patch 9.0.0916: getbufline() is inefficient for getting a single line

Problem:    getbufline() is inefficient for getting a single line.
Solution:   Add getbufoneline().

runtime/doc/builtin.txt

@@ -208,6 +208,7 @@ get({func}, {what})		any	get property of funcref/partial {func}
 getbufinfo([{buf}])		List	information about buffers
 getbufline({buf}, {lnum} [, {end}])
 				List	lines {lnum} to {end} of buffer {buf}
+getbufoneline({buf}, {lnum})	String	line {lnum} of buffer {buf}
 getbufvar({buf}, {varname} [, {def}])
 				any	variable {varname} in buffer {buf}
 getchangelist([{buf}])		List	list of change list items
@@ -3204,7 +3205,8 @@ getbufinfo([{dict}])
 getbufline({buf}, {lnum} [, {end}])
 		Return a |List| with the lines starting from {lnum} to {end}
 		(inclusive) in the buffer {buf}.  If {end} is omitted, a
-		|List| with only the line {lnum} is returned.
+		|List| with only the line {lnum} is returned.  See
+		`getbufoneline()` for only getting the line.
 
 		For the use of {buf}, see |bufname()| above.
 
@@ -3227,6 +3229,11 @@ getbufline({buf}, {lnum} [, {end}])
 
 <		Can also be used as a |method|: >
 			GetBufnr()->getbufline(lnum)
+<
+							*getbufoneline()*
+getbufoneline({buf}, {lnum})
+		Just like `getbufline()` but only get one line and return it
+		as a string.
 
 getbufvar({buf}, {varname} [, {def}])				*getbufvar()*
 		The result is the value of option or local buffer variable
@@ -3771,7 +3778,8 @@ getline({lnum} [, {end}])
 <		Can also be used as a |method|: >
 			ComputeLnum()->getline()
 
-<		To get lines from another buffer see |getbufline()|
+<		To get lines from another buffer see |getbufline()| and
+		|getbufoneline()|
 
 getloclist({nr} [, {what}])				*getloclist()*
 		Returns a |List| with all the entries in the location list for

runtime/doc/usr_41.txt

@@ -935,6 +935,7 @@ Working with text in the current buffer:		*text-functions*
 
 Working with text in another buffer:
 	getbufline()		get a list of lines from the specified buffer
+	getbufoneline()		get a one line from the specified buffer
 	setbufline()		replace a line in the specified buffer
 	appendbufline()		append a list of lines in the specified buffer
 	deletebufline()		delete lines from a specified buffer

src/evalbuffer.c

@@ -814,10 +814,11 @@ get_buffer_lines(
 }
 
 /*
- * "getbufline()" function
+ * "retlist" TRUE: "getbufline()" function
+ * "retlist" FALSE: "getbufoneline()" function
  */
-    void
+    static void
-f_getbufline(typval_T *argvars, typval_T *rettv)
+getbufline(typval_T *argvars, typval_T *rettv, int retlist)
 {
     linenr_T	lnum = 1;
     linenr_T	end = 1;
@@ -842,7 +843,25 @@ f_getbufline(typval_T *argvars, typval_T *rettv)
 	    end = tv_get_lnum_buf(&argvars[2], buf);
     }
 
-    get_buffer_lines(buf, lnum, end, TRUE, rettv);
+    get_buffer_lines(buf, lnum, end, retlist, rettv);
+}
+
+/*
+ * "getbufline()" function
+ */
+    void
+f_getbufline(typval_T *argvars, typval_T *rettv)
+{
+    getbufline(argvars, rettv, TRUE);
+}
+
+/*
+ * "getbufoneline()" function
+ */
+    void
+f_getbufoneline(typval_T *argvars, typval_T *rettv)
+{
+    getbufline(argvars, rettv, FALSE);
 }
 
