Allow attaching length limit to InputField.

ui/widgets/fields/input_field.cpp

@@ -6,8 +6,9 @@
 //
 #include "ui/widgets/fields/input_field.h"
 
-#include "ui/widgets/popup_menu.h"
 #include "ui/text/text.h"
+#include "ui/widgets/labels.h"
+#include "ui/widgets/popup_menu.h"
 #include "ui/emoji_config.h"
 #include "ui/ui_utility.h"
 #include "ui/painter.h"
@@ -134,7 +135,7 @@ bool IsNewline(QChar ch) {
 }
 
 [[nodiscard]] bool IsCustomEmojiLink(QStringView link) {
-	return link.startsWith(Ui::InputField::kCustomEmojiTagStart);
+	return link.startsWith(InputField::kCustomEmojiTagStart);
 }
 
 [[nodiscard]] QString MakeUniqueCustomEmojiLink(QStringView link) {
@@ -153,7 +154,7 @@ bool IsNewline(QChar ch) {
 }
 
 [[nodiscard]] uint64 CustomEmojiIdFromLink(QStringView link) {
-	const auto skip = Ui::InputField::kCustomEmojiTagStart.size();
+	const auto skip = InputField::kCustomEmojiTagStart.size();
 	const auto index = link.indexOf('?', skip + 1);
 	return base::StringViewMid(
 		link,
@@ -1131,7 +1132,7 @@ QSizeF CustomEmojiObject::intrinsicSize(
 	const auto width = size + st::emojiPadding * 2.;
 	const auto height = std::max(_font->height * 1., size);
 	if (!_skip) {
-		const auto emoji = Ui::Text::AdjustCustomEmojiSize(st::emojiSize);
+		const auto emoji = Text::AdjustCustomEmojiSize(st::emojiSize);
 		_skip = (st::emojiSize - emoji) / 2;
 	}
 	return { width, height };
@@ -3190,7 +3191,7 @@ void InputField::inputMethodEventInner(QInputMethodEvent *e) {
 	}
 	_inputMethodCommit = e->commitString();
 
-	const auto weak = Ui::MakeWeak(this);
+	const auto weak = MakeWeak(this);
 	_inner->QTextEdit::inputMethodEvent(e);
 
 	if (weak && _inputMethodCommit.has_value()) {
@@ -4066,4 +4067,52 @@ int FieldCharacterCount(not_null<InputField*> field) {
 	return field->lastTextSizeWithoutSurrogatePairsCount();
 }
 
+void AddLengthLimitLabel(not_null<InputField*> field, int limit) {
+	struct State {
+		rpl::variable<int> length;
+	};
+	const auto state = field->lifetime().make_state<State>();
+	state->length = rpl::single(
+		rpl::empty
+	) | rpl::then(field->changes()) | rpl::map([=] {
+		return int(field->getLastText().size());
+	});
+	const auto allowExceed = std::max(limit / 2, 9);
+	field->setMaxLength(limit + allowExceed);
+	const auto threshold = std::min(limit / 2, 9);
+	auto warningText = state->length.value() | rpl::map([=](int count) {
+		const auto left = limit - count;
+		return (left < threshold) ? QString::number(left) : QString();
+	});
+	const auto warning = CreateChild<FlatLabel>(
+		field.get(),
+		std::move(warningText),
+		st::defaultInputFieldLimit);
+
+	const auto maxSize = st::defaultInputFieldLimit.style.font->width(
+		QString::number(-allowExceed));
+	const auto add = std::max(maxSize - field->st().textMargins.right(), 0);
+	if (add) {
+		field->setAdditionalMargins({ 0, 0, add, 0 });
+	}
+	state->length.value() | rpl::map(
+		rpl::mappers::_1 > limit
+	) | rpl::start_with_next([=](bool exceeded) {
+		warning->setTextColorOverride(exceeded
+			? st::attentionButtonFg->c
+			: std::optional<QColor>());
+	}, warning->lifetime());
+	rpl::combine(
+		field->sizeValue(),
+		warning->sizeValue()
+	) | rpl::start_with_next([=] {
+		// Baseline alignment.
+		const auto top = field->st().textMargins.top()
+			+ field->st().font->ascent
+			- st::defaultInputFieldLimit.style.font->ascent;
+		warning->moveToRight(0, top);
+	}, warning->lifetime());
+	warning->setAttribute(Qt::WA_TransparentForMouseEvents);
+}
+
 } // namespace Ui

ui/widgets/fields/input_field.h

@@ -586,4 +586,6 @@ void PrepareFormattingOptimization(not_null<QTextDocument*> document);
 
 [[nodiscard]] int FieldCharacterCount(not_null<InputField*> field);
 
+void AddLengthLimitLabel(not_null<InputField*> field, int limit);
+
 } // namespace Ui

ui/widgets/widgets.style

@@ -910,6 +910,9 @@ defaultInputField: InputField {
 	heightMin: 55px;
 	heightMax: 148px;
 }
+defaultInputFieldLimit: FlatLabel(defaultFlatLabel) {
+	textFg: windowSubTextFg;
+}
 
 defaultIconButton: IconButton {
 	iconPosition: point(-1px, -1px);