Only inherit a PWD if it resolves to "."

Fixes #5647

CHANGELOG.md

@@ -1,3 +1,12 @@
+# fish 3.0.2
+
+This release of fish contains the following ixes:
+
+### Fixes and improvements
+
+- The PWD environment variable is now ignored if it does not resolve to the true working directory (#5647).
+
+
 # fish 3.0.1 (released February 11, 2019)
 
 This release of fish fixes a number of major issues discovered in fish 3.0.0.

src/env.cpp

@@ -960,12 +960,13 @@ void env_init(const struct config_paths_t *paths /* or NULL */) {
         }
     }
 
-    // initialize the PWD variable if necessary
-    // Note we may inherit a virtual PWD that doesn't match what getcwd would return; respect that.
-    // Note we treat PWD as read-only so it was not set in vars.
-    const char *incoming_pwd = getenv("PWD");
-    if (incoming_pwd && incoming_pwd[0]) {
-        env_set_one(L"PWD",  ENV_EXPORT | ENV_GLOBAL, str2wcstring(incoming_pwd));
+    // Note we may inherit a virtual PWD that doesn't match what getcwd would return; respect that
+    // if and only if it matches getcwd (#5647). Note we treat PWD as read-only so it was not set in
+    // vars.
+    const char *incoming_pwd_cstr = getenv("PWD");
+    wcstring incoming_pwd = incoming_pwd_cstr ? str2wcstring(incoming_pwd_cstr) : wcstring{};
+    if (!incoming_pwd.empty() && paths_are_same_file(incoming_pwd, L".")) {
+        env_set_one(L"PWD", ENV_EXPORT | ENV_GLOBAL, std::move(incoming_pwd));
     } else {
         env_set_pwd_from_getcwd();
     }

tests/cd.in

@@ -46,8 +46,22 @@ mkdir -p $base/realhome
 set fish_path $PWD/../test/root/bin/fish
 ln -s $base/realhome $base/linkhome
 cd $base/linkhome
+set -l real_getcwd (pwd -P)
 env HOME=$base/linkhome $fish_path -c 'echo PWD is $PWD'
 
+# Do not inherit a virtual PWD that fails to resolve to getcwd (#5647)
+
+env HOME=$base/linkhome PWD=/tmp $fish_path -c 'echo $PWD' | read output_pwd
+test (realpath $output_pwd) = $real_getcwd
+and echo "BogusPWD test 1 succeeded"
+or echo "BogusPWD test 1 failed: $output_pwd vs $real_getcwd"
+
+env HOME=$base/linkhome PWD=/path/to/nowhere $fish_path -c 'echo $PWD' | read output_pwd
+test (realpath $output_pwd) = $real_getcwd
+and echo "BogusPWD test 2 succeeded"
+or echo "BogusPWD test 2 failed: $output_pwd vs $real_getcwd"
+
+
 # cd back before removing the test directory again.
 cd $oldpwd
 rm -Rf $base

tests/cd.out

@@ -21,3 +21,5 @@ cd:
 ####################
 # Virtual PWD inheritance
 PWD is /tmp/cdcomp_test/linkhome
+BogusPWD test 1 succeeded
+BogusPWD test 2 succeeded