Improve script cli diagnostics

compiler/testData/cli/jvm/nonexistentScript.out

@@ -1,2 +1,2 @@
-error: source file or directory not found: path/to/nonexistent.kts
+error: script file not found: path/to/nonexistent.kts; Specify path to the script file as the first argument
 COMPILATION_ERROR

compiler/testData/cli/jvm/wrongScriptWithDirectory.out

@@ -1,2 +1,2 @@
-error: specify path to the script file as the first argument
+error: script argument points to a directory: $TESTDATA_DIR$/wrongAbiVersionLib; Specify path to the script file as the first argument
 COMPILATION_ERROR

compiler/testData/cli/jvm/wrongScriptWithKtSource.out

@@ -1,2 +1,2 @@
-error: specify path to the script file as the first argument
+error: unrecognized script file: $TESTDATA_DIR$/simple.kt; Specify path to the script file as the first argument
 COMPILATION_ERROR

plugins/scripting/scripting-compiler/src/org/jetbrains/kotlin/scripting/compiler/plugin/AbstractScriptEvaluationExtension.kt

@@ -60,11 +60,17 @@ abstract class AbstractScriptEvaluationExtension : ScriptEvaluationExtension {
                 val scriptFile = File(arguments.freeArgs.first())
                 val script = scriptFile.toScriptSource()
 
-                if (scriptFile.isDirectory || !scriptDefinitionProvider.isScript(script)) {
+                val error = when {
+                    !scriptFile.exists() -> "Script file not found: ${arguments.freeArgs.first()}"
+                    scriptFile.isDirectory  -> "Script argument points to a directory: ${arguments.freeArgs.first()}"
+                    !scriptDefinitionProvider.isScript(script) -> "Unrecognized script file: ${arguments.freeArgs.first()}"
+                    else -> null
+                }
+                if (error != null) {
                     val extensionHint =
                         if (configuration.get(ScriptingConfigurationKeys.SCRIPT_DEFINITIONS)?.let { it.size == 1 && it.first().isDefault } == true) " (.kts)"
                         else ""
-                    messageCollector.report(CompilerMessageSeverity.ERROR, "Specify path to the script file$extensionHint as the first argument")
+                    messageCollector.report(CompilerMessageSeverity.ERROR, "$error; Specify path to the script file$extensionHint as the first argument")
                     return ExitCode.COMPILATION_ERROR
                 }
                 script