Support for building Pmix with Debian/Ubuntu external dependencies (#32690)

* Debian like distros use multiarch implementation spec
https://wiki.ubuntu.com/MultiarchSpec
Instead of being limited to /usr/lib64, architecture based
lib directories are used. For instance, under ubuntu a library package
on x86_64 installs binaries under /usr/lib/x86_64-linux-gnu.
Building pmix with external dependencies like hwloc or libevent
fail as with prefix set to /usr, that prefix works for
headers and binaries but does not work for libraries. The default
location for library /usr/lib64 does not hold installed binaries.
Pmix build options --with-libevent and --with-libhwloc allow us to
specify dependent library locations. This commit is an effort to
highlight and resolve such an issue when a users want to use Debian like
distro library packages and use spack to build pmix.
There maybe other packages that might be impacted in a similar way.

* Adding libs property to hwloc and libevent and some cleanups to pmix patch

* Fixing style and adding comment on Pmix' 32-bit hwloc version detection issue

3 files changed, 36 insertions, 0 deletions

diff --git a/var/spack/repos/builtin/packages/hwloc/package.py b/var/spack/repos/builtin/packages/hwloc/package.py
index 4c67d3e32b..706328f7c5 100644
--- a/var/spack/repos/builtin/packages/hwloc/package.py
+++ b/var/spack/repos/builtin/packages/hwloc/package.py
@@ -146,6 +146,11 @@ class Hwloc(AutotoolsPackage, CudaPackage, ROCmPackage):
         url = "https://download.open-mpi.org/release/hwloc/v{0}/hwloc-{1}.tar.gz"
         return url.format(version.up_to(2), version)
 
+    @property
+    def libs(self):
+        libs = find_libraries("libhwloc", root=self.prefix, shared=True, recursive=True)
+        return LibraryList(libs)
+
     def configure_args(self):
         args = []
 
diff --git a/var/spack/repos/builtin/packages/libevent/package.py b/var/spack/repos/builtin/packages/libevent/package.py
index 9042a566d4..2a49064d95 100644
--- a/var/spack/repos/builtin/packages/libevent/package.py
+++ b/var/spack/repos/builtin/packages/libevent/package.py
@@ -49,6 +49,11 @@ class Libevent(AutotoolsPackage):
 
         return url.format(version)
 
+    @property
+    def libs(self):
+        libs = find_libraries("libevent", root=self.prefix, shared=True, recursive=True)
+        return LibraryList(libs)
+
     def configure_args(self):
         spec = self.spec
         configure_args = []
diff --git a/var/spack/repos/builtin/packages/pmix/package.py b/var/spack/repos/builtin/packages/pmix/package.py
index 999535b92f..39433e3f30 100644
--- a/var/spack/repos/builtin/packages/pmix/package.py
+++ b/var/spack/repos/builtin/packages/pmix/package.py
@@ -3,6 +3,7 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import os
+import platform
 
 from spack.package import *
 
@@ -97,6 +98,18 @@ class Pmix(AutotoolsPackage):
         perl = which("perl")
         perl("./autogen.pl")
 
+    def find_external_lib_path(self, pkg_name, path_match_str=""):
+        spec = self.spec
+        tgt_libpath = ""
+        dir_list = spec[pkg_name].libs
+        for entry in dir_list:
+            if path_match_str == "" or (path_match_str != "" and path_match_str in entry):
+                tgt_libpath = entry
+                break
+        path_list = tgt_libpath.split(os.sep)
+        del path_list[-1]
+        return (os.sep).join(path_list)
+
     def configure_args(self):
         spec = self.spec
 
@@ -105,6 +118,19 @@ class Pmix(AutotoolsPackage):
         config_args.append("--with-libevent=" + spec["libevent"].prefix)
         config_args.append("--with-hwloc=" + spec["hwloc"].prefix)
 
+        # As of 09/22/22 pmix build does not detect the hwloc version
+        # for 32-bit architecture correctly. Since, we have only been
+        # able to test on 64-bit architecture, we are keeping this
+        # check for "64" in place. We will need to re-visit this when we
+        # have the fix in Pmix for 32-bit library version detection
+        if "64" in platform.machine():
+            if spec["libevent"].external_path:
+                dep_libpath = self.find_external_lib_path("libevent", "64")
+                config_args.append("--with-libevent-libdir=" + dep_libpath)
+            if spec["hwloc"].external_path:
+                dep_libpath = self.find_external_lib_path("hwloc", "64")
+                config_args.append("--with-hwloc-libdir=" + dep_libpath)
+
         config_args.extend(self.enable_or_disable("python-bindings", variant="python"))
 
         config_args.extend(