vim-patch:partial:8.2.3849: functions implementing reduce and map are too long

Problem:    Functions implementing reduce and map are too long.
Solution:   Use a function for each type of value.  Add a few more test cases
            and add to the help. (Yegappan Lakshmanan, closes vim/vim#9370)

https://github.com/vim/vim/commit/389b72196e6aaeafe3f907c73d271f2c6b931140

Partial port as this doesn't include handling for non-materialized List.

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

2 files changed, 14 insertions, 12 deletions

diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 6303d73db5..4b617763da 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -1635,8 +1635,8 @@ filter({expr1}, {expr2})                                              *filter()*
 		of the current item.  For a |Dictionary| |v:key| has the key
 		of the current item and for a |List| |v:key| has the index of
 		the current item.  For a |Blob| |v:key| has the index of the
-		current byte.
-
+		current byte. For a |String| |v:key| has the index of the
+		current character.
 		Examples: >vim
 			call filter(mylist, 'v:val !~ "OLD"')
 <		Removes the items where "OLD" appears. >vim
@@ -4080,7 +4080,8 @@ map({expr1}, {expr2})                                                    *map()*
 		of the current item.  For a |Dictionary| |v:key| has the key
 		of the current item and for a |List| |v:key| has the index of
 		the current item.  For a |Blob| |v:key| has the index of the
-		current byte.
+		current byte. For a |String| |v:key| has the index of the
+		current character.
 		Example: >vim
 			call map(mylist, '"> " .. v:val .. " <"')
 <		This puts "> " before and " <" after each item in "mylist".
@@ -5514,9 +5515,9 @@ readfile({fname} [, {type} [, {max}]])                              *readfile()*
 
 reduce({object}, {func} [, {initial}])                           *reduce()* *E998*
 		{func} is called for every item in {object}, which can be a
-		|String|, |List| or a |Blob|.  {func} is called with two arguments:
-		the result so far and current item.  After processing all
-		items the result is returned.
+		|String|, |List| or a |Blob|.  {func} is called with two
+		arguments: the result so far and current item.  After
+		processing all items the result is returned.
 
 		{initial} is the initial result.  When omitted, the first item
 		in {object} is used and {func} is first called for the second
diff --git a/runtime/lua/vim/_meta/vimfn.lua b/runtime/lua/vim/_meta/vimfn.lua
index 4fe9093666..17eda634e0 100644
--- a/runtime/lua/vim/_meta/vimfn.lua
+++ b/runtime/lua/vim/_meta/vimfn.lua
@@ -2017,8 +2017,8 @@ function vim.fn.filewritable(file) end
 --- of the current item.  For a |Dictionary| |v:key| has the key
 --- of the current item and for a |List| |v:key| has the index of
 --- the current item.  For a |Blob| |v:key| has the index of the
---- current byte.
----
+--- current byte. For a |String| |v:key| has the index of the
+--- current character.
 --- Examples: >vim
 ---   call filter(mylist, 'v:val !~ "OLD"')
 --- <Removes the items where "OLD" appears. >vim
@@ -4937,7 +4937,8 @@ function vim.fn.log10(expr) end
 --- of the current item.  For a |Dictionary| |v:key| has the key
 --- of the current item and for a |List| |v:key| has the index of
 --- the current item.  For a |Blob| |v:key| has the index of the
---- current byte.
+--- current byte. For a |String| |v:key| has the index of the
+--- current character.
 --- Example: >vim
 ---   call map(mylist, '"> " .. v:val .. " <"')
 --- <This puts "> " before and " <" after each item in "mylist".
@@ -6551,9 +6552,9 @@ function vim.fn.readdir(directory, expr) end
 function vim.fn.readfile(fname, type, max) end
 
 --- {func} is called for every item in {object}, which can be a
---- |String|, |List| or a |Blob|.  {func} is called with two arguments:
---- the result so far and current item.  After processing all
---- items the result is returned.
+--- |String|, |List| or a |Blob|.  {func} is called with two
+--- arguments: the result so far and current item.  After
+--- processing all items the result is returned.
 ---
 --- {initial} is the initial result.  When omitted, the first item
 --- in {object} is used and {func} is first called for the second