Prohibit selection of tuples with members named apply. (#24191)

Similar to #24188, but we now disallow `apply` members at tuple
selection instead of tuple formation. This also works for hand-rolled
tuples built using `NamedTuple(...)`. And it constitutes the minimal fix
to avoid the recursion.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -850,11 +850,18 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       val namedTupleElems = qual.tpe.widenDealias.namedTupleElementTypes(true)
       val nameIdx = namedTupleElems.indexWhere(_._1 == selName)
       if nameIdx >= 0 && sourceVersion.enablesNamedTuples then
-        typed(
-          untpd.Apply(
-            untpd.Select(untpd.TypedSplice(qual), nme.apply),
-            untpd.Literal(Constant(nameIdx))),
-          pt)
+        if namedTupleElems.forall(_._1 != nme.apply) then
+          typed(
+            untpd.Apply(
+              untpd.Select(untpd.TypedSplice(qual), nme.apply),
+              untpd.Literal(Constant(nameIdx))),
+            pt)
+        else
+          report.error(
+            em"""Named tuples that define an `apply` field do not allow field selection.
+                |The `apply` field should be renamed to something else.""",
+            tree0.srcPos)
+          EmptyTree
       else EmptyTree
 
     // Otherwise, map combinations of A *: B *: .... EmptyTuple with nesting levels <= 22

tests/neg/named-tuple-apply.check

@@ -0,0 +1,28 @@
+-- Error: tests/neg/named-tuple-apply.scala:5:2 ------------------------------------------------------------------------
+5 |  (apply = () => 1)(())  // error // error
+  |  ^^^^^^^^^^^^^^^^^
+  |  Named tuples that define an `apply` field do not allow field selection.
+  |  The `apply` field should be renamed to something else.
+-- [E007] Type Mismatch Error: tests/neg/named-tuple-apply.scala:5:20 --------------------------------------------------
+5 |  (apply = () => 1)(())  // error // error
+  |                    ^^
+  |                    Found:    Unit
+  |                    Required: Int
+  |
+  | longer explanation available when compiling with `-explain`
+-- Error: tests/neg/named-tuple-apply.scala:6:29 -----------------------------------------------------------------------
+6 |  (apply = () => 1, foo = 2).foo  // error
+  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |  Named tuples that define an `apply` field do not allow field selection.
+  |  The `apply` field should be renamed to something else.
+-- Error: tests/neg/named-tuple-apply.scala:7:29 -----------------------------------------------------------------------
+7 |  (apply = () => 1, foo = 2).apply(1)  // error
+  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |  Named tuples that define an `apply` field do not allow field selection.
+  |  The `apply` field should be renamed to something else.
+-- [E050] Type Error: tests/neg/named-tuple-apply.scala:10:2 -----------------------------------------------------------
+10 |  foo() // error (error message could be better)
+   |  ^^^
+   |  method apply in class Foo does not take parameters
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/named-tuple-apply.scala

@@ -0,0 +1,10 @@
+class Foo:
+  def apply: () => Int = () => 2
+
+def test =
+  (apply = () => 1)(())  // error // error
+  (apply = () => 1, foo = 2).foo  // error
+  (apply = () => 1, foo = 2).apply(1)  // error
+
+  val foo = Foo()
+  foo() // error (error message could be better)