From 5b59ab3d9cff77cf62aeb342a3c02297311aa49e Mon Sep 17 00:00:00 2001
From: Mahmoud Al-Qudsi <mqudsi@neosmart.net>
Date: Wed, 19 Sep 2018 18:10:38 -0500
Subject: [PATCH] Add workaround to env_get_pwd_slash() for cases where PWD is
 not set

There's been no reproducible case entered for #5080, but the stack trace
indicates the problem is with env_get_pwd_slash() returning an empty
string, which isn't a string that terminates in `/`.

In addition to making the failure case to return the path `./` (which
has the benefit of having the same meaning as $PWD), trying a little bit
harder to retrieve the real PWD by using getcwd(3). While
get_current_dir(3) is documented as relying on PWD, getcwd(3) does not
mention any such caveats, so it's possible that it will work even if
something is breaking PWD.

Just a thought, but it's possible if due to some recursion PWD surpassed
some predetermined value (maybe PATH_MAX) that PWD (on certain platforms
or under certain enivronments) won't be set (hence the code that deals
with ERANGE errors from the getcwd(3) call).

Closes #5080.
---
 src/env.cpp | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/env.cpp b/src/env.cpp
index 77f65b7bc..fc00031f1 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -698,10 +698,36 @@ void env_set_read_limit() {
 
 wcstring env_get_pwd_slash() {
     auto pwd_var = env_get(L"PWD");
-    if (pwd_var.missing_or_empty()) {
-        return L"";
+    wcstring pwd;
+    if (!pwd_var.missing_or_empty()) {
+        pwd = pwd_var->as_string();
     }
-    wcstring pwd = pwd_var->as_string();
+    else {
+        // Not sure how we can end up here, but it's possible.
+        // See https://github.com/fish-shell/fish-shell/issues/5080
+        // Perhaps it can happen on some platforms if the path is too long?
+        std::vector<char> path;
+        bool cwd_success = false;
+        for (int i = 1; !cwd_success && i <= 10; ++i) {
+            path.resize(PATH_MAX * i);
+            if (getcwd(&path[0], PATH_MAX * i) == nullptr) {
+                if (errno == ERANGE) {
+                    // buffer is not big enough, try again (up to a point)
+                    continue;
+                }
+                debug(1, "getcwd() failed with errno %d", errno);
+                // . but with a trailing slash, because that's what this function does
+                return L"./";
+            }
+            cwd_success = true;
+        }
+        if (!cwd_success) {
+            debug(1, "getcwd() path too long!");
+            return L"./";
+        }
+        pwd = str2wcstring(path.data());
+    }
+
     if (!string_suffixes_string(L"/", pwd)) {
         pwd.push_back(L'/');
     }