vim-patch:8.1.2115: MS-Windows: shell commands fail if &shell contains a space

Problem:    MS-Windows: shell commands fail if &shell contains a space.
Solution:   Use quotes instead of escaping. (closes vim/vim#4920)
https://github.com/vim/vim/commit/2efc44b3f0b6bd8307cb281af095e08e15ab1c24

Always double-quote &shell if it contains a space.
Neovim does not support escaping space with backslash, unlike Vim.

N/A patches for version.c:

vim-patch:8.0.1455: if $SHELL contains a space then 'shell' is incorrect

Problem:    If $SHELL contains a space then the default value of 'shell' is
            incorrect. (Matthew Horan)
Solution:   Escape spaces in $SHELL. (Christian Brabandt, closes vim/vim#459)
https://github.com/vim/vim/commit/4bfa8af14142e54f509048239f4e8596911f56aa

vim-patch:8.2.1194: test failure because shell prompt differs

Problem:    Test failure because shell prompt differs.
Solution:   Set the shell prompt.
https://github.com/vim/vim/commit/a4dc6f92bb29b00783f8945bbe1101e837b6ad3c

1 files changed, 11 insertions, 5 deletions

diff --git a/src/nvim/option.c b/src/nvim/option.c
index 146bce8cc0..6149331763 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -652,7 +652,14 @@ void set_init_1(bool clean_arg)
   {
     const char *shell = os_getenv("SHELL");
     if (shell != NULL) {
-      set_string_default("sh", (char *) shell, false);
+      if (vim_strchr((const char_u *)shell, ' ') != NULL) {
+        const size_t len = strlen(shell) + 3;  // two quotes and a trailing NUL
+        char *const cmd = xmalloc(len);
+        snprintf(cmd, len, "\"%s\"", shell);
+        set_string_default("sh", cmd, true);
+      } else {
+        set_string_default("sh", (char *)shell, false);
+      }
     }
   }
 
@@ -987,10 +994,9 @@ static void set_string_default(const char *name, char *val, bool allocated)
       xfree(options[opt_idx].def_val[VI_DEFAULT]);
     }
 
-    options[opt_idx].def_val[VI_DEFAULT] = (char_u *) (
-        allocated
-        ? (char_u *) val
-        : (char_u *) xstrdup(val));
+    options[opt_idx].def_val[VI_DEFAULT] = allocated
+        ? (char_u *)val
+        : (char_u *)xstrdup(val);
     options[opt_idx].flags |= P_DEF_ALLOCED;
   }
 }