Everywhere: Prevent risky implicit casts of (Nonnull)RefPtr

Our existing implementation did not check the element type of the other
pointer in the constructors and move assignment operators. This meant
that some operations that would require explicit casting on raw pointers
were done implicitly, such as:
- downcasting a base class to a derived class (e.g. `Kernel::Inode` =>
  `Kernel::ProcFSDirectoryInode` in Kernel/ProcFS.cpp),
- casting to an unrelated type (e.g. `Promise<bool>` => `Promise<Empty>`
  in LibIMAP/Client.cpp)

This, of course, allows gross violations of the type system, and makes
the need to type-check less obvious before downcasting. Luckily, while
adding the `static_ptr_cast`s, only two truly incorrect usages were
found; in the other instances, our casts just needed to be made
explicit.

Userland/Libraries/LibGL/Tex/TextureUnit.cpp

@@ -13,7 +13,7 @@ void TextureUnit::bind_texture_to_target(GLenum texture_target, const RefPtr<Tex
 {
     switch (texture_target) {
     case GL_TEXTURE_2D:
-        m_texture_target_2d = texture;
+        m_texture_target_2d = static_ptr_cast<Texture2D>(texture);
         m_currently_bound_texture = texture;
         m_currently_bound_target = GL_TEXTURE_2D;
         break;

Userland/Libraries/LibIMAP/Client.cpp

@@ -31,7 +31,7 @@ RefPtr<Promise<Empty>> Client::connect()
     }
     if (!success)
         return {};
-    m_connect_pending = Promise<bool>::construct();
+    m_connect_pending = Promise<Empty>::construct();
     return m_connect_pending;
 }
 

Userland/Libraries/LibIMAP/Client.h

@@ -69,7 +69,7 @@ private:
     // Not yet sent
     Vector<Command> m_command_queue {};
 
-    RefPtr<Promise<bool>> m_connect_pending {};
+    RefPtr<Promise<Empty>> m_connect_pending {};
 
     ByteBuffer m_buffer;
     Parser m_parser;

Userland/Libraries/LibJS/Parser.cpp

@@ -1606,7 +1606,7 @@ NonnullRefPtr<Identifier> Parser::parse_identifier()
         token.value());
 }
 
-NonnullRefPtr<CallExpression> Parser::parse_call_expression(NonnullRefPtr<Expression> lhs)
+NonnullRefPtr<Expression> Parser::parse_call_expression(NonnullRefPtr<Expression> lhs)
 {
     auto rule_start = push_start();
     if (!m_state.allow_super_constructor_call && is<SuperExpression>(*lhs))

Userland/Libraries/LibJS/Parser.h

@@ -85,7 +85,7 @@ public:
     NonnullRefPtr<StringLiteral> parse_string_literal(const Token& token, bool in_template_literal = false);
     NonnullRefPtr<TemplateLiteral> parse_template_literal(bool is_tagged);
     NonnullRefPtr<Expression> parse_secondary_expression(NonnullRefPtr<Expression>, int min_precedence, Associativity associate = Associativity::Right);
-    NonnullRefPtr<CallExpression> parse_call_expression(NonnullRefPtr<Expression>);
+    NonnullRefPtr<Expression> parse_call_expression(NonnullRefPtr<Expression>);
     NonnullRefPtr<NewExpression> parse_new_expression();
     NonnullRefPtr<ClassDeclaration> parse_class_declaration();
     NonnullRefPtr<ClassExpression> parse_class_expression(bool expect_class_name);

Userland/Libraries/LibPDF/Document.cpp

@@ -146,7 +146,7 @@ Value Document::resolve(Value const& value)
     auto obj = value.as_object();
 
     if (obj->is_indirect_value())
-        return static_cast<NonnullRefPtr<IndirectValue>>(obj)->value();
+        return static_ptr_cast<IndirectValue>(obj)->value();
 
     return obj;
 }

Userland/Libraries/LibPDF/Object.h

@@ -248,7 +248,7 @@ template<IsObject To, IsObject From>
 #    undef ENUMERATE_TYPES
 #endif
 
