Only allow characters and numbers in attributes

compiler/src/dotty/tools/dotc/core/tasty/AttributePickler.scala

@@ -18,6 +18,7 @@ object AttributePickler:
         for attribute <- attributes do
           val bytes = attribute.getBytes(StandardCharsets.UTF_8).nn
           val length = bytes.length
+          assert("[a-zA-Z0-9]+".r.matches(attribute), "Malformed attribute. Attribute must match [a-zA-Z0-9]+")
           buf.writeNat(length)
           buf.writeBytes(bytes, length)
   end pickleAttributes

compiler/src/dotty/tools/dotc/core/tasty/AttributeUnpickler.scala

@@ -16,6 +16,7 @@ class AttributeUnpickler(reader: TastyReader):
       val length = readNat()
       val bytes = readBytes(length)
       val attribute = new String(bytes, StandardCharsets.UTF_8)
+      assert("[a-zA-Z0-9]+".r.matches(attribute), "Malformed attribute. Attribute must match [a-zA-Z0-9]+")
       attributesBuilder += attribute
     }
     attributesBuilder.result()

tasty/src/dotty/tools/tasty/TastyFormat.scala

@@ -265,10 +265,13 @@ All elements of a position section are serialized as Ints
 
 Standard Section: "Comments" Comment*
 ```none
-  Comment       = Length Bytes LongInt      // Raw comment's bytes encoded as UTF-8, followed by the comment's coordinates.
+  Comment       = UTF8 LongInt              // Raw comment's bytes encoded as UTF-8, followed by the comment's coordinates.
 ```
 
-Standard Section: "Attributes" UTF8*
+Standard Section: "Attributes" Attribute*
+```none
+  Attribute     = UTF8                      // attributes match the regex [a-zA-Z0-9]+
+```
 
 **************************************************************************************/