refactor: extract utf8 truncation logic to utility

Move the UTF-8 visual-width measurement and truncation helper functions
from the mpris module to a common utility
(include/util/utf8_string.hpp and src/util/utf8_string.cpp).

This decouples string truncation and width measurement
from the mpris module, allowing other modules (like mpd) to reuse.
The helper function `utf8_truncate` (formerly `truncate` in mpris)
and `utf8_width` is exported under the `waybar::util` namespace,
while the low-level `measure_and_truncate` (formerly `utf8_truncate`)
is encapsulated in an anonymous namespace in src/util/utf8_string.cpp
to avoid unnecessary API exposure.

No functional changes were made to the mpris module's behavior.

include/util/utf8_string.hpp

@@ -0,0 +1,7 @@
+#pragma once
+#include <string>
+
+namespace waybar::util {
+size_t utf8_width(const std::string& str);
+void utf8_truncate(std::string& s, const std::string& ellipsis, size_t max_len);
+}  // namespace waybar::util

meson.build

@@ -186,7 +186,8 @@ src_files = files(
     'src/util/icon_loader.cpp',
     'src/util/regex_collection.cpp',
     'src/util/css_reload_helper.cpp',
-    'src/util/transform_8bit_to_rgba.cpp'
+    'src/util/transform_8bit_to_rgba.cpp',
+    'src/util/utf8_string.cpp'
 )
 
 man_files = files(

src/modules/mpris/mpris.cpp

@@ -7,6 +7,7 @@
 #include <string>
 
 #include "util/scope_guard.hpp"
+#include "util/utf8_string.hpp"
 
 extern "C" {
 #include <playerctl/playerctl.h>
@@ -202,69 +203,22 @@ auto Mpris::getIconFromJson(const Json::Value& icons, const std::string& key) ->
 // Wide characters count as two, zero-width characters count as zero
 // Modifies str in-place (unless width = std::string::npos)
 // Returns the total width of the string pre-truncating
-size_t utf8_truncate(std::string& str, size_t width = std::string::npos) {
-  if (str.length() == 0) return 0;
-
-  const gchar* trunc_end = nullptr;
-
-  size_t total_width = 0;
-
-  for (gchar *data = str.data(), *end = data + str.size(); data != nullptr;) {
-    gunichar c = g_utf8_get_char_validated(data, end - data);
-    if (c == -1U || c == -2U) {
-      // invalid unicode, treat string as ascii
-      if (width != std::string::npos && str.length() > width) str.resize(width);
-      return str.length();
-    } else if (g_unichar_iswide(c)) {
-      total_width += 2;
-    } else if (!g_unichar_iszerowidth(c) && c != 0xAD) {  // neither zero-width nor soft hyphen
-      total_width += 1;
-    }
-
-    data = g_utf8_find_next_char(data, end);
-    if (width != std::string::npos && total_width <= width && !g_unichar_isspace(c))
-      trunc_end = data;
-  }
-
-  if (trunc_end) str.resize(trunc_end - str.data());
-
-  return total_width;
-}
-
-size_t utf8_width(const std::string& str) { return utf8_truncate(const_cast<std::string&>(str)); }
-
-void truncate(std::string& s, const std::string& ellipsis, size_t max_len) {
-  if (max_len == 0) {
-    s.resize(0);
-    return;
-  }
-  size_t len = utf8_truncate(s, max_len);
-  if (len > max_len) {
-    size_t ellipsis_len = utf8_width(ellipsis);
-    if (max_len >= ellipsis_len) {
-      if (ellipsis_len) utf8_truncate(s, max_len - ellipsis_len);
-      s += ellipsis;
-    } else {
-      s.resize(0);
-    }
-  }
-}
 
 auto Mpris::getArtistStr(const PlayerInfo& info, bool truncated) -> std::string {
   auto artist = info.artist.value_or(std::string());
-  if (truncated && artist_len_ >= 0) truncate(artist, ellipsis_, artist_len_);
+  if (truncated && artist_len_ >= 0) waybar::util::utf8_truncate(artist, ellipsis_, artist_len_);
   return artist;
 }
 
 auto Mpris::getAlbumStr(const PlayerInfo& info, bool truncated) -> std::string {
   auto album = info.album.value_or(std::string());
-  if (truncated && album_len_ >= 0) truncate(album, ellipsis_, album_len_);
+  if (truncated && album_len_ >= 0) waybar::util::utf8_truncate(album, ellipsis_, album_len_);
   return album;
 }
 
 auto Mpris::getTitleStr(const PlayerInfo& info, bool truncated) -> std::string {
   auto title = info.title.value_or(std::string());
-  if (truncated && title_len_ >= 0) truncate(title, ellipsis_, title_len_);
+  if (truncated && title_len_ >= 0) waybar::util::utf8_truncate(title, ellipsis_, title_len_);
   return title;
 }
 
@@ -292,9 +246,9 @@ auto Mpris::getDynamicStr(const PlayerInfo& info, bool truncated, bool html) ->
   // keep position format same as length format
   auto position = getPositionStr(info, truncated && truncate_hours_ && length.length() < 6);
 
-  size_t artistLen = utf8_width(artist);
-  size_t albumLen = utf8_width(album);
-  size_t titleLen = utf8_width(title);
+  size_t artistLen = waybar::util::utf8_width(artist);
+  size_t albumLen = waybar::util::utf8_width(album);
+  size_t titleLen = waybar::util::utf8_width(title);
   size_t lengthLen = length.length();
   size_t posLen = position.length();
 
@@ -313,7 +267,7 @@ auto Mpris::getDynamicStr(const PlayerInfo& info, bool truncated, bool html) ->
     // Since the first element doesn't present a separator and we don't know a priori which one
     // it will be, we add a "virtual separatorLen" to the dynamicLen, since we are adding the
     // separatorLen to all the other lengths.
-    size_t separatorLen = utf8_width(dynamic_separator_);
+    size_t separatorLen = waybar::util::utf8_width(dynamic_separator_);
     size_t dynamicLen = dynamic_len_ + separatorLen;
     if (showArtist) artistLen += separatorLen;
     if (showAlbum) albumLen += separatorLen;

src/util/utf8_string.cpp

@@ -0,0 +1,62 @@
+#include <glib.h>
+
+#include <string>
+#include <util/utf8_string.hpp>
+
+namespace waybar::util {
+
+namespace {
+// Wide characters count as two, zero-width characters count as zero
+// Modifies str in-place (unless width = std::string::npos)
+// Returns the total width of the string pre-truncating
+size_t measure_and_truncate(std::string& str, size_t width = std::string::npos) {
+  if (str.length() == 0) return 0;
+
+  const gchar* trunc_end = nullptr;
+
+  size_t total_width = 0;
+
+  for (gchar *data = str.data(), *end = data + str.size(); data != nullptr;) {
+    gunichar c = g_utf8_get_char_validated(data, end - data);
+    if (c == -1U || c == -2U) {
+      // invalid unicode, treat string as ascii
+      if (width != std::string::npos && str.length() > width) str.resize(width);
+      return str.length();
+    } else if (g_unichar_iswide(c)) {
+      total_width += 2;
+    } else if (!g_unichar_iszerowidth(c) && c != 0xAD) {  // neither zero-width nor soft hyphen
+      total_width += 1;
+    }
+
+    data = g_utf8_find_next_char(data, end);
+    if (width != std::string::npos && total_width <= width && !g_unichar_isspace(c))
+      trunc_end = data;
+  }
+
+  if (trunc_end) str.resize(trunc_end - str.data());
+
+  return total_width;
+}
+}  // namespace
+
+size_t utf8_width(const std::string& str) {
+  return measure_and_truncate(const_cast<std::string&>(str));
+}
+
+void utf8_truncate(std::string& s, const std::string& ellipsis, size_t max_len) {
+  if (max_len == 0) {
+    s.resize(0);
+    return;
+  }
+  size_t len = measure_and_truncate(s, max_len);
+  if (len > max_len) {
+    size_t ellipsis_len = utf8_width(ellipsis);
+    if (max_len >= ellipsis_len) {
+      if (ellipsis_len) measure_and_truncate(s, max_len - ellipsis_len);
+      s += ellipsis;
+    } else {
+      s.resize(0);
+    }
+  }
+}
+}  // namespace waybar::util