Add new lint: trait_method_unsafe_added (#605)

src/lints/trait_method_unsafe_added.ron

@@ -0,0 +1,59 @@
+SemverQuery(
+    id: "trait_method_unsafe_added",
+    human_readable_name: "pub trait method became unsafe",
+    description: "A method in a public trait became unsafe",
+    required_update: Major,
+    reference_link: Some("https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html#calling-an-unsafe-function-or-method"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+
+                        importable_path {
+                            path @output @tag
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        method {
+                            unsafe @filter(op: "!=", value: ["$true"])
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            method_name: name @output @tag
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        method {
+                            unsafe @filter(op: "=", value: ["$true"])
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            name @filter(op: "=", value: ["%method_name"])
+
+                            span_: span @optional {
+                                filename @output
+                                begin_line @output
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "true": true,
+        "public": "public",
+    },
+    error_message: "A publicly-visible trait method became `unsafe`, so implementing it now requires an `unsafe` qualifier.",
+    per_result_error_template: Some("trait method <{{join \"::\" path}}>::{{method_name}} in file {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -521,4 +521,5 @@ add_lints!(
     module_missing,
     trait_removed_associated_constant,
     function_changed_abi,
+    trait_method_unsafe_added,
 );

test_crates/trait_method_unsafe_added/new/Cargo.toml

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

test_crates/trait_method_unsafe_added/new/src/lib.rs

@@ -0,0 +1,30 @@
+// Method of public trait becomes unsafe, should get reported.
+pub trait PubTrait {
+    unsafe fn becomes_unsafe();
+    fn stays_safe();
+    unsafe fn stays_unsafe();
+}
+
+// Method of trait that was not publicly-visible becomes unsafe, shouldn't get
+// reported.
+pub trait TraitBecomesPublic {
+    unsafe fn becomes_unsafe();
+}
+
+// Method of trait that is publicly-visible becomes unsafe while trait becomes
+// private. The trait becoming private should be the only violation that's
+// reported.
+trait TraitBecomesPrivate {
+    unsafe fn becomes_unsafe();
+}
+
+// Method of trait becomes unsafe while trait also becomes unsafe. Method should
+// get reported along with trait.
+pub unsafe trait TraitBecomesUnsafe {
+    unsafe fn becomes_unsafe();
+}
+
+// Private trait's method becomes unsafe, shouldn't get reported.
+trait PrivateTrait {
+    unsafe fn becomes_unsafe();
+}

test_crates/trait_method_unsafe_added/old/Cargo.toml

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

test_crates/trait_method_unsafe_added/old/src/lib.rs

@@ -0,0 +1,30 @@
+// Method of public trait becomes unsafe, should get reported.
+pub trait PubTrait {
+    fn becomes_unsafe();
+    fn stays_safe();
+    unsafe fn stays_unsafe();
+}
+
+// Method of trait that was not publicly-visible becomes unsafe, shouldn't get
+// reported.
+trait TraitBecomesPublic {
+    fn becomes_unsafe();
+}
+
+// Method of trait that is publicly-visible becomes unsafe while trait becomes
+// private. The trait becoming private should be the only violation that's
+// reported.
+pub trait TraitBecomesPrivate {
+    fn becomes_unsafe();
+}
+
+// Method of trait becomes unsafe while trait also becomes unsafe. Method should
+// get reported along with trait.
+pub trait TraitBecomesUnsafe {
+    fn becomes_unsafe();
+}
+
+// Private trait's method becomes unsafe, shouldn't get reported.
+trait PrivateTrait {
+    fn becomes_unsafe();
+}

test_outputs/trait_method_unsafe_added.output.ron

@@ -0,0 +1,24 @@
+{
+    "./test_crates/trait_method_unsafe_added/": [
+        {
+            "method_name": String("becomes_unsafe"),
+            "path": List([
+                String("trait_method_unsafe_added"),
+                String("PubTrait"),
+            ]),
+            "span_begin_line": Uint64(3),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+        {
+            "method_name": String("becomes_unsafe"),
+            "path": List([
+                String("trait_method_unsafe_added"),
+                String("TraitBecomesUnsafe"),
+            ]),
+            "span_begin_line": Uint64(24),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        }
+    ],
+}

test_outputs/trait_missing.output.ron

@@ -35,6 +35,18 @@
             "visibility_limit": String("public"),
         },
     ],
+    "./test_crates/trait_method_unsafe_added/": [
+        {
+            "name": String("TraitBecomesPrivate"),
+            "path": List([
+                String("trait_method_unsafe_added"),
+                String("TraitBecomesPrivate"),
+            ]),
+            "span_begin_line": Uint64(17),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
     "./test_crates/trait_missing/": [
         {
             "name": String("RemovedTrait"),

test_outputs/trait_unsafe_added.output.ron

@@ -1,4 +1,16 @@
 {
+    "./test_crates/trait_method_unsafe_added/": [
+        {
+            "name": String("TraitBecomesUnsafe"),
+            "path": List([
+                String("trait_method_unsafe_added"),
+                String("TraitBecomesUnsafe"),
+            ]),
+            "span_begin_line": Uint64(23),
+            "span_filename": String("src/lib.rs"),
+            "visibility_limit": String("public"),
+        },
+    ],
     "./test_crates/trait_missing/": [
         {
             "name": String("TraitBecomesUnsafe"),