Fix stability check for inline parameters (scala#15511)

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

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

@@ -773,7 +773,7 @@ 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 x: T): x.type = x
 
   // Extension methods for working with explicit nulls
 

sbt-test/source-dependencies/inline-rec-change-inline/B.scala

@@ -1,5 +1,5 @@
 object B {
 
-  inline def inlinedAny(x: String): x.type = x
+  inline def inlinedAny(x: String): String = x
 
 }

sbt-test/source-dependencies/inline-rec-change-inline/changes/B1.scala

@@ -1,5 +1,5 @@
 object B {
 
-  inline def inlinedAny(inline x: String): x.type = x
+  inline def inlinedAny(inline x: String): String = x
 
 }

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

tests/neg/inline-val-in-inline-method.scala

@@ -0,0 +1,8 @@
+inline def f(inline x: Int): Unit =
+  inline val b = x
+  val c: b.type = b
+
+def test =
+  f(1)
+  def a = 1
+  f(a) // error: inline value must have a literal constant type

tests/pos/i11163.scala

@@ -1,12 +1,12 @@
 inline def summonA[T](using x: T): x.type = x
-inline def summonB[T](using inline x: T): x.type = x
+// inline def summonB[T](using inline x: T): x.type = x // inline parameters are unstable
 inline def summonC[T](using inline x: T): T = x
 
 trait Foo:
   def f: Int = 9
 
 def test(using Foo) =
   summonA[Foo].f
-  summonB[Foo].f
+  // summonB[Foo].f
   summonC[Foo].f
   ()

tests/pos/i12379a.scala

@@ -1,7 +1,7 @@
-inline def convFail[Of, From](inline from : From) : Unit =
+inline def convFail[Of, From](from : From) : Unit = // removed inline from parameter to avoid unsound path selection
   val c = compiletime.summonInline[Conversion[from.type, Of]]
 
-inline def convOK[Of, From](inline from : From)(using c : Conversion[from.type, Of]) : Unit = {}
+inline def convOK[Of, From](from : From)(using c : Conversion[from.type, Of]) : Unit = {} // removed inline from parameter to avoid unsound path selection
 
 class Bar[T](value : T)
 given [T <: Int] : Conversion[T, Bar[T]] = Bar(_)

tests/run/deriving-constructor-order.scala

@@ -2,7 +2,7 @@ import scala.compiletime.erasedValue
 import scala.deriving.Mirror
 
 object Test extends App {
-  inline def checkElems[A, T](using inline A: Mirror.SumOf[A]): Unit =
+  inline def checkElems[A, T](using A: Mirror.SumOf[A]): Unit = // removed inline from parameter to avoid unsound path selection
     inline erasedValue[A.MirroredElemTypes] match {
       case _: T => ()
     }