Resolve failure on bazel 4 due to usage of ctx.resolve_command

.bazelci/config.yaml

@@ -191,8 +191,14 @@ tasks:
     platform: ubuntu1804
     build_targets:
       - "//..."
+    # experimental_enable_aggregating_middleman=False is required in bazel 4 otherwise ctx.resolve_command fails.
+    # This was resolved in https://github.com/bazelbuild/bazel/commit/fb1c369530bd26f9a13560c5979929a999e585e2
+    build_flags:
+      - "--experimental_enable_aggregating_middleman=False"
     test_targets:
       - "//..."
+    test_flags:
+      - "--experimental_enable_aggregating_middleman=False"
   min_supported_version_examples:
     name: "Minimum Supported Version Examples"
     bazel: "4.0.0"
@@ -201,7 +207,12 @@ tasks:
     min_supported_targets: &min_supported_targets
       - "//..."
     build_targets: *min_supported_targets
+    # See comment above regarding --experimental_enable_aggregating_middleman=False
+    build_flags:
+      - "--experimental_enable_aggregating_middleman=False"
     test_targets: *min_supported_targets
+    test_flags:
+      - "--experimental_enable_aggregating_middleman=False"
 
 buildifier:
   version: "4.2.5" 

README.md

@@ -13,7 +13,11 @@ Documentation for all rules and providers are available at: https://bazelbuild.g
 
 ## Bazel versions compatibility
 
-Works with Bazel after 4.0.0 without any flags.
+Works with Bazel after 4.0.0. 
+
+The following flags are required in Bazel 4.x but not Bazel 5.x or newer:
+
+- `--experimental_enable_aggregating_middleman=False`
 
 Note that the rules may be compatible with older versions of Bazel but support may break
 in future changes as these older versions are not tested.