vim-patch:8.2.0868: trim() always trims both ends

Problem:    trim() always trims both ends.
Solution:   Add an argument to only trim the beginning or end. (Yegappan
            Lakshmanan, closes vim/vim#6126)
https://github.com/vim/vim/commit/2245ae18e3480057f98fc0e5d9f18091f32a5de0

4 files changed, 69 insertions, 35 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 201bb07cd2..392047b565 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2468,7 +2468,8 @@ tolower({expr})			String	the String {expr} switched to lowercase
 toupper({expr})			String	the String {expr} switched to uppercase
 tr({src}, {fromstr}, {tostr})	String	translate chars of {src} in {fromstr}
 					to chars in {tostr}
-trim({text} [, {mask}])		String	trim characters in {mask} from {text}
+trim({text} [, {mask} [, {dir}]])
+				String	trim characters in {mask} from {text}
 trunc({expr})			Float	truncate Float {expr}
 type({name})			Number	type of variable {name}
 undofile({name})		String	undo file name for {name}
@@ -9048,21 +9049,28 @@ tr({src}, {fromstr}, {tostr})				*tr()*
 			echo tr("<blob>", "<>", "{}")
 <		returns "{blob}"
 
-trim({text} [, {mask}])						*trim()*
+trim({text} [, {mask} [, {dir}]])				*trim()*
 		Return {text} as a String where any character in {mask} is
-		removed from the beginning and  end of {text}.
+		removed from the beginning and/or end of {text}.
 		If {mask} is not given, {mask} is all characters up to 0x20,
 		which includes Tab, space, NL and CR, plus the non-breaking
 		space character 0xa0.
-		This code deals with multibyte characters properly.
-
+		The optional {dir} argument specifies where to remove the
+		characters:
+			0	remove from the beginning and end of {text}
+			1	remove only at the beginning of {text}
+			2	remove only at the end of {text}
+		When omitted both ends are trimmed.
+		This function deals with multibyte characters properly.
 		Examples: >
 			echo trim("   some text ")
 <		returns "some text" >
 			echo trim("  \r\t\t\r RESERVE \t\n\x0B\xA0") . "_TAIL"
 <		returns "RESERVE_TAIL" >
 			echo trim("rm<Xrm<>X>rrm", "rm<>")
-<		returns "Xrm<>X" (characters in the middle are not removed)
+<		returns "Xrm<>X" (characters in the middle are not removed) >
+			echo trim("  vim  ", " ", 2)
+<		returns "  vim"
 
 trunc({expr})							*trunc()*
 		Return the largest integral value with magnitude less than or
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index 372c950825..11f6a350e4 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -371,7 +371,7 @@ return {
     tolower={args=1},
     toupper={args=1},
     tr={args=3},
-    trim={args={1,2}},
+    trim={args={1,3}},
     trunc={args=1, func="float_op_wrapper", data="&trunc"},
     type={args=1},
     undofile={args=1},
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 6c3802143f..861743eb7d 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -10823,52 +10823,72 @@ static void f_trim(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   const char_u *prev;
   const char_u *p;
   int c1;
+  int dir = 0;
 
   rettv->v_type = VAR_STRING;
+  rettv->vval.v_string = NULL;
   if (head == NULL) {
-    rettv->vval.v_string = NULL;
     return;
   }
 
   if (argvars[1].v_type == VAR_STRING) {
     mask = (const char_u *)tv_get_string_buf_chk(&argvars[1], buf2);
+    if (argvars[2].v_type != VAR_UNKNOWN) {
+      bool error = false;
+      // leading or trailing characters to trim
+      dir = (int)tv_get_number_chk(&argvars[2], &error);
+      if (error) {
+        return;
+      }
+      if (dir < 0 || dir > 2) {
+        emsgf(_(e_invarg2), tv_get_string(&argvars[2]));
+        return;
+      }
+    }
   }
 
-  while (*head != NUL) {
-    c1 = PTR2CHAR(head);
-    if (mask == NULL) {
-      if (c1 > ' ' && c1 != 0xa0) {
-        break;
-      }
-    } else {
-      for (p = mask; *p != NUL; MB_PTR_ADV(p)) {
-        if (c1 == PTR2CHAR(p)) {
+  if (dir == 0 || dir == 1) {
+    // Trim leading characters
+    while (*head != NUL) {
+      c1 = PTR2CHAR(head);
+      if (mask == NULL) {
+        if (c1 > ' ' && c1 != 0xa0) {
+          break;
+        }
+      } else {
+        for (p = mask; *p != NUL; MB_PTR_ADV(p)) {
+          if (c1 == PTR2CHAR(p)) {
+            break;
+          }
+        }
+        if (*p == NUL) {
           break;
         }
       }
-      if (*p == NUL) {
-        break;
-      }
+      MB_PTR_ADV(head);
     }
-    MB_PTR_ADV(head);
   }
 
-  for (tail = head + STRLEN(head); tail > head; tail = prev) {
-    prev = tail;
-    MB_PTR_BACK(head, prev);
-    c1 = PTR2CHAR(prev);
-    if (mask == NULL) {
-      if (c1 > ' ' && c1 != 0xa0) {
-        break;
-      }
-    } else {
-      for (p = mask; *p != NUL; MB_PTR_ADV(p)) {
-        if (c1 == PTR2CHAR(p)) {
+  tail = head + STRLEN(head);
+  if (dir == 0 || dir == 2) {
+    // Trim trailing characters
+    for (; tail > head; tail = prev) {
+      prev = tail;
+      MB_PTR_BACK(head, prev);
+      c1 = PTR2CHAR(prev);
+      if (mask == NULL) {
+        if (c1 > ' ' && c1 != 0xa0) {
+          break;
+        }
+      } else {
+        for (p = mask; *p != NUL; MB_PTR_ADV(p)) {
+          if (c1 == PTR2CHAR(p)) {
+            break;
+          }
+        }
+        if (*p == NUL) {
           break;
         }
-      }
-      if (*p == NUL) {
-        break;
       }
     }
   }
diff --git a/src/nvim/testdir/test_functions.vim b/src/nvim/testdir/test_functions.vim
index 8fa70a5313..00f0126582 100644
--- a/src/nvim/testdir/test_functions.vim
+++ b/src/nvim/testdir/test_functions.vim
@@ -1083,6 +1083,12 @@ func Test_trim()
   call assert_equal("", trim("", ""))
   call assert_equal("a", trim("a", ""))
   call assert_equal("", trim("", "a"))
+  call assert_equal("vim", trim("  vim  ", " ", 0))
+  call assert_equal("vim  ", trim("  vim  ", " ", 1))
+  call assert_equal("  vim", trim("  vim  ", " ", 2))
+  call assert_fails('call trim("  vim  ", " ", [])', 'E745:')
+  call assert_fails('call trim("  vim  ", " ", -1)', 'E475:')
+  call assert_fails('call trim("  vim  ", " ", 3)', 'E475:')
 
   let chars = join(map(range(1, 0x20) + [0xa0], {n -> nr2char(n)}), '')
   call assert_equal("x", trim(chars . "x" . chars))