tests: Only toolArgsParse the first 10 lines

Author: dwijnand

compiler/test/dotty/tools/utils.scala

@@ -45,7 +45,7 @@ def assertThrows[T <: Throwable: ClassTag](p: T => Boolean)(body: => Any): Unit
 end assertThrows
 
 def toolArgsFor(files: List[JPath])(using codec: Codec = Codec.UTF8): List[String] =
-  files.flatMap(path => toolArgsParse(readLines(path.toFile)))
+  files.flatMap(path => toolArgsParse(withFile(path.toFile)(_.getLines().take(10).toList)))
 
 // Inspect the first 10 of the given lines for compiler options of the form
 // `// scalac: args`, `/* scalac: args`, ` * scalac: args`.
@@ -57,7 +57,8 @@ def toolArgsParse(lines: List[String]): List[String] = {
   val endc = "*" + "/"    // be forgiving of /* scalac: ... */
   def stripped(s: String) = s.substring(s.indexOf(tag) + tag.length).stripSuffix(endc)
   val args = lines.to(LazyList).take(10).filter { s =>
-       s.contains("// " + tag)
+       s.contains("//" + tag)
+    || s.contains("// " + tag)
     || s.contains("/* " + tag)
     || s.contains(" * " + tag)
     // but avoid picking up comments like "% scalac ./a.scala" and "$ scalac a.scala"