Handle permission errors while generating paths on Darwin

On Darwin, Nix may invoke SCons in a sandbox which lacks access to
/etc/paths.d. Handle PermissionError while iterating through
/etc/paths.d to support sandboxed environments such as Nix.

CHANGES.txt

@@ -50,6 +50,11 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Some manpage cleanup for the gettext and pdf/ps builders.
     - Some clarifications in the User Guide "Environments" chapter.
 
+  From Alex James:
+    - On Darwin, PermissionErrors are now handled while trying to access
+      /etc/paths.d. This may occur if SCons is invoked in a sandboxed
+      environment (such as Nix).
+
 
 RELEASE 4.8.1 -  Tue, 03 Sep 2024 17:22:20 -0700
 

RELEASE.txt

@@ -46,6 +46,10 @@ FIXES
 - Fix a problem with compilation_db component initialization - the
   entries for assembler files were not being set up correctly.
 
+- On Darwin, PermissionErrors are now handled while trying to access
+  /etc/paths.d. This may occur if SCons is invoked in a sandboxed environment
+  (such as Nix).
+
 IMPROVEMENTS
 ------------
 

SCons/Platform/darwin.py

@@ -46,7 +46,7 @@ def generate(env) -> None:
     # make sure this works on Macs with Tiger or earlier
     try:
         dirlist = os.listdir('/etc/paths.d')
-    except FileNotFoundError:
+    except (FileNotFoundError, PermissionError):
         dirlist = []
 
     for file in dirlist: