Soften the requirements of the code to be a REPL command

Author: ileasile

build-plugin/common-dependencies/src/org/jetbrains/kotlinx/jupyter/common/commandsUtil.kt

@@ -1,9 +1,11 @@
 package org.jetbrains.kotlinx.jupyter.common
 
+private val replCommandRegex = Regex("""^([\r\n\t ]*\n)?:([A-Za-z0-9]*)[\n\t\r ]*$""")
+
 /**
  * If this function returns true for the [code], it will be interpreted as Jupyter REPL command
  */
-fun looksLikeReplCommand(code: String): Boolean = code.startsWith(":")
+fun looksLikeReplCommand(code: String): Boolean = replCommandRegex.matches(code)
 
 /**
  * Throws [IllegalArgumentException] in case [looksLikeReplCommand] returns false for [code]
@@ -22,6 +24,7 @@ fun assertLooksLikeReplCommand(code: String) {
  */
 fun replCommandOrNull(code: String): Pair<ReplCommand?, String> {
     assertLooksLikeReplCommand(code)
-    val commandString = code.trim().substring(1)
+    val match = replCommandRegex.matchEntire(code)!!
+    val commandString = match.groupValues[2]
     return ReplCommand.valueOfOrNull(commandString)?.value to commandString
 }

src/test/kotlin/org/jetbrains/kotlinx/jupyter/test/CommandsTest.kt

@@ -0,0 +1,49 @@
+package org.jetbrains.kotlinx.jupyter.test
+
+import org.jetbrains.kotlinx.jupyter.common.looksLikeReplCommand
+import org.jetbrains.kotlinx.jupyter.common.replCommandOrNull
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class CommandsTest {
+    private fun assertLooksLikeReplCommand(expectedValid: Boolean, code: String) {
+        val actualValid = looksLikeReplCommand(code)
+        val expectedValidString = if (expectedValid) "valid" else "invalid"
+        assertEquals(expectedValid, actualValid, "Validation failed for code \"$code\", expected it to be $expectedValidString command")
+    }
+
+    private fun assertIsCommand(code: String, expectedCommandValue: String) {
+        assertLooksLikeReplCommand(true, code)
+        val actualCommandValue = replCommandOrNull(code).second
+        assertEquals(expectedCommandValue, actualCommandValue)
+    }
+
+    private fun assertNotCommand(code: String) = assertLooksLikeReplCommand(false, code)
+
+    @Test
+    fun `one-line command`() = assertIsCommand(":help", "help")
+
+    @Test
+    fun `command on the third line`() = assertIsCommand("\n:vars", "vars")
+
+    @Test
+    fun `command with the spaces on the first lines`() = assertIsCommand("\t\n  \n:myCommand", "myCommand")
+
+    @Test
+    fun `command with the spaces and newlines after it`() = assertIsCommand(":command \n   \t\n", "command")
+
+    @Test
+    fun `command with digits`() = assertIsCommand(":usefulCommand42", "usefulCommand42")
+
+    @Test
+    fun `command is tolerant to Windows newlines`() = assertIsCommand("\r  \r\n:windows ", "windows")
+
+    @Test
+    fun `command should not be split from the colon`() = assertNotCommand(": help")
+
+    @Test
+    fun `no valuable characters should appear in the command code`() = assertNotCommand(":my command")
+
+    @Test
+    fun `colon should be the first character in line`() = assertNotCommand(" :notHelp")
+}