Review fixes

- correctly check diffs in 'convert to named lambda parameter' code
  action tests
- add a fallback for empty names in type based term name inference

Author: KacperFKorban

presentation-compiler/src/main/dotty/tools/pc/utils/TermNameInference.scala

@@ -7,25 +7,28 @@ object TermNameInference {
 
   /** Single character names for types. (`Int` => `i`, `i1`, `i2`, ...) */
   def singleLetterNameStream(typeName: String): LazyList[String] = {
-    val typeName1 = sanitizeInput(typeName)
-    val firstCharStr = typeName1.headOption.getOrElse('x').toLower.toString
-    numberedStreamFromName(firstCharStr)
+    sanitizeInput(typeName).fold(saneNamesStream) { typeName1 =>
+      val firstCharStr = typeName1.headOption.getOrElse('x').toLower.toString
+      numberedStreamFromName(firstCharStr)
+    }
   }
 
   /** Names only from upper case letters (`OnDemandSymbolIndex` => `odsi`, `odsi1`, `odsi2`, ...) */
   def shortNameStream(typeName: String): LazyList[String] = {
-    val typeName1 = sanitizeInput(typeName)
-    val upperCases = typeName1.filter(_.isUpper).map(_.toLower)
-    val name = if (upperCases.isEmpty) typeName1 else upperCases
-    numberedStreamFromName(name)
+    sanitizeInput(typeName).fold(saneNamesStream) { typeName1 =>
+      val upperCases = typeName1.filter(_.isUpper).map(_.toLower)
+      val name = if (upperCases.isEmpty) typeName1 else upperCases
+      numberedStreamFromName(name)
+    }
   }
 
   /** Names from lower case letters (`OnDemandSymbolIndex` => `onDemandSymbolIndex`, `onDemandSymbolIndex1`, ...) */
   def fullNameStream(typeName: String): LazyList[String] = {
-    val typeName1 = sanitizeInput(typeName)
-    val withFirstLower =
-      typeName1.headOption.map(_.toLower).getOrElse('x').toString + typeName1.drop(1)
-    numberedStreamFromName(withFirstLower)
+    sanitizeInput(typeName).fold(saneNamesStream) { typeName1 =>
+      val withFirstLower =
+        typeName1.headOption.map(_.toLower).getOrElse('x').toString + typeName1.drop(1)
+      numberedStreamFromName(withFirstLower)
+    }
   }
 
   /** A lazy list of names: a, b, ..., z, aa, ab, ..., az, ba, bb, ... */
@@ -42,8 +45,9 @@ object TermNameInference {
     loop("a")
   }
 
-  private def sanitizeInput(typeName: String): String =
-    typeName.filter(_.isLetterOrDigit)
+  private def sanitizeInput(typeName: String): Option[String] =
+    val typeName1 = typeName.filter(_.isLetterOrDigit)
+    Option.when(typeName1.nonEmpty)(typeName1)
 
   private def numberedStreamFromName(name: String): LazyList[String] = {
     val rest = LazyList.from(1).map(name + _)

presentation-compiler/test/dotty/tools/pc/tests/edit/ConvertToNamedLambdaParametersSuite.scala

@@ -156,7 +156,7 @@ class ConvertToNamedLambdaParametersSuite extends BaseCodeActionSuite:
     val edits = convertToNamedLambdaParameters(original)
     val (code, _, _) = params(original)
     val obtained = TextEdits.applyEdits(code, edits)
-    assertNoDiff(obtained, obtained)
+    assertNoDiff(expected, obtained)
 
   def convertToNamedLambdaParameters(
       original: String,