From 44022e65c2237bc3dd01b0fc9ccbf8c2dcbdfc51 Mon Sep 17 00:00:00 2001
From: Mahmoud Al-Qudsi <mqudsi@neosmart.net>
Date: Sun, 25 Aug 2019 18:29:46 -0500
Subject: [PATCH] Revert "Remove the WSL warning"

This reverts commit 5101bdeb9f2d2d0a362619edde3da8c1b9cd7101.
---
 src/common.cpp | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/common.cpp b/src/common.cpp
index a775314ce..54856d3af 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -16,7 +16,6 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/time.h>
-#include <sys/utsname.h>
 #include <termios.h>
 #include <unistd.h>
 #include <wctype.h>
@@ -32,6 +31,11 @@
 #include <sys/ioctl.h>
 #endif
 
+#ifdef __linux__
+// Includes for WSL detection
+#include <sys/utsname.h>
+#endif
+
 #ifdef __FreeBSD__
 #include <sys/sysctl.h>
 #elif __APPLE__
@@ -153,10 +157,29 @@ bool is_windows_subsystem_for_linux() {
 #elif not defined(__linux__)
     return false;
 #else
+    // We are purposely not using std::call_once as it may invoke locking, which is an unnecessary
+    // overhead since there's no actual race condition here - even if multiple threads call this
+    // routine simultaneously the first time around, we just end up needlessly querying uname(2) one
+    // more time.
+
     static bool wsl_state = []() {
-        utsname info{};
+        utsname info;
         uname(&info);
-        return std::strstr(info.release, "Microsoft") != nullptr;
+
+        // Sample utsname.release under WSL: 4.4.0-17763-Microsoft
+        if (std::strstr(info.release, "Microsoft") != nullptr) {
+            const char *dash = std::strchr(info.release, '-');
+            if (dash == nullptr || strtod(dash + 1, nullptr) < 17763) {
+                debug(1,
+                      "This version of WSL is not supported and fish will probably not work "
+                      "correctly!\n"
+                      "Please upgrade to Windows 10 1809 (17763) or higher to use fish!");
+            }
+
+            return true;
+        } else {
+            return false;
+        }
     }();
 
     // Subsequent calls to this function may take place after fork() and before exec() in