[2.x] fix: Backtick-quote project IDs in classloader error messages (#8830)

When a test fails with ClassNotFoundException/IllegalAccessError, sbt
suggests a set command to change classLoaderLayeringStrategy. If the
project name contains hyphens (e.g. bug-report), the suggested command
was syntactically invalid because it parses as subtraction in Scala.

Quote project IDs using Util.quoteIfNotScalaId so the suggested
commands are valid when copy-pasted.

Fixes #5803

build.sbt

@@ -311,6 +311,7 @@ lazy val utilCore = project
     utilCommonSettings,
     name := "Util Core",
     Utils.keywordsSettings,
+    libraryDependencies ++= Seq(hedgehog % Test),
     mimaSettings,
     mimaBinaryIssueFilters ++= Seq(
     ),

internal/util-core/src/main/scala/sbt/internal/util/Util.scala

@@ -45,6 +45,14 @@ object Util:
 
   def quoteIfKeyword(s: String): String = if (ScalaKeywords.values(s)) s"`${s}`" else s
 
+  def quoteIfNotScalaId(s: String): String =
+    if isValidScalaId(s) && !ScalaKeywords.values(s) then s
+    else s"`$s`"
+
+  private def isValidScalaId(s: String): Boolean =
+    s.nonEmpty && (s.charAt(0).isLetter || s.charAt(0) == '_') &&
+      s.forall(c => c.isLetterOrDigit || c == '_')
+
   def ignoreResult[A](f: => A): Unit = {
     val _ = f
     ()

internal/util-core/src/test/scala/sbt/internal/util/UtilSpec.scala

@@ -0,0 +1,49 @@
+/*
+ * sbt
+ * Copyright 2023, Scala center
+ * Copyright 2011 - 2022, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal.util
+
+import hedgehog.*
+import hedgehog.runner.*
+
+object UtilSpec extends Properties:
+  override def tests: List[Test] = List(
+    example(
+      "quoteIfNotScalaId should not quote simple identifiers",
+      assertQuote("foo", "foo"),
+    ),
+    example(
+      "quoteIfNotScalaId should not quote identifiers with underscores",
+      assertQuote("foo_bar", "foo_bar"),
+    ),
+    example(
+      "quoteIfNotScalaId should quote identifiers with hyphens",
+      assertQuote("bug-report", "`bug-report`"),
+    ),
+    example(
+      "quoteIfNotScalaId should quote identifiers with dots",
+      assertQuote("my.project", "`my.project`"),
+    ),
+    example(
+      "quoteIfNotScalaId should quote identifiers starting with digits",
+      assertQuote("123abc", "`123abc`"),
+    ),
+    example(
+      "quoteIfNotScalaId should quote Scala keywords",
+      assertQuote("class", "`class`"),
+    ),
+    example(
+      "quoteIfNotScalaId should quote empty strings",
+      assertQuote("", "``"),
+    ),
+  )
+
+  private def assertQuote(input: String, expected: String): Result =
+    val actual = Util.quoteIfNotScalaId(input)
+    Result.assert(actual == expected).log(s"input=$input expected=$expected actual=$actual")
+end UtilSpec

main/src/main/scala/sbt/Defaults.scala

@@ -1201,7 +1201,20 @@ object Defaults extends BuildCommon {
         thisProject,
         fileConverter,
       ).flatMapN { (s, lt, tl, gp, ex, cp, fp, jo, clls, thisProj, c) =>
-        allTestGroupsTask(s, lt, tl, gp, ex, cp, fp, fpm, jo, clls, s"${thisProj.id} / ", c)
+        allTestGroupsTask(
+          s,
+          lt,
+          tl,
+          gp,
+          ex,
+          cp,
+          fp,
+          fpm,
+          jo,
+          clls,
+          s"${Util.quoteIfNotScalaId(thisProj.id)} / ",
+          c
+        )
       }
     }.value),
     // ((streams in test, loadedTestFrameworks, testLoader, testGrouping in test, testExecution in test, fullClasspath in test, javaHome in test, testForkedParallel, javaOptions in test) flatMap allTestGroupsTask).value,
@@ -1377,7 +1390,7 @@ object Defaults extends BuildCommon {
         testForkedParallelism.value,
         javaOptions.value,
         classLoaderLayeringStrategy.value,
-        projectId = s"${thisProject.value.id} / ",
+        projectId = s"${Util.quoteIfNotScalaId(thisProject.value.id)} / ",
         converter = fileConverter.value,
       )
       val taskName = display.show(resolvedScoped.value)