vim-patch:8.2.2607: strcharpart() cannot include composing characters

Problem:    strcharpart() cannot include composing characters.
Solution:   Add the {skipcc} argument.

https://github.com/vim/vim/commit/02b4d9b18a03549b68e364e428392b7a62766c74

Co-authored-by: Bram Moolenaar <Bram@vim.org>

4 files changed, 41 insertions, 8 deletions

diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 5be9ba910b..c2dc5ddd5b 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -486,7 +486,7 @@ str2list({expr} [, {utf8}])	List	convert each character of {expr} to
 str2nr({expr} [, {base} [, {quoted}]])
 				Number	convert String to Number
 strcharlen({expr})		Number	character length of the String {expr}
-strcharpart({str}, {start} [, {len}])
+strcharpart({str}, {start} [, {len} [, {skipcc}]])
 				String	{len} characters of {str} at
 					character {start}
 strchars({expr} [, {skipcc}])	Number	character count of the String {expr}
@@ -7779,6 +7779,7 @@ slice({expr}, {start} [, {end}])			*slice()*
 		Similar to using a |slice| "expr[start : end]", but "end" is
 		used exclusive.  And for a string the indexes are used as
 		character indexes instead of byte indexes.
+		Also, composing characters are not counted.
 		When {end} is omitted the slice continues to the last item.
 		When {end} is -1 the last item is omitted.
 		Returns an empty value if {start} or {end} are invalid.
@@ -8129,12 +8130,16 @@ strcharlen({string})					*strcharlen()*
 			GetText()->strcharlen()
 
 
-strcharpart({src}, {start} [, {len}])			*strcharpart()*
+strcharpart({src}, {start} [, {len} [, {skipcc}]])		*strcharpart()*
 		Like |strpart()| but using character index and length instead
-		of byte index and length.  Composing characters are counted
-		separately.
+		of byte index and length.
+		When {skipcc} is omitted or zero, composing characters are
+		counted separately.
+		When {skipcc} set to 1, Composing characters are ignored,
+		similar to  |slice()|.
 		When a character index is used where a character does not
-		exist it is assumed to be one character.  For example: >
+		exist it is omitted and counted as one character.  For
+		example: >
 			strcharpart('abc', -1, 2)
 <		results in 'a'.
 
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index aec5191249..d9c7208c02 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -386,7 +386,7 @@ return {
     str2list={args={1, 2}, base=1},
     str2nr={args={1, 3}, base=1},
     strcharlen={args=1, base=1},
-    strcharpart={args={2, 3}, base=1, fast=true},
+    strcharpart={args={2, 4}, base=1, fast=true},
     strchars={args={1, 2}, base=1},
     strdisplaywidth={args={1, 2}, base=1},
     strftime={args={1, 2}, base=1},
diff --git a/src/nvim/strings.c b/src/nvim/strings.c
index 61e00f85dc..5231ec0841 100644
--- a/src/nvim/strings.c
+++ b/src/nvim/strings.c
@@ -1834,12 +1834,26 @@ void f_strcharpart(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   const size_t slen = strlen(p);
 
   int nbyte = 0;
+  varnumber_T skipcc = false;
   bool error = false;
   varnumber_T nchar = tv_get_number_chk(&argvars[1], &error);
   if (!error) {
+    if (argvars[2].v_type != VAR_UNKNOWN
+        && argvars[3].v_type != VAR_UNKNOWN) {
+      skipcc = tv_get_bool(&argvars[3]);
+      if (skipcc < 0 || skipcc > 1) {
+        semsg(_(e_using_number_as_bool_nr), skipcc);
+        return;
+      }
+    }
+
     if (nchar > 0) {
       while (nchar > 0 && (size_t)nbyte < slen) {
-        nbyte += utf_ptr2len(p + nbyte);
+        if (skipcc) {
+          nbyte += utfc_ptr2len(p + nbyte);
+        } else {
+          nbyte += utf_ptr2len(p + nbyte);
+        }
         nchar--;
       }
     } else {
@@ -1855,7 +1869,11 @@ void f_strcharpart(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
       if (off < 0) {
         len += 1;
       } else {
-        len += utf_ptr2len(p + off);
+        if (skipcc) {
+          len += utfc_ptr2len(p + off);
+        } else {
+          len += utf_ptr2len(p + off);
+        }
       }
       charlen--;
     }
diff --git a/test/old/testdir/test_expr_utf8.vim b/test/old/testdir/test_expr_utf8.vim
index fad725d2e5..c6d2e4ed7e 100644
--- a/test/old/testdir/test_expr_utf8.vim
+++ b/test/old/testdir/test_expr_utf8.vim
@@ -31,4 +31,14 @@ func Test_strcharpart()
   call assert_equal('a', strcharpart('àxb', 0, 1))
   call assert_equal('̀', strcharpart('àxb', 1, 1))
   call assert_equal('x', strcharpart('àxb', 2, 1))
+
+
+  call assert_equal('a', strcharpart('àxb', 0, 1, 0))
+  call assert_equal('à', strcharpart('àxb', 0, 1, 1))
+  call assert_equal('x', strcharpart('àxb', 1, 1, 1))
+
+  call assert_fails("let v = strcharpart('abc', 0, 0, [])", 'E745:')
+  call assert_fails("let v = strcharpart('abc', 0, 0, 2)", 'E1023:')
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab