Fix get_column function and add some unit tests for fullwidth text

src/buffer_utils.cc

@@ -18,13 +18,15 @@ ColumnCount get_column(const Buffer& buffer,
     auto line = buffer[coord.line];
     auto col = 0_col;
     for (auto it = line.begin();
-         it != line.end() and coord.column > (int)(it - line.begin());
-         it = utf8::next(it, line.end()))
+         it != line.end() and coord.column > (int)(it - line.begin()); )
     {
         if (*it == '\t')
+        {
             col = (col / tabstop + 1) * tabstop;
+            ++it;
+        }
         else
-            ++col;
+            col += get_width(utf8::read_codepoint(it, line.end()));
     }
     return col;
 }
@@ -41,10 +43,16 @@ ByteCount get_byte_to_column(const Buffer& buffer, ColumnCount tabstop, DisplayC
             col = (col / tabstop + 1) * tabstop;
             if (col > coord.column) // the target column was in the tab
                 break;
+            ++it;
         }
         else
-            ++col;
-        it = utf8::next(it, line.end());
+        {
+            auto next = it;
+            col += get_width(utf8::read_codepoint(next, line.end()));
+            if (col > coord.column) // the target column was in the char
+                break;
+            it = next;
+        }
     }
     return (int)(it - line.begin());
 }

src/highlighters.cc

@@ -648,7 +648,7 @@ HighlighterAndId create_column_highlighter(HighlighterParameters params)
 
 void expand_tabulations(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
 {
-    const int tabstop = context.options()["tabstop"].get<int>();
+    const ColumnCount tabstop = context.options()["tabstop"].get<int>();
     auto& buffer = context.buffer();
     for (auto& line : display_buffer.lines())
     {
@@ -668,8 +668,8 @@ void expand_tabulations(const Context& context, HighlightFlags flags, DisplayBuf
                     if (it+1 != end)
                         atom_it = line.split(atom_it, (it+1).coord());
 
-                    int column = (int)get_column(buffer, tabstop, it.coord());
-                    int count = tabstop - (column % tabstop);
+                    ColumnCount column = get_column(buffer, tabstop, it.coord());
+                    ColumnCount count = tabstop - (column % tabstop);
                     String padding;
                     for (int i = 0; i < count; ++i)
                         padding += ' ';

test/unit/codepoint-width/tab-width/cmd

@@ -0,0 +1 @@
+j

test/unit/codepoint-width/tab-width/in

@@ -0,0 +1,2 @@
+一	%(二)
+1234567890

test/unit/codepoint-width/tab-width/selections

@@ -0,0 +1 @@
+9

test/unit/codepoint-width/vertical-movement/cmd

@@ -0,0 +1 @@
+k

test/unit/codepoint-width/vertical-movement/in

@@ -0,0 +1,2 @@
+123456789012
+一%(二)三%(四)五六

test/unit/codepoint-width/vertical-movement/selections

@@ -0,0 +1 @@
+3:7