Make constraint_setting / constraint_value non_configurable.

The concept of allowing what is fundamentally a constant to vary by target we are building for is too much to reason about, let along get the code correct.

PiperOrigin-RevId: 483748098
Change-Id: I966b7d21ad8d38de9867c870a0669e2123063809

src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java

@@ -43,7 +43,9 @@ public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env)
         constraint list (such as for a <code>config_setting</code>) that requires a particular value
         for that setting.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr(DEFAULT_CONSTRAINT_VALUE_ATTR, BuildType.NODEP_LABEL))
+        .add(
+            attr(DEFAULT_CONSTRAINT_VALUE_ATTR, BuildType.NODEP_LABEL)
+                .nonconfigurable("constants must be consistent across configurations"))
         .build();
   }
 

src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java

@@ -42,7 +42,8 @@ public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env)
                 .mandatory()
                 .allowedRuleClasses(ConstraintSettingRule.RULE_NAME)
                 .allowedFileTypes(FileTypeSet.NO_FILE)
-                .mandatoryProviders(ConstraintSettingInfo.PROVIDER.id()))
+                .mandatoryProviders(ConstraintSettingInfo.PROVIDER.id())
+                .nonconfigurable("constants must be consistent across configurations"))
         .build();
   }