fix(core/rust): more careful management of ShortString capacity

core/embed/rust/src/ui/component/text/common.rs

@@ -2,7 +2,6 @@ use crate::{
     strutil::ShortString,
     ui::{component::EventCtx, util::ResultExt},
 };
-use heapless::String;
 
 /// Reified editing operations of `TextBox`.
 ///
@@ -22,14 +21,15 @@ pub struct TextBox {
 
 impl TextBox {
     /// Create a new `TextBox` with content `text`.
-    pub fn new(text: &str) -> Self {
+    pub fn new(text: &str, max_len: usize) -> Self {
-        let text = unwrap!(String::try_from(text));
+        let text = unwrap!(ShortString::try_from(text));
+        debug_assert!(text.capacity() >= max_len);
         Self { text }
     }
 
     /// Create an empty `TextBox`.
-    pub fn empty() -> Self {
+    pub fn empty(max_len: usize) -> Self {
-        Self::new("")
+        Self::new("", max_len)
     }
 
     pub fn content(&self) -> &str {

core/embed/rust/src/ui/model_mercury/component/keyboard/bip39.rs

@@ -176,7 +176,7 @@ impl Bip39Input {
     pub fn new() -> Self {
         Self {
             button: Button::empty(),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             options_num: None,
             suggested_word: None,
@@ -193,7 +193,7 @@ impl Bip39Input {
         // Styling the input to reflect already filled word
         Self {
             button: Button::empty().styled(theme::button_recovery_confirm()),
-            textbox: TextBox::new(word),
+            textbox: TextBox::new(word, MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             options_num: bip39::options_num(word),
             suggested_word: bip39::complete_word(word),

core/embed/rust/src/ui/model_mercury/component/keyboard/passphrase.rs

@@ -414,7 +414,7 @@ impl Input {
     fn new() -> Self {
         Self {
             area: Rect::zero(),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
         }
     }

core/embed/rust/src/ui/model_mercury/component/keyboard/pin.rs

@@ -1,5 +1,4 @@
 use core::mem;
-use heapless::String;
 
 use crate::{
     strutil::{ShortString, TString},
@@ -294,7 +293,7 @@ impl PinDots {
             area: Rect::zero(),
             pad: Pad::with_background(style.background_color),
             style,
-            digits: String::new(),
+            digits: ShortString::new(),
             display_digits: false,
         }
     }

core/embed/rust/src/ui/model_mercury/component/keyboard/slip39.rs

@@ -1,7 +1,5 @@
 use core::iter;
 
-use heapless::String;
-
 use crate::{
     strutil::ShortString,
     trezorhal::slip39,
@@ -204,7 +202,7 @@ impl Slip39Input {
         Self {
             // Button has the same style the whole time
             button: Button::empty().styled(theme::button_recovery_confirm()),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             final_word: None,
             input_mask: Slip39Mask::full(),
@@ -222,7 +220,7 @@ impl Slip39Input {
         Self {
             // Button has the same style the whole time
             button: Button::empty().styled(theme::button_recovery_confirm()),
-            textbox: TextBox::new(&buff),
+            textbox: TextBox::new(&buff, MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             final_word,
             input_mask,

core/embed/rust/src/ui/model_tr/component/input_methods/passphrase.rs

@@ -11,8 +11,6 @@ use crate::{
     },
 };
 
-use heapless::String;
-
 use super::super::{
     theme, ButtonDetails, ButtonLayout, CancelConfirmMsg, ChangingTextLine, ChoiceFactory,
     ChoiceItem, ChoicePage,
@@ -286,19 +284,24 @@ impl PassphraseEntry {
             passphrase_dots: Child::new(ChangingTextLine::center_mono("", MAX_PASSPHRASE_LENGTH)),
             show_plain_passphrase: false,
             show_last_digit: false,
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_PASSPHRASE_LENGTH),
             current_category: ChoiceCategory::Menu,
         }
     }
 
