-internal actual fun isLetterOrDigit(c: Char): Boolean {
-    return c.isLetterOrDigit()
-}
-
 internal actual fun readFileIfExists(filename: String): String? {
     val file = File(filename)
     if (!file.isFile) return null

clikt/src/nativeMain/kotlin/com/github/ajalt/clikt/mpp/MppImpl.kt

@@ -9,12 +9,8 @@ import platform.posix.fopen
 import kotlin.experimental.ExperimentalNativeApi
 import kotlin.system.exitProcess
 
-private val LETTER_OR_DIGIT_RE = Regex("""[a-zA-Z0-9]""")
-
 internal actual val String.graphemeLengthMpp: Int get() = replace(ANSI_CODE_RE, "").length
 
-internal actual fun isLetterOrDigit(c: Char): Boolean = LETTER_OR_DIGIT_RE.matches(c.toString())
-
 internal actual fun isWindowsMpp(): Boolean = Platform.osFamily == OsFamily.WINDOWS
 
 internal actual fun exitProcessMpp(status: Int): Unit = exitProcess(status)