Fix scala#5032: Make sure that erroneous empty idents have a position

Author: nicolasstucki

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -543,8 +543,12 @@ object Parsers {
       }
 
     /** Accept identifier and return Ident with its name as a term name. */
-    def termIdent(): Ident = atPos(in.offset) {
-      makeIdent(in.token, ident())
+    def termIdent(): Ident = {
+      // Make sure that even trees with parsing errors have a offset that is within the offset
+      val offset = if (in.offset <= in.lastOffset) in.offset else in.lastOffset - 1
+      atPos(offset) {
+        makeIdent(in.token, ident())
+      }
     }
 
     /** Accept identifier and return Ident with its name as a type name. */

tests/neg/i5032a.scala

@@ -0,0 +1,2 @@
+class i1@
+// error

tests/neg/i5032b.scala

@@ -0,0 +1,2 @@
+class a@
+class b@ // error // error