     fn update_passphrase_dots(&mut self, ctx: &mut EventCtx) {
+        debug_assert!({
+            let s = ShortString::new();
+            s.capacity() >= MAX_PASSPHRASE_LENGTH
+        });
+
         let text_to_show = if self.show_plain_passphrase {
-            unwrap!(String::try_from(self.passphrase()))
+            unwrap!(ShortString::try_from(self.passphrase()))
         } else if self.is_empty() {
-            unwrap!(String::try_from(""))
+            unwrap!(ShortString::try_from(""))
         } else {
             // Showing asterisks and possibly the last digit.
-            let mut dots: ShortString = String::new();
+            let mut dots = ShortString::new();
             for _ in 0..self.textbox.len() - 1 {
                 unwrap!(dots.push('*'));
             }

core/embed/rust/src/ui/model_tr/component/input_methods/pin.rs

@@ -14,7 +14,6 @@ use super::super::{
     theme, ButtonDetails, ButtonLayout, CancelConfirmMsg, ChangingTextLine, ChoiceFactory,
     ChoiceItem, ChoicePage,
 };
-use heapless::String;
 
 #[derive(Clone, Copy)]
 enum PinAction {
@@ -179,7 +178,7 @@ impl<'a> PinEntry<'a> {
             showing_real_prompt,
             show_real_pin: false,
             show_last_digit: false,
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_PIN_LENGTH),
         }
     }
 
@@ -192,15 +191,19 @@ impl<'a> PinEntry<'a> {
     /// Show updated content in the changing line.
     /// Many possibilities, according to the PIN state.
     fn update_pin_line(&mut self, ctx: &mut EventCtx) {
+        debug_assert!({
+            let s = ShortString::new();
+            s.capacity() >= MAX_PIN_LENGTH
+        });
         let mut used_font = Font::BOLD;
         let pin_line_text = if self.is_empty() && !self.subprompt.is_empty() {
             // Showing the subprompt in NORMAL font
             used_font = Font::NORMAL;
-            self.subprompt.map(|s| unwrap!(String::try_from(s)))
+            self.subprompt.map(|s| unwrap!(ShortString::try_from(s)))
         } else if self.is_empty() {
-            unwrap!(String::try_from(EMPTY_PIN_STR))
+            unwrap!(ShortString::try_from(EMPTY_PIN_STR))
         } else if self.show_real_pin {
-            unwrap!(String::try_from(self.pin()))
+            unwrap!(ShortString::try_from(self.pin()))
         } else {
             // Showing asterisks and possibly the last digit.
             let mut dots = ShortString::new();

core/embed/rust/src/ui/model_tr/component/input_methods/wordlist.rs

@@ -10,7 +10,7 @@ use crate::{
 };
 
 use super::super::{theme, ButtonLayout, ChangingTextLine, ChoiceFactory, ChoiceItem, ChoicePage};
-use heapless::{String, Vec};
+use heapless::Vec;
 
 enum WordlistAction {
     Letter(char),
@@ -176,7 +176,7 @@ impl WordlistEntry {
                 .with_carousel(true)
                 .with_initial_page_counter(get_random_position(choices_count)),
             chosen_letters: Child::new(ChangingTextLine::center_mono(PROMPT, LINE_CAPACITY)),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_WORD_LENGTH),
             offer_words: false,
             wordlist_type,
             can_go_back,
@@ -196,7 +196,7 @@ impl WordlistEntry {
                 .with_incomplete(true)
                 .with_initial_page_counter(1),
             chosen_letters: Child::new(ChangingTextLine::center_mono(word, LINE_CAPACITY)),
-            textbox: TextBox::new(word),
+            textbox: TextBox::new(word, MAX_WORD_LENGTH),
             offer_words: false,
             wordlist_type,
             can_go_back,

core/embed/rust/src/ui/model_tt/component/keyboard/bip39.rs

@@ -210,7 +210,7 @@ impl Bip39Input {
     pub fn new() -> Self {
         Self {
             button: Button::empty(),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             options_num: None,
             suggested_word: None,
@@ -227,7 +227,7 @@ impl Bip39Input {
         // Styling the input to reflect already filled word
         Self {
             button: Button::with_icon(theme::ICON_LIST_CHECK).styled(theme::button_pin_confirm()),
-            textbox: TextBox::new(word),
+            textbox: TextBox::new(word, MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             options_num: bip39::options_num(word),
             suggested_word: bip39::complete_word(word),

