Issue #16537: Check whether self.extensions is empty in setup.py.

Patch by Jonathan Hosmer.

Misc/ACKS

@@ -592,6 +592,7 @@ Randall Hopper
 Nadav Horesh
 Alon Horev
 Jan Hosang
+Jonathan Hosmer
 Alan Hourihane
 Ken Howard
 Brad Howes

Misc/NEWS

@@ -977,6 +977,9 @@ IDLE
 Build
 -----
 
+- Issue #16537: Check whether self.extensions is empty in setup.py. Patch by
+  Jonathan Hosmer.
+
 - Issue #22359: Remove incorrect uses of recursive make.  Patch by Jonas
   Wagner.
 

setup.py

@@ -263,6 +263,8 @@ class PyBuildExt(build_ext):
         for ext in self.extensions:
             self.check_extension_import(ext)
 
+        longest = 0
+        if self.extensions:
             longest = max([len(e.name) for e in self.extensions])
         if self.failed or self.failed_on_import:
             all_failed = self.failed + self.failed_on_import