execvpe.patch

diff --git a/hphp/hack/hhi/hsl/ext_hsl_os_subprocesses.hhi b/hphp/hack/hhi/hsl/ext_hsl_os_subprocesses.hhi
index 59f4eb477b..9a0d09b546 100644
--- a/hphp/hack/hhi/hsl/ext_hsl_os_subprocesses.hhi
+++ b/hphp/hack/hhi/hsl/ext_hsl_os_subprocesses.hhi
@@ -15,6 +15,7 @@ use type HH\Lib\OS\FileDescriptor;
 type ForkAndExecveOptions = shape(
   ?'cwd' => string,
   ?'setsid' => bool,
+  ?'execvpe' => bool,
   ?'setpgid' => int,
 );
 
diff --git a/hphp/runtime/ext/hsl/ext_hsl_os.cpp b/hphp/runtime/ext/hsl/ext_hsl_os.cpp
index 4de7bb8245..0b255004d8 100644
--- a/hphp/runtime/ext/hsl/ext_hsl_os.cpp
+++ b/hphp/runtime/ext/hsl/ext_hsl_os.cpp
@@ -910,7 +910,8 @@ Object HHVM_FUNCTION(HSL_os_poll_async,
 const StaticString
   s_cwd("cwd"),
   s_setsid("setsid"),
-  s_setpgid("setpgid");
+  s_setpgid("setpgid"),
+  s_execvpe("execvpe");
 
 int64_t HHVM_FUNCTION(HSL_os_fork_and_execve,
                       const String& path,
@@ -955,6 +956,16 @@ int64_t HHVM_FUNCTION(HSL_os_fork_and_execve,
     flags |= Process::FORK_AND_EXECVE_FLAG_SETPGID;
   }
 
+  if (options.exists(s_execvpe)) {
+    const auto& val = options[s_execvpe];
+    if (!val.isBoolean()) {
+      throw_errno_exception(EINVAL, "'execvpe' option must be a bool");
+    }
+    if (val.asBooleanVal()) {
+      flags |= Process::FORK_AND_EXECVE_FLAG_EXECVPE;
+    }
+  }
+
   auto vec_str_to_cpp_arr = ([] (const Array& vec) {
     std::vector<std::string> arr;
     for (ArrayIter iter(vec); iter; ++iter) {
diff --git a/hphp/util/process.cpp b/hphp/util/process.cpp
index 5300b3e519..22d98dbee5 100644
--- a/hphp/util/process.cpp
+++ b/hphp/util/process.cpp
@@ -32,6 +32,10 @@
 #include <folly/portability/Unistd.h>
 #endif
 
+#ifdef __APPLE__
+#include <crt_externs.h>
+#endif
+
 #include <folly/Conv.h>
 #include <folly/Format.h>
 #include <folly/ScopeGuard.h>
@@ -571,10 +575,43 @@ pid_t Process::ForkAndExecve(
     }
 
     char** argv_arr = build_cstrarr(argv);
-    char** envp_arr = build_cstrarr(envp);
+    char** envp_arr = nullptr;
     SCOPE_EXIT { free(argv_arr); free(envp_arr); };
 
-    execve(path.c_str(), argv_arr, envp_arr);
+    if (flags & Process::FORK_AND_EXECVE_FLAG_EXECVPE) {
+      // we could use real `execvpe` on linux, but let's just use the emulation
+      // everywhere so we have reliable cross-platform behavior and testability
+
+      // We could either:
+      // - use `execve()` and implement our own $PATH behavior
+      // - use `execvp()` and implement our own envp behavior
+      // The latter seems less likely to lead to accidental problems, so let's
+      // do that.
+
+#if defined(__linux__)
+      clearenv();
+#elif defined(__APPLE__)
+      // `environ` in MacOS-speak
+      *(_NSGetEnviron()) = nullptr;
+#else
+      static_assert(false, "Unsupported platform");
+#endif
+      for (const auto& var : envp) {
+        // Need a null-terminated, mutable char*
+        char* buf = (char*) malloc(var.length() + 1);
+        buf[var.length()] = 0;
+        memcpy(buf, var.c_str(), var.length());
+
+        if (putenv(buf) != 0) {
+          dprintf(fork_w, "%s %d", "putenv", errno);
+          _Exit(1);
+        }
+      }
+      execvp(path.c_str(), argv_arr);
+    } else {
+      envp_arr = build_cstrarr(envp);
+      execve(path.c_str(), argv_arr, envp_arr);
+    }
     dprintf(fork_w, "%s %d", "execve", errno);
     _Exit(1);
   }
@@ -621,6 +658,9 @@ pid_t Process::ForkAndExecve(
   if (failed_call == "execve") {
     return -5;
   }
+  if (failed_call == "putenv") {
+    return -6;
+  }
   return -9999;
 }
 
diff --git a/hphp/util/process.h b/hphp/util/process.h
index 9fd067d6d3..55c1ac0bc4 100644
--- a/hphp/util/process.h
+++ b/hphp/util/process.h
@@ -258,6 +258,7 @@ struct Process {
   static const int FORK_AND_EXECVE_FLAG_NONE    = 0;
   static const int FORK_AND_EXECVE_FLAG_SETPGID = 1 << 0;
   static const int FORK_AND_EXECVE_FLAG_SETSID  = 1 << 1;
+  static const int FORK_AND_EXECVE_FLAG_EXECVPE = 1 << 2;
 
   /** Opens a process with the given arguments, environment, working directory,
    * and file descriptors.