Bug 1867459 - Avoiding silently dismissing uses of CPU_ARCH. r=firefox-build-system-reviewers,sergesanspaille

In many cases, using CONFIG["CPU_ARCH"] will silently do the unexpected
thing now that it doesn't exist anymore. In case there are in-flight
patches using it, it's better to avoid those causing subtle problems
after a rebase by making most uses of the variable throw an exception.

Differential Revision: https://phabricator.services.mozilla.com/D195158

build/moz.configure/init.configure

@@ -825,6 +825,7 @@ set_config("OS_TARGET", target_variables.OS_TARGET)
 add_old_configure_assignment("OS_TARGET", target_variables.OS_TARGET)
 set_config("OS_ARCH", target_variables.OS_ARCH)
 add_old_configure_assignment("OS_ARCH", target_variables.OS_ARCH)
+obsolete_config("CPU_ARCH", replacement="TARGET_CPU")
 set_config("INTEL_ARCHITECTURE", target_variables.INTEL_ARCHITECTURE)
 set_config("TARGET_CPU", target.cpu)
 add_old_configure_assignment("TARGET_CPU", target.cpu)

build/moz.configure/util.configure

@@ -515,6 +515,12 @@ def project_flag(env=None, set_as_define=False, **kwargs):
         set_define(env, option_implementation)
 
 
+@template
+@imports(_from="mozbuild.configure.constants", _import="RaiseErrorOnUse")
+def obsolete_config(name, *, replacement):
+    set_config(name, RaiseErrorOnUse(f"{name} is obsolete. Use {replacement} instead."))
+
+
 # Hacks related to old-configure
 # ==============================
 

python/mozbuild/mozbuild/configure/constants.py

@@ -7,6 +7,20 @@ from collections import OrderedDict
 from mozbuild.util import EnumString
 
 
+class RaiseErrorOnUse(str):
+    def __init__(self, msg):
+        self.msg = msg
+
+    def __eq__(self, other):
+        raise RuntimeError(self.msg)
+
+    def __ne__(self, other):
+        self.__eq__(other)
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}({self.msg!r})"
+
+
 class CompilerType(EnumString):
     POSSIBLE_VALUES = (
         "clang",