Add lint for trait default impl removed

src/lints/trait_default_impl_removed.ron

@@ -0,0 +1,62 @@
+SemverQuery(
+    id: "trait_default_impl_removed",
+    human_readable_name: "pub trait default method impl removed",
+    description: "A non-sealed public trait default method impl was removed",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://doc.rust-lang.org/book/ch10-02-traits.html#default-implementations"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+                        sealed @filter(op: "!=", value: ["$true"])
+                        name @output
+
+                        importable_path {
+                            path @output @tag
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        method {
+                            method_name: name @output @tag
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            has_body @filter(op: "=", value: ["$true"])
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        sealed @filter(op: "!=", value: ["$true"])
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        method {
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            name @filter(op: "=", value: ["%method_name"])
+                            has_body @filter(op: "!=", value: ["$true"])
+                            span_: span @optional {
+                                filename @output
+                                begin_line @output
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "true": true,
+        "public": "public",
+    },
+    error_message: "A trait's method default impl was removed, breaking users relying on the default impl",
+    per_result_error_template: Some("trait method <{{join \"::\" path}}>::{{method_name}} in file {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -835,6 +835,7 @@ add_lints!(
     struct_with_pub_fields_changed_type,
     trait_associated_const_now_doc_hidden,
     trait_associated_type_now_doc_hidden,
+    trait_default_impl_removed,
     trait_method_missing,
     trait_method_now_doc_hidden,
     trait_method_unsafe_added,

test_crates/trait_default_impl_removed/new/Cargo.toml

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

test_crates/trait_default_impl_removed/new/src/lib.rs

@@ -0,0 +1,18 @@
+// Default trait method impl is removed, should be reported
+pub trait TraitA {
+    fn method_default_impl_removed(&self);
+}
+
+// Default trait method becomes removed completely, should not be reported as it becomes
+// missing instead
+pub trait TraitB {}
+
+//Default trait method impl is removed, but its private, shouldnt be reported
+trait TraitC {
+    fn method_default_impl_removed(&self);
+}
+
+// Non-object safe trait has its default impl removed, should be reported
+pub trait TraitD {
+    fn method_becomes_non_obj_safe(&self) -> Self;
+}

test_crates/trait_default_impl_removed/old/Cargo.toml

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

test_crates/trait_default_impl_removed/old/src/lib.rs

@@ -0,0 +1,20 @@
+// Default trait method impl is removed, should be reported
+pub trait TraitA {
+    fn method_default_impl_removed(&self) {}
+}
+
+// Default trait method becomes removed completely, should not be reported as it becomes
+// missing instead
+pub trait TraitB {
+    fn method_becomes_removed(&self) {}
+}
+
+//Default trait method impl is removed, but its private, shouldnt be reported
+trait TraitC {
+    fn method_default_impl_removed(&self) {}
+}
+
+// Non-object safe trait has its default impl removed, should be reported
+pub trait TraitD {
+    fn method_becomes_non_obj_safe(&self) {}
+}

test_outputs/trait_default_impl_removed.output.ron

@@ -0,0 +1,39 @@
+{
+    "./test_crates/trait_default_impl_removed/": [
+        {
+            "method_name": String("method_default_impl_removed"),
+            "name": String("TraitA"),
+            "path": List([
+                String("trait_default_impl_removed"),
+                String("TraitA"),
+            ]),
+            "span_begin_line": Uint64(3),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+        {
+            "method_name": String("method_becomes_non_obj_safe"),
+            "name": String("TraitD"),
+            "path": List([
+                String("trait_default_impl_removed"),
+                String("TraitD"),
+            ]),
+            "span_begin_line": Uint64(17),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
+    "./test_crates/trait_no_longer_object_safe/": [
+        {
+            "method_name": String("by_ref"),
+            "name": String("RefTrait"),
+            "path": List([
+                String("trait_no_longer_object_safe"),
+                String("RefTrait"),
+            ]),
+            "span_begin_line": Uint64(3),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
+}

test_outputs/trait_method_missing.output.ron

@@ -1,4 +1,17 @@
 {
+     "./test_crates/trait_default_impl_removed/": [
+        {
+            "method_name": String("method_becomes_removed"),
+            "name": String("TraitB"),
+            "path": List([
+                String("trait_default_impl_removed"),
+                String("TraitB"),
+            ]),
+            "span_begin_line": Uint64(9),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
     "./test_crates/trait_method_missing/": [
         {
             "method_name": String("fooA"),

test_outputs/trait_no_longer_object_safe.output.ron

@@ -21,6 +21,18 @@
             "visibility_limit": String("public"),
         },
     ],
+    "./test_crates/trait_default_impl_removed/": [
+        {
+            "name": String("TraitD"),
+            "path": List([
+                String("trait_default_impl_removed"),
+                String("TraitD"),
+            ]),
+            "span_begin_line": Uint64(16),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
     "./test_crates/trait_no_longer_object_safe/": [
         {
             "name": String("RefTrait"),