final minimal working example

e1/BUILD → BUILD

@@ -1,7 +1,11 @@
-load("//e1:build_settings.bzl", "flavor")
+load("//:build_settings.bzl", "flavor")
 flavor(
     name = "favorite_flavor",
     build_setting_default = False,
     visibility = ["//visibility:public"],
 )
 
+load("//:rules.bzl", "drink_rule")
+drink_rule(
+    name = "my_drink",
+)

README.md

@@ -1,24 +1,43 @@
 ## Example of [build configurations](https://docs.bazel.build/versions/0.28.0/skylark/config.html)
 
-This is to show off Bazel's ([recently added](https://docs.bazel.build/versions/0.28.0/skylark/config.html)) ability
+This is to show a bug in Bazel's ([recently added](https://docs.bazel.build/versions/0.28.0/skylark/config.html)) ability
 to employ user-defined build flags.
 
+### The minimal working setup
+
 If you do:
 
 ```bash
-bazel clean && bazel build //e1:my_drink
+bazel clean && bazel build //:my_drink
 ```
 it will print:
 ```
-DEBUG: .../e1/rules.bzl:7:9: Get the default (False)
+DEBUG: .../rules.bzl:7:9: Get the default (False)
 ```
 
 In contrast, if you do
 ```bash
-bazel clean && bazel build //e1:my_drink --//e1:favorite_flavor=True
+bazel clean && bazel build //:my_drink --//:favorite_flavor=True
 ```
 it will print:
 
 ```
-DEBUG: .../e1/rules.bzl:5:9: Get the opposite of default
+DEBUG: .../rules.bzl:5:9: Get the opposite of default (True)
+```
+
+### The bug (branch: bug)
+
+Same code, except using workspace prefix for referencing the build-sertting target. Both commands listed above yield the same result:
+```
+DEBUG: .../rules.bzl:7:9: Get the default (False)
+```
+That is, the flag set in the command-line has no effect. 
+It might make sense to modify the command to use the 
+workspace prefix too:
+```bash
+bazel clean && bazel build //:my_drink --@bsws//:favorite_flavor=True
+```
+Unfortunately (and surpriingly) this yields:
+```
+ERROR: Unrecognized option: --@bsws//:favorite_flavor=True
 ```

WORKSPACE

@@ -1 +1 @@
-#workspace(name = "bsws")
+workspace(name = "bsws")

rules.bzl

@@ -0,0 +1,16 @@
+load("//:build_settings.bzl", "FlavorProvider")
+def _rule_impl(ctx):
+    type = ctx.attr.flavor[FlavorProvider].type
+    if type:
+        print("Get the opposite of default (True)")
+    else:
+        print("Get the default (False)")
+
+drink_rule = rule(
+    implementation = _rule_impl,
+    attrs = {
+        "flavor": attr.label(
+            default = "//:favorite_flavor",
+        )
+    }
+)