From 12099ed55e468e946c7669cfbf3029c72f0e15d4 Mon Sep 17 00:00:00 2001
From: Sajid Ali <30510036+s-sajid-ali@users.noreply.github.com>
Date: Thu, 9 Jul 2020 16:14:49 -0500
Subject: [PATCH] clear mpicc and friends before each build (#17450)

* clear mpi env vars
---
 lib/spack/spack/build_environment.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index 1b8aae31dc..7ef2126766 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -174,6 +174,14 @@ def clean_environment():
     for v in build_system_vars:
         env.unset(v)
 
+    # Unset mpi environment vars. These flags should only be set by
+    # mpi providers for packages with mpi dependencies
+    mpi_vars = [
+        'MPICC', 'MPICXX', 'MPIFC', 'MPIF77', 'MPIF90'
+    ]
+    for v in mpi_vars:
+        env.unset(v)
+
     build_lang = spack.config.get('config:build_language')
     if build_lang:
         # Override language-related variables. This can be used to force