default to disable package caching during build

src/rez/config.py

@@ -406,6 +406,7 @@ def _parse_env_var(self, value):
     "package_cache_clean_limit":                    Float,
     "allow_unversioned_packages":                   Bool,
     "rxt_as_yaml":                                  Bool,
+    "package_cache_during_build":                   Bool,
     "package_cache_local":                          Bool,
     "package_cache_same_device":                    Bool,
     "color_enabled":                                ForceOrBool,

src/rez/resolved_context.py

@@ -153,7 +153,7 @@ def __init__(self, package_requests, verbosity=0, timestamp=None,
                  package_filter=None, package_orderers=None, max_fails=-1,
                  add_implicit_packages=True, time_limit=-1, callback=None,
                  package_load_callback=None, buf=None, suppress_passive=False,
-                 print_stats=False, package_caching=True):
+                 print_stats=False, package_caching=None):
         """Perform a package resolve, and store the result.
 
         Args:
@@ -188,9 +188,10 @@ def __init__(self, package_requests, verbosity=0, timestamp=None,
             suppress_passive (bool): If True, don't print debugging info that
                 has had no effect on the solve. This argument only has an
                 effect if `verbosity` > 2.
-            print_stats (bool): If true, print advanced solver stats at the end.
-            package_caching (bool): If True, apply package caching settings as
-                per the config.
+            print_stats (bool): If True, print advanced solver stats at the end.
+            package_caching (bool|None): If True, apply package caching settings
+                as per the config. If None, enable as determined by config
+                setting 'package_cache_during_build'.
         """
         self.load_path = None
 
@@ -226,6 +227,13 @@ def __init__(self, package_requests, verbosity=0, timestamp=None,
 
         # settings that affect context execution
         self.append_sys_path = True
+
+        if package_caching is None:
+            if building:
+                package_caching = config.package_cache_during_build
+            else:
+                package_caching = True
+
         self.package_caching = package_caching
 
         # patch settings

src/rez/rezconfig.py

@@ -258,6 +258,9 @@
 # To disable, set to zero.
 package_cache_max_variant_days = 30
 
+# Enable package caching during a package build.
+package_cache_during_build = False
+
 # Allow caching of local packages. You would only want to set this True for
 # testing purposes.
 package_cache_local = False