dollar-slash string can be the first lexeme of file

plugins/groovy/src/org/jetbrains/plugins/groovy/lang/lexer/groovy.flex

@@ -664,6 +664,9 @@ mGSTRING_LITERAL = \"\"
 
 {mGSTRING_LITERAL}                                         {  return mGSTRING_LITERAL; }
 
+"$""/"                                                     {  yypushback(2);
+                                                              yybegin(WAIT_FOR_REGEX); }
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 ///////////////////////// keywords /////////////////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

plugins/groovy/test/org/jetbrains/plugins/groovy/lang/parser/ExpressionsParsingTest.groovy

@@ -157,6 +157,8 @@ public class ExpressionsParsingTest extends GroovyParsingTestCase {
   public void testregex$regex18() throws Throwable { doTest(); }
   public void testregex$regex19() throws Throwable { doTest(); }
   public void testregex$regex2() throws Throwable { doTest(); }
+  public void testregex$regex20() throws Throwable { doTest(); }
+  public void testregex$regex21() throws Throwable { doTest(); }
   public void testregex$regex3() throws Throwable { doTest(); }
   public void testregex$regex33() throws Throwable { doTest(); }
   public void testregex$regex4() throws Throwable { doTest(); }

plugins/groovy/testdata/parsing/groovy/expressions/regex/regex20.test

@@ -0,0 +1,14 @@
+print (/a\${2}/)
+-----
+Groovy script
+  Method call
+    Reference expression
+      PsiElement(identifier)('print')
+    PsiWhiteSpace(' ')
+    Arguments
+      PsiElement(()('(')
+      Compound regular expression
+        PsiElement(regex begin)('/')
+        PsiElement(regex content)('a\${2}')
+        PsiElement(regex end)('/')
+      PsiElement())(')')

plugins/groovy/testdata/parsing/groovy/expressions/regex/regex21.test

@@ -0,0 +1,7 @@
+$/abc/$
+-----
+Groovy script
+  Compound regular expression
+    PsiElement($/ regex begin)('$/')
+    PsiElement($/ regex content)('abc')
+    PsiElement($/ regex end)('/$')