Implement trait_newly_sealed new lint

src/lints/trait_newly_sealed.ron

@@ -0,0 +1,52 @@
+SemverQuery(
+    id: "trait_newly_sealed",
+    human_readable_name: "pub trait became sealed",
+    description: "A public trait became sealed, so users of this trait can not implement it anymore",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://rust-lang.github.io/api-guidelines/future-proofing.html#sealed-traits-protect-against-downstream-implementations-c-sealed"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+                        sealed @filter(op: "!=", value: ["$true"])
+
+                        importable_path {
+                            path @output @tag
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        sealed @filter(op: "=", value: ["$true"])
+                        name @output
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "true": true,
+    },
+    error_message: "A publicly-visible trait became sealed, so downstream crates are no longer able to implement it",
+    per_result_error_template: Some("trait {{join \"::\" path}} in file {{span_filename}}:{{span_begin_line}}"),
+
+)

src/query.rs

@@ -841,6 +841,7 @@ add_lints!(
     trait_method_unsafe_removed,
     trait_missing,
     trait_must_use_added,
+    trait_newly_sealed,
     trait_no_longer_object_safe,
     trait_now_doc_hidden,
     trait_removed_associated_constant,

test_crates/trait_newly_sealed/new/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "trait_newly_sealed"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/trait_newly_sealed/new/src/lib.rs

@@ -0,0 +1,24 @@
+mod private {
+    pub trait Sealed {}
+    pub struct Token;
+}
+
+// Public trait becomes sealed, should be reported
+pub trait TraitBecomesSealed: private::Sealed {}
+
+// Trait that was not publicly-visible becomes sealed, shouldnt get reported as its still private
+trait TraitRemainsPrivateButSealed: private::Sealed {}
+
+// Method on public trait becomes sealed, should be reported
+pub trait TraitMethodBecomesSealed {
+    fn method(&self, _: private::Token);
+}
+
+// Trait that was not publicly-visible becomes public and sealed, shouldnt be
+// reported
+pub trait TraitBecomesPublicAndSealed: private::Sealed {}
+
+// Trait becomes private and sealed. The fact that it's private dominates,
+// and should be the only violation that's reported:
+// Thus being newly sealed is not the main problem
+trait TraitBecomesPrivateAndSealed: private::Sealed {}

test_crates/trait_newly_sealed/old/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "trait_newly_sealed"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/trait_newly_sealed/old/src/lib.rs

@@ -0,0 +1,18 @@
+// Public trait becomes sealed, should be reported
+pub trait TraitBecomesSealed {}
+
+// Trait that was not publicly-visible becomes sealed, shouldnt get reported as its still private
+trait TraitRemainsPrivateButSealed {}
+
+// Method on public trait becomes sealed, should be reported
+pub trait TraitMethodBecomesSealed {
+    fn method(&self);
+}
+// Trait that was not publicly-visible becomes public and sealed, shouldnt be
+// reported
+trait TraitBecomesPublicAndSealed {}
+
+// Trait becomes private and sealed. The fact that it's private dominates,
+// and should be the only violation that's reported:
+// Thus being newly sealed is not the main problem
+pub trait TraitBecomesPrivateAndSealed {}

test_outputs/trait_missing.output.ron

@@ -181,4 +181,16 @@
             "visibility_limit": String("public"),
         },
     ],
+    "./test_crates/trait_newly_sealed/": [
+        {
+            "name": String("TraitBecomesPrivateAndSealed"),
+            "path": List([
+                String("trait_newly_sealed"),
+                String("TraitBecomesPrivateAndSealed"),
+            ]),
+            "span_begin_line": Uint64(18),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
 }

test_outputs/trait_newly_sealed.output.ron

@@ -0,0 +1,25 @@
+{
+ "./test_crates/trait_newly_sealed/": [
+        {
+            "name": String("TraitBecomesSealed"),
+            "path": List([
+                String("trait_newly_sealed"),
+                String("TraitBecomesSealed"),
+            ]),
+            "span_begin_line": Uint64(7),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+        {
+            "name": String("TraitMethodBecomesSealed"),
+            "path": List([
+                String("trait_newly_sealed"),
+                String("TraitMethodBecomesSealed"),
+            ]),
+            "span_begin_line": Uint64(13),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
+}
+