-    return static_cast<NonnullRefPtr<To>>(obj);
+    return static_ptr_cast<To>(obj);
 }
 
 }

Userland/Libraries/LibSQL/AST/Parser.cpp

@@ -210,7 +210,7 @@ NonnullRefPtr<Insert> Parser::parse_insert_statement(RefPtr<CommonTableExpressio
                 if ((column_names.size() > 0) && (chained_expr->expressions().size() != column_names.size())) {
                     syntax_error("Number of expressions does not match number of columns");
                 } else {
-                    chained_expressions.append(chained_expression.release_nonnull());
+                    chained_expressions.append(static_ptr_cast<ChainedExpression>(chained_expression.release_nonnull()));
                 }
             } else {
                 expected("Chained expression");

Userland/Libraries/LibWeb/HTML/HTMLTableElement.cpp

@@ -72,7 +72,7 @@ NonnullRefPtr<HTMLTableCaptionElement> HTMLTableElement::create_caption()
 
     auto caption = DOM::create_element(document(), TagNames::caption, Namespace::HTML);
     pre_insert(caption, first_child());
-    return caption;
+    return static_ptr_cast<HTMLTableCaptionElement>(caption);
 }
 
 void HTMLTableElement::delete_caption()
@@ -159,7 +159,7 @@ NonnullRefPtr<HTMLTableSectionElement> HTMLTableElement::create_t_head()
 
     pre_insert(thead, child_to_append_after);
 
-    return thead;
+    return static_ptr_cast<HTMLTableSectionElement>(thead);
 }
 
 void HTMLTableElement::delete_t_head()
@@ -209,7 +209,7 @@ NonnullRefPtr<HTMLTableSectionElement> HTMLTableElement::create_t_foot()
 
     auto tfoot = DOM::create_element(document(), TagNames::tfoot, Namespace::HTML);
     append_child(tfoot);
-    return tfoot;
+    return static_ptr_cast<HTMLTableSectionElement>(tfoot);
 }
 
 void HTMLTableElement::delete_t_foot()
@@ -248,7 +248,7 @@ NonnullRefPtr<HTMLTableSectionElement> HTMLTableElement::create_t_body()
 
     pre_insert(tbody, child_to_append_after);
 
-    return tbody;
+    return static_ptr_cast<HTMLTableSectionElement>(tbody);
 }
 
 NonnullRefPtr<DOM::HTMLCollection> HTMLTableElement::rows()
@@ -287,7 +287,7 @@ DOM::ExceptionOr<NonnullRefPtr<HTMLTableRowElement>> HTMLTableElement::insert_ro
     if (index < -1 || index >= (long)rows_length) {
         return DOM::IndexSizeError::create("Index is negative or greater than the number of rows");
     }
-    auto tr = static_cast<NonnullRefPtr<HTMLTableRowElement>>(DOM::create_element(document(), TagNames::tr, Namespace::HTML));
+    auto tr = static_ptr_cast<HTMLTableRowElement>(DOM::create_element(document(), TagNames::tr, Namespace::HTML));
     if (rows_length == 0 && !has_child_of_type<HTMLTableRowElement>()) {
         auto tbody = DOM::create_element(document(), TagNames::tbody, Namespace::HTML);
         tbody->append_child(tr);

Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp

@@ -166,7 +166,7 @@ void TreeBuilder::remove_irrelevant_boxes(NodeWithStyle& root)
 {
     // The following boxes are discarded as if they were display:none:
 
-    NonnullRefPtrVector<Box> to_remove;
+    NonnullRefPtrVector<Node> to_remove;
 
     // Children of a table-column.
     for_each_in_tree_with_display<CSS::Display::TableColumn>(root, [&](Box& table_column) {