find_libraries searches lib and lib64 before prefix (#11958)

The default library search for a package checks the lib/ and lib64/
directories for libraries before the root prefix, in order to save
time when searching for libraries provided by externals (which e.g.
may have '/usr/' as their root).

This moves that logic into the "find_libraries" utility method so
packages implementing their own custom library search logic can
benefit from it.

This also updates packages which appear to be replicating this logic
exactly, replacing it with a single call to "find_libraries".

lib/spack/llnl/util/filesystem.py

@@ -1389,7 +1389,25 @@ def find_libraries(libraries, root, shared=True, recursive=False):
     # List of libraries we are searching with suffixes
     libraries = ['{0}.{1}'.format(lib, suffix) for lib in libraries]
 
-    return LibraryList(find(root, libraries, recursive))
+    if not recursive:
+        # If not recursive, look for the libraries directly in root
+        return LibraryList(find(root, libraries, False))
+
+    # To speedup the search for external packages configured e.g. in /usr,
+    # perform first non-recursive search in root/lib then in root/lib64 and
+    # finally search all of root recursively. The search stops when the first
+    # match is found.
+    for subdir in ('lib', 'lib64'):
+        dirname = join_path(root, subdir)
+        if not os.path.isdir(dirname):
+            continue
+        found_libs = find(dirname, libraries, False)
+        if found_libs:
+            break
+    else:
+        found_libs = find(root, libraries, True)
+
+    return LibraryList(found_libs)
 
 
 @memoized

lib/spack/spack/spec.py

@@ -725,28 +725,18 @@ def _libs_default_handler(descriptor, spec, cls):
     if not name.startswith('lib'):
         name = 'lib' + name
 
-    # To speedup the search for external packages configured e.g. in /usr,
-    # perform first non-recursive search in prefix.lib then in prefix.lib64 and
-    # finally search all of prefix recursively. The search stops when the first
-    # match is found.
-    prefix = spec.prefix
-    search_paths = [(prefix.lib, False), (prefix.lib64, False), (prefix, True)]
-
     # If '+shared' search only for shared library; if '~shared' search only for
     # static library; otherwise, first search for shared and then for static.
     search_shared = [True] if ('+shared' in spec) else \
         ([False] if ('~shared' in spec) else [True, False])
 
     for shared in search_shared:
-        for path, recursive in search_paths:
-            libs = find_libraries(
-                name, root=path, shared=shared, recursive=recursive
-            )
-            if libs:
-                return libs
+        libs = find_libraries(name, spec.prefix, shared=shared, recursive=True)
+        if libs:
+            return libs
 
     msg = 'Unable to recursively locate {0} libraries in {1}'
-    raise NoLibrariesError(msg.format(spec.name, prefix))
+    raise NoLibrariesError(msg.format(spec.name, spec.prefix))
 
 
 class ForwardQueryToPackage(object):