 /*

src/evalfunc.c

@@ -1923,6 +1923,8 @@ static funcentry_T global_functions[] =
 			ret_list_dict_any,  f_getbufinfo},
     {"getbufline",	2, 3, FEARG_1,	    arg3_buffer_lnum_lnum,
 			ret_list_string,    f_getbufline},
+    {"getbufoneline",	2, 2, FEARG_1,	    arg2_buffer_lnum,
+			ret_string,	    f_getbufoneline},
     {"getbufvar",	2, 3, FEARG_1,	    arg3_buffer_string_any,
 			ret_any,	    f_getbufvar},
     {"getchangelist",	0, 1, FEARG_1,	    arg1_buffer,

src/proto/evalbuffer.pro

@@ -16,6 +16,7 @@ void f_bufwinnr(typval_T *argvars, typval_T *rettv);
 void f_deletebufline(typval_T *argvars, typval_T *rettv);
 void f_getbufinfo(typval_T *argvars, typval_T *rettv);
 void f_getbufline(typval_T *argvars, typval_T *rettv);
+void f_getbufoneline(typval_T *argvars, typval_T *rettv);
 void f_getline(typval_T *argvars, typval_T *rettv);
 void f_setbufline(typval_T *argvars, typval_T *rettv);
 void f_setline(typval_T *argvars, typval_T *rettv);

src/testdir/test_bufline.vim

@@ -11,7 +11,9 @@ func Test_setbufline_getbufline()
   hide
   call assert_equal(0, setbufline(b, 1, ['foo', 'bar']))
   call assert_equal(['foo'], getbufline(b, 1))
+  call assert_equal('foo', getbufoneline(b, 1))
   call assert_equal(['bar'], getbufline(b, '$'))
+  call assert_equal('bar', getbufoneline(b, '$'))
   call assert_equal(['foo', 'bar'], getbufline(b, 1, 2))
   exe "bd!" b
   call assert_equal([], getbufline(b, 1, 2))
@@ -35,8 +37,11 @@ func Test_setbufline_getbufline()
 
   call assert_equal(0, setbufline(b, 4, ['d', 'e']))
   call assert_equal(['c'], b->getbufline(3))
+  call assert_equal('c', b->getbufoneline(3))
   call assert_equal(['d'], getbufline(b, 4))
+  call assert_equal('d', getbufoneline(b, 4))
   call assert_equal(['e'], getbufline(b, 5))
+  call assert_equal('e', getbufoneline(b, 5))
   call assert_equal([], getbufline(b, 6))
   call assert_equal([], getbufline(b, 2, 1))
 

src/testdir/test_vim9_builtin.vim

@@ -1724,15 +1724,23 @@ def Test_getbufline()
   getbufline(-1, '$', '$')->assert_equal([])
   getbufline(-1, 1, '$')->assert_equal([])
 
+  getbufoneline('#', 1)->assert_equal(lines[0])
+
   assert_equal([7, 7, 7], getbufline('#', 1, '$')->map((_, _) => 7))
 
   assert_fails('getbufline("", "$a", "$b")', ['E1030: Using a String as a Number: "$a"', 'E1030: Using a String as a Number: "$a"'])
   assert_fails('getbufline("", "$", "$b")', ['E1030: Using a String as a Number: "$b"', 'E1030: Using a String as a Number: "$b"'])
   bwipe!
 
+  assert_fails('getbufoneline("", "$a")', ['E1030: Using a String as a Number: "$a"', 'E1030: Using a String as a Number: "$a"'])
+  bwipe!
+
   v9.CheckDefAndScriptFailure(['getbufline([], 2)'], ['E1013: Argument 1: type mismatch, expected string but got list<unknown>', 'E1220: String or Number required for argument 1'])
   v9.CheckDefAndScriptFailure(['getbufline("a", [])'], ['E1013: Argument 2: type mismatch, expected string but got list<unknown>', 'E1220: String or Number required for argument 2'])
   v9.CheckDefAndScriptFailure(['getbufline("a", 2, 0z10)'], ['E1013: Argument 3: type mismatch, expected string but got blob', 'E1220: String or Number required for argument 3'])
+
+  v9.CheckDefAndScriptFailure(['getbufoneline([], 2)'], ['E1013: Argument 1: type mismatch, expected string but got list<unknown>', 'E1220: String or Number required for argument 1'])
+  v9.CheckDefAndScriptFailure(['getbufoneline("a", [])'], ['E1013: Argument 2: type mismatch, expected string but got list<unknown>', 'E1220: String or Number required for argument 2'])
 enddef
 
 def Test_getbufvar()

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    916,
 /**/
     915,
 /**/