try to calculate character width

maintainers/flake-module.nix

@@ -356,6 +356,7 @@
             ''^src/libutil/util\.cc$''
             ''^src/libutil/util\.hh$''
             ''^src/libutil/variant-wrapper\.hh$''
+            ''^src/libutil/widecharwidth/widechar_width\.h$'' # vendored source
             ''^src/libutil/windows/file-descriptor\.cc$''
             ''^src/libutil/windows/file-path\.cc$''
             ''^src/libutil/windows/processes\.cc$''

src/libutil-tests/terminal.cc

@@ -55,6 +55,10 @@ TEST(filterANSIEscapes, utf8)
     ASSERT_EQ(filterANSIEscapes("fóóbär", true, 3), "fóó");
     ASSERT_EQ(filterANSIEscapes("f€€bär", true, 4), "f€€b");
     ASSERT_EQ(filterANSIEscapes("f𐍈𐍈bär", true, 4), "f𐍈𐍈b");
+    ASSERT_EQ(filterANSIEscapes("f🔍bar", true, 6), "f🔍bar");
+    ASSERT_EQ(filterANSIEscapes("f🔍bar", true, 3), "f🔍");
+    ASSERT_EQ(filterANSIEscapes("f🔍bar", true, 2), "f");
+    ASSERT_EQ(filterANSIEscapes("foo\u0301", true, 3), "foó");
 }
 
 TEST(filterANSIEscapes, osc8)

src/libutil/meson.build

@@ -108,6 +108,8 @@ deps_private += cpuid
 nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
 deps_public += nlohmann_json
 
+cxx = meson.get_compiler('cpp')
+
 config_h = configure_file(
   configuration : configdata,
   output : 'config-util.hh',
@@ -168,6 +170,10 @@ sources = files(
 )
 
 include_dirs = [include_directories('.')]
+if not cxx.has_header('widechar_width.h', required : false)
+  # use vendored widechar_width.h
+  include_dirs += include_directories('./widecharwidth')
+endif
 
 headers = [config_h] + files(
   'abstract-setting-to-json.hh',

src/libutil/package.nix

@@ -29,6 +29,7 @@ mkMesonLibrary (finalAttrs: {
     ./nix-meson-build-support
     ../../.version
     ./.version
+    ./widecharwidth
     ./meson.build
     ./meson.options
     ./linux/meson.build

src/libutil/terminal.cc

@@ -11,6 +11,53 @@
 # include <sys/ioctl.h>
 #endif
 #include <unistd.h>
+#include <widechar_width.h>
+
+namespace {
+
+inline std::pair<int, size_t> charWidthUTF8Helper(std::string_view s)
+{
+    size_t bytes = 1;
+    uint32_t ch = s[0];
+    uint32_t max = 1U << 7;
+    if ((ch & 0x80U) == 0U) {
+    } else if ((ch & 0xe0U) == 0xc0U) {
+        ch &= 0x1fU;
+        bytes = 2;
+        max = 1U << 11;
+    } else if ((ch & 0xf0U) == 0xe0U) {
+        ch &= 0x0fU;
+        bytes = 3;
+        max = 1U << 16;
+    } else if ((ch & 0xf8U) == 0xf0U) {
+        ch &= 0x07U;
+        bytes = 4;
+        max = 0x110000U;
+    } else {
+        return {bytes, bytes}; // invalid UTF-8 start byte
+    }
+    for (size_t i = 1; i < bytes; i++) {
+        if (i < s.size() && (s[i] & 0xc0) == 0x80) {
+            ch = (ch << 6) | (s[i] & 0x3f);
+        } else {
+            return {i, i}; // invalid UTF-8 encoding; assume one character per byte
+        }
+    }
+    int width = bytes; // in case of overlong encoding
+    if (ch < max) {
+        width = widechar_wcwidth(ch);
+        if (width == widechar_ambiguous) {
+            width = 1; // just a guess...
+        } else if (width == widechar_widened_in_9) {
+            width = 2;
+        } else if (width < 0) {
+            width = 0;
+        }
+    }
+    return {width, bytes};
+}
+
+}
 
 namespace nix {
 
@@ -30,7 +77,7 @@ std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int w
     size_t w = 0;
     auto i = s.begin();
 
-    while (w < (size_t) width && i != s.end()) {
+    while (i != s.end()) {
 
         if (*i == '\e') {
             std::string e;
@@ -61,10 +108,12 @@ std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int w
         }
 
         else if (*i == '\t') {
-            i++; t += ' '; w++;
+            do {
-            while (w < (size_t) width && w % 8) {
+                if (++w > (size_t) width)
-                t += ' '; w++;
+                    return t;
-            }
+                t += ' ';
+            } while (w % 8);
+            i++;
         }
 
         else if (*i == '\r' || *i == '\a')
@@ -72,35 +121,18 @@ std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int w
             i++;
 
         else {
-            w++;
+            auto [chWidth, bytes] = charWidthUTF8Helper({i, s.end()});
-            // Copy one UTF-8 character.
+            w += chWidth;
-            if ((*i & 0xe0) == 0xc0) {
+            if (w > (size_t) width) {
-                t += *i++;
+                break;
-                if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
+            }
-            } else if ((*i & 0xf0) == 0xe0) {
+            t += {i, i + bytes};
-                t += *i++;
+            i += bytes;
-                if (i != s.end() && ((*i & 0xc0) == 0x80)) {
-                    t += *i++;
-                    if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
-                }
-            } else if ((*i & 0xf8) == 0xf0) {
-                t += *i++;
-                if (i != s.end() && ((*i & 0xc0) == 0x80)) {
-                    t += *i++;
-                    if (i != s.end() && ((*i & 0xc0) == 0x80)) {
-                        t += *i++;
-                        if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
-                    }
-                }
-            } else
-                t += *i++;
         }
     }
-
     return t;
 }
 
-
 //////////////////////////////////////////////////////////////////////
 
 static Sync<std::pair<unsigned short, unsigned short>> windowSize{{0, 0}};

src/libutil/widecharwidth/LICENSE

@@ -0,0 +1,4 @@
+widecharwidth - wcwidth implementation
+Written in 2018 by ridiculous_fish
+To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to this software to the public domain worldwide. This software is distributed without any warranty.
+You should have received a copy of the CC0 Public Domain Dedication along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.