Fix inferring effectful while header (#902)

Should fix #601

Author: PhictionalOne

effekt/shared/src/main/scala/effekt/Typer.scala

@@ -119,7 +119,7 @@ object Typer extends Phase[NameResolved, Typechecked] {
           checkStmt(s, expectedType)
         }.getOrElse(Result(TUnit, ConcreteEffects.empty))
 
-        Result(Context.join(bodyTpe, defaultTpe), defaultEffs ++ bodyEffs)
+        Result(Context.join(bodyTpe, defaultTpe), defaultEffs ++ bodyEffs ++ guardEffs)
 
       case source.Var(id) => id.symbol match {
         case x: RefBinder => Context.lookup(x) match {

examples/neg/typer/infer-effectful-while.check

@@ -0,0 +1,3 @@
+[error] examples/neg/typer/infer-effectful-while.effekt:14:1: Main cannot have effects, but includes effects: { Foo }
+def main() = {
+^

examples/neg/typer/infer-effectful-while.effekt

@@ -0,0 +1,16 @@
+interface Foo { def foo(): Unit }
+
+def bar(): Bool / Foo = {
+  do foo()
+  false
+}
+
+def fooo() = {
+  while(bar() is true) {
+      ()
+    }
+}
+
+def main() = {
+  fooo()
+}