allow infix extension methods

Author: arainko

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

@@ -555,7 +555,9 @@ object Checking {
         fail(CannotHaveSameNameAs(sym, cls, CannotHaveSameNameAs.CannotBeOverridden))
         sym.setFlag(Private) // break the overriding relationship by making sym Private
       }
-    if sym.isWrappedToplevelDef && !sym.isType && sym.flags.is(Infix) then fail(ToplevelDefCantBeInfix(sym))
+
+    if sym.isWrappedToplevelDef && !sym.isType && sym.flags.is(Infix, butNot = Extension) then
+      fail(ToplevelDefCantBeInfix(sym))
     checkApplicable(Erased,
       !sym.isOneOf(MutableOrLazy, butNot = Given) && !sym.isType || sym.isClass)
     checkCombination(Final, Open)

tests/neg/i17738-toplevel-infix.check

@@ -1,20 +1,20 @@
--- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:10:10 ----------------------------------------------------
-10 |infix val toplevelVal = ??? // error
+-- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:13:10 ----------------------------------------------------
+13 |infix val toplevelVal = ??? // error
    |          ^
    |          a toplevel val cannot be infix
--- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:11:10 ----------------------------------------------------
-11 |infix var toplevelVar = ??? // error
+-- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:14:10 ----------------------------------------------------
+14 |infix var toplevelVar = ??? // error
    |          ^
    |          a toplevel var cannot be infix
--- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:12:10 ----------------------------------------------------
-12 |infix def toplevelDef = ??? // error
+-- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:15:10 ----------------------------------------------------
+15 |infix def toplevelDef = ??? // error
    |          ^
    |          a toplevel def cannot be infix
--- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:13:12 ----------------------------------------------------
-13 |infix given toplevelGiven: Int = ??? // error
+-- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:16:12 ----------------------------------------------------
+16 |infix given toplevelGiven: Int = ??? // error
    |            ^
    |            a toplevel given cannot be infix
--- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:14:19 ----------------------------------------------------
-14 |infix implicit val topevelImplicit: Int = ??? // error
+-- [E183] Syntax Error: tests/neg/i17738-toplevel-infix.scala:17:19 ----------------------------------------------------
+17 |infix implicit val topevelImplicit: Int = ??? // error
    |                   ^
    |                   a toplevel val cannot be infix

tests/neg/i17738-toplevel-infix.scala

@@ -7,6 +7,9 @@ infix type B[b, a] = b match {
 infix class C[A, B]
 infix trait D[A, B]
 
+extension (x: Boolean)
+  infix def or (y: => Boolean) = x || y
+
 infix val toplevelVal = ??? // error
 infix var toplevelVar = ??? // error
 infix def toplevelDef = ??? // error