Staging: determine extensions from nonstandard URLs (#31027)

Fixes #31021

With #25185, we no longer default to using tar when we can't
determine the extension type, opting to fail instead.

This broke fetching for the pcre package, where we couldn't determine
the extension. To determine the extension, we were attempting to
extract it from the destination filename; however, this file name
may omit details of the origin URL that are required to determine the
extension, so instead we examine the URL directly.

This also updates the decompressor_for method not to set ext=None
by default: it must now always be set by the caller.

lib/spack/spack/fetch_strategy.py

@@ -521,7 +521,7 @@ def expand(self):
                 "Failed on expand() for URL %s" % self.url)
 
         if not self.extension:
-            self.extension = extension(self.archive_file)
+            self.extension = extension(self.url)
 
         if self.stage.expanded:
             tty.debug('Source already staged to %s' % self.stage.source_path)

lib/spack/spack/util/compression.py

@@ -246,7 +246,7 @@ def _7zip(archive_file):
     return outfile
 
 
-def decompressor_for(path, ext=None):
+def decompressor_for(path, ext):
     """Returns a function pointer to appropriate decompression
     algorithm based on extension type.
 
@@ -254,9 +254,6 @@ def decompressor_for(path, ext=None):
         path (str): path of the archive file requiring decompression
         ext (str): Extension of archive file
     """
-    if not ext:
-        ext = extension(path)
-
     if not allowed_archive(ext):
         raise CommandNotFoundError("Cannot extract archive, \
 unrecognized file extension: '%s'" % ext)