[CodeCompletion] Let FindLocalVal walk into ExprPattern

Some conditions in control flow statements are parsed as expression
patterns, then resolved to "pattern"s later in Sema. In code completion,
they might not be type checked at all. Previously, when collecting
visible declarations for completion candidates, it didn't walk into
`ExprPattern`, and thus it didn't find the variables inside. Use
standard `Pattern::forEachVariable()` that looks into `ExprPattern`
instead of using its custom recursive logic.

rdar://86050684

Author: rintaro

lib/AST/NameLookup.cpp

@@ -2778,40 +2778,7 @@ swift::getDirectlyInheritedNominalTypeDecls(
 }
 
 void FindLocalVal::checkPattern(const Pattern *Pat, DeclVisibilityKind Reason) {
-  switch (Pat->getKind()) {
-  case PatternKind::Tuple:
-    for (auto &field : cast<TuplePattern>(Pat)->getElements())
-      checkPattern(field.getPattern(), Reason);
-    return;
-  case PatternKind::Paren:
-  case PatternKind::Typed:
-  case PatternKind::Binding:
-    return checkPattern(Pat->getSemanticsProvidingPattern(), Reason);
-  case PatternKind::Named:
-    return checkValueDecl(cast<NamedPattern>(Pat)->getDecl(), Reason);
-  case PatternKind::EnumElement: {
-    auto *OP = cast<EnumElementPattern>(Pat);
-    if (OP->hasSubPattern())
-      checkPattern(OP->getSubPattern(), Reason);
-    return;
-  }
-  case PatternKind::OptionalSome:
-    checkPattern(cast<OptionalSomePattern>(Pat)->getSubPattern(), Reason);
-    return;
-
-  case PatternKind::Is: {
-    auto *isPat = cast<IsPattern>(Pat);
-    if (isPat->hasSubPattern())
-      checkPattern(isPat->getSubPattern(), Reason);
-    return;
-  }
-
-  // Handle non-vars.
-  case PatternKind::Bool:
-  case PatternKind::Expr:
-  case PatternKind::Any:
-    return;
-  }
+  Pat->forEachVariable([&](VarDecl *VD) { checkValueDecl(VD, Reason); });
 }
 void FindLocalVal::checkValueDecl(ValueDecl *D, DeclVisibilityKind Reason) {
   if (!D)

test/IDE/complete_stmt_controlling_expr.swift

@@ -547,3 +547,23 @@ func testGuardCase(x:FooStruct?) {
 // OPTIONAL_FOOSTRUCT-DAG: Decl[EnumElement]/CurrNominal/IsSystem/TypeRelation[Identical]: none[#Optional<FooStruct>#]; name=none
 // OPTIONAL_FOOSTRUCT-DAG: Decl[EnumElement]/CurrNominal/IsSystem/TypeRelation[Identical]: some({#FooStruct#})[#Optional<FooStruct>#]; name=some()
 // OPTIONAL_FOOSTRUCT: End completions
+
+func returnOpt() -> String? { nil }
+func returnOptTuple() -> (String, String)? { nil}
+func test_rdar86050684() {
+  guard let local1 = returnOpt() else { return }
+  guard let (local2, _) =  returnOptTuple() else { return }
+  if let (local3, _) = returnOptTuple() {
+    if case (let local4, _)? = returnOptTuple() {
+      let (local5, _) = returnOptTuple() ?? ("", "")
+      _ = #^RDAR86050684^#
+// RDAR86050684: Begin completions
+// RDAR86050684-DAG: Decl[LocalVar]/Local:               local1[#String#];
+// RDAR86050684-DAG: Decl[LocalVar]/Local:               local2[#String#];
+// RDAR86050684-DAG: Decl[LocalVar]/Local:               local3[#String#];
+// RDAR86050684-DAG: Decl[LocalVar]/Local:               local4[#String#];
+// RDAR86050684-DAG: Decl[LocalVar]/Local:               local5[#String#];
+// RDAR86050684: End completions
+    }
+  }
+}