Remove leading infix test for if condition

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1830,14 +1830,14 @@ object Parsers {
      *  the initially parsed (...) region?
      */
     def toBeContinued(altToken: Token): Boolean =
-      if in.isNewLine || migrateTo3 then
-        false // a newline token means the expression is finished
-      else if !in.canStartStatTokens.contains(in.token)
-              || in.isLeadingInfixOperator(inConditional = true)
-      then
-        true
-      else
-        followedByToken(altToken) // scan ahead to see whether we find a `then` or `do`
+      inline def canContinue =
+        !in.canStartStatTokens.contains(in.token)  // not statement, so take as continued expr
+      || followedByToken(altToken)                 // scan ahead to see whether we find a `then` or `do`
+
+      !in.isNewLine       // a newline token means the expression is finished
+      && !migrateTo3      // old syntax
+      && canContinue
+    end toBeContinued
 
     def condExpr(altToken: Token): Tree =
       val t: Tree =

tests/pos/indent.scala

@@ -82,6 +82,14 @@ object Test:
     x < 10
   do ()
 
+  def sign(x: Int): Int =
+    if (x > 0) 1
+    else if (x < 0) - 1        // was: value - is not a member of Boolean
+    else 0
+  def lessPersuasively(x: Int): Unit =
+    while (x < 0) - 42         // was: value - is not a member of Boolean
+end Test
+
 class Test2:
   self =>
   def foo(x: Int) =
@@ -147,4 +155,4 @@ class Coder(words: List[String]):
 end Coder
 
 object Test22:
-  def foo: Int = 22
+  def foo: Int = 22