[Sema] Fix spurious trailing closure warning

With the argument list refactoring, it's no
longer sufficient to stop walking when we encounter
an explicit tuple or paren. Add an additional
check to stop walking when we encounter an explicit
argument list.

rdar://85343171

Author: hamishknight

lib/Sema/MiscDiagnostics.cpp

@@ -3509,6 +3509,13 @@ static void checkStmtConditionTrailingClosure(ASTContext &ctx, const Expr *E) {
 
     bool shouldWalkIntoTapExpression() override { return false; }
 
+    std::pair<bool, ArgumentList *>
+    walkToArgumentListPre(ArgumentList *args) override {
+      // Don't walk into an explicit argument list, as trailing closures that
+      // appear in child arguments are fine.
+      return {args->isImplicit(), args};
+    }
+
     std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
       switch (E->getKind()) {
       case ExprKind::Paren:

test/expr/closure/trailing.swift

@@ -466,3 +466,12 @@ class TrailingDerived : TrailingBase {
     super.init(x: x) {}
   }
 }
+
+// rdar://85343171 - Spurious warning on trailing closure in argument list.
+func rdar85343171() {
+  func foo(_ i: Int) -> Bool { true }
+  func bar(_ fn: () -> Void) -> Int { 0 }
+
+  // Okay, as trailing closure is nested in argument list.
+  if foo(bar {}) {}
+}