Don't allow signal definition to reference attributes with lower stability than the signal itself

.chloggen/group-stability-check.yaml

@@ -0,0 +1,6 @@
+change_type: enhancement
+component: docs
+note: >
+  Don't allow signal definition to reference attributes with lower stability
+  than the signal itself (unless they are opt-in).
+issues: [3752]

docs/general/semantic-convention-groups.md

@@ -48,6 +48,15 @@ to preserve code generation and documentation for legacy instrumentations.
 
 When group is renamed or no longer recommended, it SHOULD be deprecated.
 
+A group SHOULD NOT reference attributes with a lower maturity level than the
+group itself, unless the requirement level of that attribute is `opt_in`.
+The requirement level of such an attribute reference MAY be changed once the
+attribute reaches the group's stability level, in cases allowed by
+[Versioning and Stability][Stability].
+For example, a `stable` event may reference a `development` attribute only at
+the `opt_in` requirement level; that requirement level may change once the
+attribute becomes stable as well.
+
 See [Versioning and Stability][Stability] for the details on stability guarantees
 provided for semantic convention groups of different types.
 
@@ -71,11 +80,6 @@ Stability guarantees on a group level **do not** apply to unstable attribute ref
 
 - MAY add or remove references to unstable attributes with `opt_in`
   requirement level.
-- SHOULD NOT have references to unstable attributes with requirement level
-  other than `opt_in`.
-  The requirement level of an unstable attribute reference
-  MAY be changed when this attribute becomes stable in cases allowed by the
-  [Versioning and Stability][Stability].
 - MUST NOT remove references to stable attributes.
 
 Stable instrumentations MUST NOT report telemetry following the unstable part

policies/group_stability.rego

@@ -1,11 +1,22 @@
 package after_resolution
 import rego.v1
-# checks that stable group does not have experimental attributes with requirement levels other than opt_in
+
+# Maturity ranking of stability levels. Higher number == more mature/stable.
+stability_rank := {
+    "development": 1,
+    "experimental": 1,
+    "alpha": 2,
+    "beta": 3,
+    "release_candidate": 4,
+    "stable": 5,
+}
+
+# checks that a group's stability is not higher than the stability of any of its
+# attributes, unless that attribute is opt_in
 deny contains group_stability_violation(description, group.id, name) if {
     group := input.groups[_]
     # ignore attribute_groups
     group.type != "attribute_group"
-    group.stability == "stable"
 
     exceptions = {
         # TODO: https://github.com/open-telemetry/semantic-conventions/issues/1514
@@ -14,17 +25,24 @@ deny contains group_stability_violation(description, group.id, name) if {
         "entity.service",
         # TODO: https://github.com/open-telemetry/semantic-conventions/issues/1616
         "metric.dotnet.process.cpu.time",
+        # TODO: https://github.com/open-telemetry/semantic-conventions/issues/3753
+        "span.db.oracledb.client",
     }
     not exceptions[group.id]
 
+    group_rank := stability_rank[group.stability]
+
     attr := group.attributes[_]
+    not attr.requirement_level == "opt_in"
+
+    attr_rank := stability_rank[attr.stability]
 
-    attr.stability != "stable"
-    attr.requirement_level != "opt_in"
+    # group claims a higher maturity than the attribute it references
+    group_rank > attr_rank
 
     name := attr.name
 
-    description := sprintf("Stable group '%s' references experimental attribute with requirement level '%s', only 'opt_in' level is allowed", [group.id, name])
+    description := sprintf("Group '%s' has stability '%s' which is higher than the stability '%s' of attribute '%s'; lower-stability attributes are only allowed at 'opt_in' requirement level", [group.id, group.stability, attr.stability, name])
 }
 
 group_stability_violation(description, group, attr) = violation if {

policies_test/group_stability_test.rego

@@ -1,34 +1,69 @@
 package after_resolution
 import future.keywords
 
-test_fails_on_experimental_not_opt_in_attribute_in_stable_group if {
-    experimental_stabilities := ["experimental", "development", "alpha", "beta", "release_candidate"]
-    every stability in experimental_stabilities {
-        count(deny) == 1 with input as {"groups": [{ "id": "span.foo",
-                                            "type": "span",
-                                            "stability": "stable",
-                                            "brief": "brief.",
-                                            "attributes": [{
-                                                "name": "test.experimental",
-                                                "stability": stability,
-                                                "requirement_level": "required",
-                                                "brief": "brief.",
-                                            }]}]}
+gs_group_types := ["span", "metric", "event", "entity"]
+
+gs_lower_stabilities := ["experimental", "development", "alpha", "beta", "release_candidate"]
+
+# Builds an input with a single group of the given type referencing a single attribute.
+gs_input(group_type, group_stability, attr_stability, requirement_level) := {"groups": [{
+    "id": sprintf("%s.foo", [group_type]),
+    "type": group_type,
+    "stability": group_stability,
+    "brief": "brief.",
+    "attributes": [{
+        "name": "test.attr",
+        "stability": attr_stability,
+        "requirement_level": requirement_level,
+        "brief": "brief.",
+    }],
+}]}
+
+# A group must not reference a lower-maturity attribute unless it's opt_in.
+test_fails_on_lower_maturity_not_opt_in_attribute if {
+    every group_type in gs_group_types {
+        every stability in gs_lower_stabilities {
+            count(deny) == 1 with input as gs_input(group_type, "stable", stability, "required")
+        }
+    }
+}
+
+test_passes_on_lower_maturity_opt_in_attribute if {
+    every group_type in gs_group_types {
+        every stability in gs_lower_stabilities {
+            count(deny) == 0 with input as gs_input(group_type, "stable", stability, "opt_in")
+        }
+    }
+}
+
+# Group stability higher than the attribute's (non-stable group) still fails.
+test_fails_when_group_stability_higher_than_attribute if {
+    every group_type in gs_group_types {
+        count(deny) == 1 with input as gs_input(group_type, "release_candidate", "development", "required")
     }
 }
 
-test_passes_on_experimental_opt_in_attribute_in_stable_group if {
-    experimental_stabilities := ["experimental", "development", "alpha", "beta", "release_candidate"]
-    every stability in experimental_stabilities {
-        count(deny) == 0 with input as {"groups": [{ "id": "span.foo",
-                                        "type": "span",
-                                        "stability": "stable",
-                                        "brief": "brief.",
-                                        "attributes": [{
-                                            "name": "test.experimental",
-                                            "stability": stability,
-                                            "requirement_level": "opt_in",
-                                            "brief": "brief.",
-                                        }]}]}
+# A lower-stability group referencing a higher-stability attribute is fine.
+test_passes_when_group_stability_lower_than_attribute if {
+    every group_type in gs_group_types {
+        count(deny) == 0 with input as gs_input(group_type, "development", "stable", "required")
     }
 }
+
+test_passes_when_group_and_attribute_have_equal_stability if {
+    every group_type in gs_group_types {
+        count(deny) == 0 with input as gs_input(group_type, "release_candidate", "release_candidate", "required")
+    }
+}
+
+# A lower-stability attribute is allowed at opt_in in a more stable group.
+test_passes_on_lower_stability_opt_in_attribute if {
+    every group_type in gs_group_types {
+        count(deny) == 0 with input as gs_input(group_type, "release_candidate", "development", "opt_in")
+    }
+}
+
+# attribute_group is exempt from the check regardless of stability.
+test_passes_on_attribute_group if {
+    count(deny) == 0 with input as gs_input("attribute_group", "stable", "development", "required")
+}