Name stripped of module suffix must not be empty (#15597)

References #15381

Author: smarter

compiler/src/dotty/tools/dotc/core/NameOps.scala

@@ -124,10 +124,9 @@ object NameOps {
      *  it is also called from the backend.
      */
     def stripModuleClassSuffix: N = likeSpacedN {
-      val semName = name.toTermName match {
-        case name: SimpleName if name.endsWith("$") => name.unmangleClassName
+      val semName = name.toTermName match
+        case name: SimpleName if name.endsWith(str.MODULE_SUFFIX) && name.lastPart != MODULE_SUFFIX => name.unmangleClassName
         case _ => name
-      }
       semName.exclude(ModuleClassName)
     }
 

tests/neg/i15381.check

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/i15381.scala:5:13 -------------------------------------------------------------
+5 |def g: Int = $        // error
+  |             ^
+  |             Found:    $.type
+  |             Required: Int
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/i15381.scala

@@ -0,0 +1,11 @@
+// scalac: -Vprint:parser
+
+case class $[A](value: A)
+
+def g: Int = $        // error
+
+/*
+was:
+  |             Found:    .type
+  |             Required: Int
+ */