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

Author: nicolasstucki

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

@@ -550,8 +550,14 @@ object Parsers {
       }
 
     /** Accept identifier and return Ident with its name as a term name. */
-    def termIdent(): Ident = atSpan(in.offset) {
-      makeIdent(in.token, ident())
+    def termIdent(): Ident = {
+      val lastOffset = in.lastOffset
+      val id = atSpan(in.offset) {
+        makeIdent(in.token, ident())
+      }
+      // Make sure that even trees with parsing errors have a offset that is within the offset
+      if (id.name == nme.ERROR && id.span == NoSpan) atSpan(lastOffset - 1)(id)
+      else id
     }
 
     /** 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

tests/neg/namedTypeParams.scala

@@ -11,7 +11,7 @@ object Test {
 
   def f[X, Y](x: X, y: Y): Int = ???
 
-  f[X = Int, String](1, "") // error // error
+  f[X = Int, String](1, "") // error: ']' expected, but `=` found
   f[X = Int][X = Int][Y = String](1, "") // error: illegal repeated type application
 
   f[X = Int][Y = String](1, "") // error: illegal repeated type application