core/embed/rust/src/ui/model_tt/component/keyboard/passphrase.rs

@@ -337,7 +337,7 @@ impl Input {
     fn new() -> Self {
         Self {
             area: Rect::zero(),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
         }
     }

core/embed/rust/src/ui/model_tt/component/keyboard/pin.rs

@@ -1,5 +1,4 @@
-use core::{char::MAX, mem};
+use core::mem;
-use heapless::String;
 
 use crate::{
     strutil::{ShortString, TString},
@@ -316,11 +315,13 @@ impl PinDots {
     const TWITCH: i16 = 4;
 
     fn new(style: TextStyle) -> Self {
+        let digits = ShortString::new();
+        debug_assert!(digits.capacity() >= MAX_LENGTH);
         Self {
             area: Rect::zero(),
             pad: Pad::with_background(style.background_color),
             style,
-            digits: String::new(),
+            digits,
             display_digits: false,
         }
     }

core/embed/rust/src/ui/model_tt/component/keyboard/slip39.rs

@@ -1,7 +1,5 @@
 use core::iter;
 
-use heapless::String;
-
 use crate::{
     strutil::ShortString,
     trezorhal::slip39,
@@ -263,7 +261,7 @@ impl Slip39Input {
         Self {
             // Button has the same style the whole time
             button: Button::empty().styled(theme::button_pin_confirm()),
-            textbox: TextBox::empty(),
+            textbox: TextBox::empty(MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             final_word: None,
             input_mask: Slip39Mask::full(),
@@ -281,7 +279,7 @@ impl Slip39Input {
         Self {
             // Button has the same style the whole time
             button: Button::empty().styled(theme::button_pin_confirm()),
-            textbox: TextBox::new(&buff),
+            textbox: TextBox::new(&buff, MAX_LENGTH),
             multi_tap: MultiTapKeyboard::new(),
             final_word,
             input_mask,
@@ -290,6 +288,7 @@ impl Slip39Input {
 
     fn setup_from_prefilled_word(word: &str) -> (ShortString, Slip39Mask, Option<&'static str>) {
         let mut buff = ShortString::new();
+        debug_assert!(buff.capacity() >= MAX_LENGTH);
 
         // Gradually appending encoded key digits to the buffer and checking if
         // have not already formed a final word.

core/embed/rust/src/ui/util.rs

@@ -9,8 +9,6 @@ use crate::{
     },
 };
 
-use heapless::String;
-
 use super::display::Font;
 
 pub trait ResultExt {
@@ -129,7 +127,7 @@ pub fn icon_text_center(
 
 /// Convert char to a ShortString.
 pub fn char_to_string(ch: char) -> ShortString {
-    let mut s = String::new();
+    let mut s = ShortString::new();
     unwrap!(s.push(ch));
     s
 }
@@ -137,8 +135,7 @@ pub fn char_to_string(ch: char) -> ShortString {
 /// Returns text to be fit on one line of a given length.
 /// When the text is too long to fit, it is truncated with ellipsis
 /// on the left side.
-/// Hardcoding 50 (via ShortString) as the length of the returned String -
+/// This assumes no lines are longer than 50 chars (ShortString limit)
-/// there should not be any lines as long as this.
 pub fn long_line_content_with_ellipsis(
     text: &str,
     ellipsis: &str,
@@ -146,7 +143,7 @@ pub fn long_line_content_with_ellipsis(
     available_width: i16,
 ) -> ShortString {
     if text_font.text_width(text) <= available_width {
-        unwrap!(String::try_from(text)) // whole text can fit
+        unwrap!(ShortString::try_from(text)) // whole text can fit
     } else {
         // Text is longer, showing its right end with ellipsis at the beginning.
         // Finding out how many additional text characters will fit in,