Fix stability check for inline parameters

Inline parameters are not stable. Two references to the same parameter
may not be idempotent.

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

@@ -742,7 +742,7 @@ object SymDenotations {
       * So the first call to a stable member might fail and/or produce side effects.
       */
     final def isStableMember(using Context): Boolean = {
-      def isUnstableValue = isOneOf(UnstableValueFlags) || info.isInstanceOf[ExprType]
+      def isUnstableValue = isOneOf(UnstableValueFlags) || info.isInstanceOf[ExprType] || isAllOf(InlineParam)
       isType || is(StableRealizable) || exists && !isUnstableValue
     }
 

library/src/scala/quoted/Quotes.scala

@@ -14,7 +14,7 @@ import scala.reflect.TypeTest
  *  }
  *  ```
  */
-transparent inline def quotes(using inline q: Quotes): q.type = q
+transparent inline def quotes(using q: Quotes): q.type = q
 
 /** Quotation context provided by a macro expansion or in the scope of `scala.quoted.staging.run`.
  *  Used to perform all operations on quoted `Expr` or `Type`.

library/src/scala/runtime/stdLibPatches/Predef.scala

@@ -31,7 +31,7 @@ object Predef:
    *  @tparam T the type of the value to be summoned
    *  @return the given value typed: the provided type parameter
    */
-  transparent inline def summon[T](using inline x: T): x.type = x
+  transparent inline def summon[T](using inline x: T): T = x
 
   // Extension methods for working with explicit nulls
 

scaladoc/src/dotty/tools/scaladoc/tasty/TastyParser.scala

@@ -31,7 +31,7 @@ case class ScaladocTastyInspector()(using ctx: DocContext) extends DocTastyInspe
 
   def processCompilationUnit(using Quotes)(root: reflect.Tree): Unit = ()
 
-  override def postProcess(using Quotes): Unit =
+  override def postProcess(using q: Quotes): Unit =
     // hack into the compiler to get a list of all top-level trees
     // in principle, to do this, one would collect trees in processCompilationUnit
     // however, path-dependent types disallow doing so w/o using casts

scaladoc/src/dotty/tools/scaladoc/tasty/reflect.scala

@@ -4,4 +4,4 @@ package tasty
 import scala.quoted._
 
 /** Shorthand for `quotes.reflect` */
-transparent inline def reflect(using inline q: Quotes): q.reflect.type = q.reflect
+transparent inline def reflect(using q: Quotes): q.reflect.type = q.reflect

tests/neg/inline-param-unstable-path.scala

@@ -0,0 +1,6 @@
+inline val a = 3
+inline def f(inline x: Int, y: Int, z: => Int): Unit =
+  val x2: x.type = x // error: (x : Int) is not a valid singleton type, since it is not an immutable path
+  val y2: y.type = y
+  val z2: z.type = z // error: (z : Int) is not a valid singleton type, since it is not an immutable path
+  val a2: a.type = a