Add ensureApplied to the quotes reflect API

Author: jchyb

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -484,6 +484,8 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
           argss.foldLeft(self: Term)(Apply(_, _))
         def appliedToNone: Apply =
           self.appliedToArgs(Nil)
+        def ensureApplied: Term =
+          if (self.tpe.widen.isParameterless) self else self.appliedToNone
         def appliedToType(targ: TypeRepr): Term =
           self.appliedToTypes(targ :: Nil)
         def appliedToTypes(targs: List[TypeRepr]): Term =

library/src/scala/quoted/Quotes.scala

@@ -890,6 +890,9 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
         /** The current tree applied to (): `tree()` */
         def appliedToNone: Apply
 
+        /** The current tree applied to `()` unless the tree's widened type is parameterless */
+        def ensureApplied: Term
+
         /** The current tree applied to given type argument: `tree[targ]` */
         def appliedToType(targ: TypeRepr): Term
 

tests/pos-macros/i23969/Macro.scala

@@ -0,0 +1,26 @@
+
+import scala.quoted._
+
+object TestMethods:
+  def a1 = ()
+  def a2() = ()
+
+transparent inline def runMacro() = ${runMacroImpl}
+def runMacroImpl(using Quotes): Expr[Any] =
+  import quotes.reflect._
+
+  // ensureApplied test
+  Select.unique('{TestMethods}.asTerm, "a1").ensureApplied match
+    case Select(_, _) =>
+    case _ => assert(false)
+  Select.unique('{TestMethods}.asTerm, "a2").ensureApplied match
+    case Apply(_, _) =>
+    case _ => assert(false)
+
+  // regression test
+  val Inlined(_, _, generated) = '{BigDecimal(0).toString()}.asTerm : @unchecked
+  val Inlined(_, _, bigDecimal) = '{BigDecimal(0)}.asTerm : @unchecked
+  val custom = Select.unique(bigDecimal, "toString").ensureApplied
+  // ensure both have the same shape
+  assert(custom.toString == generated.toString)
+  custom.asExpr

tests/pos-macros/i23969/Main.scala

@@ -0,0 +1 @@
+@main def Test() = runMacro()