Fix crash on ?Type

parser/src/main/kotlin/tools/samt/parser/Parser.kt

@@ -493,11 +493,21 @@ class Parser private constructor(
             check<OpenBraceToken>() -> parseObjectNode()
 
             skip<AsteriskToken>() -> WildcardNode(locationFromStart(start))
+            skip<QuestionMarkToken>() -> {
+                val literal = parseLiteral()
+                diagnostic.error {
+                    message("Nullability is indicated after a type")
+                    highlight(locationFromStart(start), highlightBeginningOnly = true)
+                    info("A valid nullable type looks like 'Int?' or 'String(size(1..*))?'")
+                    help("To declare the type nullable move the question mark to the end of the type")
+                }
+                literal
+            }
 
             else -> {
                 diagnostic.fatal {
                     message("Expected an expression")
-                    highlight(locationFromStart(start), highlightBeginningOnly = true)
+                    highlight(current!!.location, highlightBeginningOnly = true)
                 }
             }
         }

parser/src/test/kotlin/tools/samt/parser/ParserTest.kt

@@ -542,6 +542,17 @@ class ParserTest {
             val exception = parseWithFatalError(source)
             assertEquals("Expected an expression", exception.message)
         }
+
+        @Test
+        fun `unexpected question mark`() {
+            val source = """
+                package a
+
+                typealias A = ?String
+            """
+            val (_, diagnostics) = parseWithRecoverableError(source)
+            assertEquals("Nullability is indicated after a type", diagnostics.messages.single().message)
+        }
     }
 
     @Nested