Fix SIOOBE in Name#pos for substrings of length 1

Author: retronym

src/reflect/scala/reflect/internal/Names.scala

@@ -296,11 +296,13 @@ trait Names extends api.Names {
      */
     final def pos(s: String, start: Int): Int = {
       var i = pos(s.charAt(0), start)
-      while (i + s.length() <= len) {
+      val sLen = s.length()
+      if (sLen == 1) return i
+      while (i + sLen <= len) {
         var j = 1
         while (s.charAt(j) == chrs(index + i + j)) {
           j += 1
-          if (j == s.length()) return i
+          if (j == sLen) return i
         }
         i = pos(s.charAt(0), i + 1)
       }

test/junit/scala/reflect/internal/NamesTest.scala

@@ -92,4 +92,29 @@ class NamesTest {
     assert(h1 string_== h2)
     assert(h1 string_== h1y)
   }
+
+  @Test
+  def pos(): Unit = {
+    def check(nameString: String, sub: String) = {
+      val name = TermName(nameString)
+      val javaResult = name.toString.indexOf(sub) match { case -1 => name.length case x => x }
+      val nameResult = name.pos(sub)
+      assertEquals(javaResult, nameResult)
+      if (sub.length == 1) {
+        val nameResultChar = name.pos(sub.head)
+        assertEquals(javaResult, nameResultChar)
+      }
+    }
+
+    check("a", "a") // was "String index out of range: 1
+    check("a", "b")
+    check("a", "ab")
+    check("a", "ba")
+    check("ab", "a")
+    check("ab", "b")
+    check("ab", "ab")
+    check("ab", "ba")
+    check("", "x")
+    check("", "xy")
+  }
 }