has('wsl') porting for vim (供養)

has_wsl.patch

diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 72e2cf13f..833a39a11 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -10445,6 +10445,7 @@ xpm			Compiled with pixmap support.
 xpm_w32			Compiled with pixmap support for Win32. (Only for
 			backward compatibility. Use "xpm" instead.)
 xsmp			Compiled with X session management support.
+wsl			Vim is running on WSL (Windows Subsystem for Linux).
 xsmp_interact		Compiled with interactive X session management support.
 xterm_clipboard		Compiled with support for xterm clipboard.
 xterm_save		Compiled with support for saving and restoring the
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 35b8984c3..00bf0e56e 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -5260,6 +5260,9 @@ f_has(typval_T *argvars, typval_T *rettv)
 	char *name;
 	short present;
     } has_item_T;
+#if defined(__linux__) && defined(HAVE_SYS_UTSNAME_H)
+    char_u	kernel_release[256];
+#endif
     static has_item_T has_list[] =
     {
 	{"amiga",
@@ -6548,6 +6551,20 @@ f_has(typval_T *argvars, typval_T *rettv)
 	    x = TRUE;
 #ifdef FEAT_CLIPBOARD
 	    n = clip_star.available;
+#endif
+	}
+	else if (STRICMP(name, "wsl") == 0)
+	{
+	    x = TRUE;
+#if defined(__linux__) && defined(HAVE_SYS_UTSNAME_H)
+	    mch_get_kernel_release(kernel_release, 256);
+	    vim_strup(kernel_release);
+	    if (strstr((char *)kernel_release, "MICROSOFT") != NULL)
+	        n = TRUE;
+	    else
+	        n = FALSE;
+#else
+	    n = FALSE;
 #endif
 	}
     }
diff --git a/src/os_unix.c b/src/os_unix.c
index b786f8df0..d5ed493c4 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -2526,6 +2526,21 @@ mch_get_host_name(char_u *s, int len)
 }
 #endif // HAVE_SYS_UTSNAME_H
 
+/*
+ * Insert kernel release is s[len] (like uname(1))
+ */
+#ifdef HAVE_SYS_UTSNAME_H
+    void
+mch_get_kernel_release(char_u *s, int len) {
+    struct utsname vutsname;
+
+    if (uname(&vutsname) < 0)
+        *s = NUL;
+    else
+        vim_strncpy(s, (char_u *)vutsname.release, len - 1);
+}
+#endif
+
 /*
  * return process ID
  */
diff --git a/src/proto/os_unix.pro b/src/proto/os_unix.pro
index 7dd8e231b..ace67ddd7 100644
--- a/src/proto/os_unix.pro
+++ b/src/proto/os_unix.pro
@@ -27,6 +27,7 @@ int vim_is_fastterm(char_u *name);
 int mch_get_user_name(char_u *s, int len);
 int mch_get_uname(uid_t uid, char_u *s, int len);
 void mch_get_host_name(char_u *s, int len);
+void mch_get_kernel_release(char_u *s, int len);
 long mch_get_pid(void);
 int mch_process_running(long pid);
 int mch_dirname(char_u *buf, int len);